Monam Agarwal [Sun, 23 Mar 2014 18:47:18 +0000 (00:17 +0530)]
cgroup: Use RCU_INIT_POINTER(x, NULL) in cgroup.c
This patch replaces rcu_assign_pointer(x, NULL) with
RCU_INIT_POINTER(x, NULL)
The rcu_assign_pointer() ensures that the initialization of a
structure is carried out before storing a pointer to that structure.
And in the case of the NULL pointer, there is no structure to
initialize. So, rcu_assign_pointer(p, NULL) can be safely converted
to RCU_INIT_POINTER(p, NULL)
Tejun Heo [Thu, 20 Mar 2014 15:10:15 +0000 (11:10 -0400)]
cgroup: break kernfs active_ref protection in cgroup directory operations
cgroup_tree_mutex should nest above the kernfs active_ref protection;
however, cgroup_create() and cgroup_rename() were grabbing
cgroup_tree_mutex while under kernfs active_ref protection. This has
actualy possibility to lead to deadlocks in case these operations race
against cgroup_rmdir() which invokes kernfs_remove() on directory
kernfs_node while holding cgroup_tree_mutex.
Neither cgroup_create() or cgroup_rename() requires active_ref
protection. The former already has enough synchronization through
cgroup_lock_live_group() and the latter doesn't care, so this can be
fixed by updating both functions to break all active_ref protections
before grabbing cgroup_tree_mutex.
While this patch fixes the immediate issue, it probably needs further
work in the long term - kernfs directories should enable lockdep
annotations and maybe the better way to handle this is marking
directory nodes as not needing active_ref protection rather than
breaking it in each operation.
Tejun Heo [Wed, 19 Mar 2014 21:43:21 +0000 (17:43 -0400)]
cgroup: fix cgroup_taskset walking order
cgroup_taskset is used to track and iterate target tasks while
migrating a task or process and should guarantee that the first task
iterated is the task group leader if a process is being migrated.
b3dc094e9390 ("cgroup: use css_set->mg_tasks to track target tasks
during migration") replaced flex array cgroup_taskset->tc_array with
css_set->mg_tasks list to remove process size limit and dynamic
allocation during migration; unfortunately, it incorrectly used list
operations which don't preserve order breaking the guarantee that
cgroup_taskset_first() returns the leader for a process target.
Fix it by using order preserving list operations. Note that as
multiple src_csets may map to a single dst_cset, the iteration order
may change across cgroup_task_migrate(); however, the leader is still
guaranteed to be the first entry.
The switch to list_splice_tail_init() at the end of cgroup_migrate()
isn't strictly necessary. Let's still do it for consistency.
Tejun Heo [Wed, 19 Mar 2014 14:23:55 +0000 (10:23 -0400)]
cgroup: make cgrp_dfl_root mountable
cgrp_dfl_root will be used as the default unified hierarchy. This
patch makes cgrp_dfl_root mountable by making the following changes.
* cgroup_init_early() now initializes cgrp_dfl_root w/
CGRP_ROOT_SANE_BEHAVIOR. The default hierarchy is always sane.
* parse_cgroupfs_options() and cgroup_mount() are updated such that
cgrp_dfl_root is mounted if sane_behavior is specified w/o any
subsystems.
* rebind_subsystems() now populates the root directory of
cgrp_dfl_root. Note that the function still guarantees success of
rebinding subsystems to cgrp_dfl_root. If populating fails while
rebinding to cgrp_dfl_root, it whines but ignores the error.
* For backward compatibility, the default hierarchy shows up in
/proc/$PID/cgroup only after it's explicitly mounted so that
userland which doesn't make use of it doesn't see any change.
* "current_css_set_cg_links" file of debug cgroup now treats the
default hierarchy the same as other hierarchies. This is visible to
userland. Given that it's for debug controller, this should be
fine.
* While at it, implement cgroup_on_dfl() which tests whether a give
cgroup is on the default hierarchy or not.
The above changes make cgrp_dfl_root mostly equivalent to other
controllers but the actual unified hierarchy behaviors are not
implemented yet. Let's plug child cgroup creation in cgrp_dfl_root
from create_cgroup() for now.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Tejun Heo [Wed, 19 Mar 2014 14:23:54 +0000 (10:23 -0400)]
cgroup: drop const from @buffer of cftype->write_string()
cftype->write_string() just passes on the writeable buffer from kernfs
and there's no reason to add const restriction on the buffer. The
only thing const achieves is unnecessarily complicating parsing of the
buffer. Drop const from @buffer.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Paul Mackerras <paulus@samba.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net> Cc: Daniel Borkmann <dborkman@redhat.com> Cc: Michal Hocko <mhocko@suse.cz> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Balbir Singh <bsingharora@gmail.com> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Tejun Heo [Wed, 19 Mar 2014 14:23:54 +0000 (10:23 -0400)]
cgroup: rename cgroup_dummy_root and related names
The dummy root will be repurposed to serve as the default unified
hierarchy. Let's rename things in preparation.
* s/cgroup_dummy_root/cgrp_dfl_root/
* s/cgroupfs_root/cgroup_root/ as we don't do fs part directly anymore
* s/cgroup_root->top_cgroup/cgroup_root->cgrp/ for brevity
This is pure rename.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Tejun Heo [Wed, 19 Mar 2014 14:23:54 +0000 (10:23 -0400)]
cgroup: move ->subsys_mask from cgroupfs_root to cgroup
cgroupfs_root->subsys_mask represents the controllers attached to the
hierarchy. This patch moves the field to cgroup. Subsystem
initialization and rebinding updates the top cgroup's subsys_mask.
For !root cgroups, the subsys_mask bits are set from create_css() and
cleared from kill_css(), which effectively means that all cgroups will
have the same subsys_mask as the top cgroup.
While this doesn't make any difference now, this will help
implementation of the default unified hierarchy where !root cgroups
may have subsets of the top_cgroup's subsys_mask.
While at it, __kill_css() is split out of kill_css(). The former
doesn't care about the subsys_mask while the latter becomes noop if
the controller is already killed and clears the matching bit if not
before proceeding to killing the css. This will be used later by the
default unified hierarchy implementation.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Tejun Heo [Wed, 19 Mar 2014 14:23:54 +0000 (10:23 -0400)]
cgroup: treat cgroup_dummy_root as an equivalent hierarchy during rebinding
Currently, while rebinding, cgroup_dummy_root serves as the anchor
point. In addition to the target root, rebind_subsystems() takes
@added_mask and @removed_mask. The subsystems specified in the former
are expected to be on the dummy root and then moved to the target
root. The ones in the latter are moved from non-dummy root to dummy.
Now that the dummy root is a fully functional one and we're planning
to use it for the default unified hierarchy, this level of distinction
between dummy and non-dummy roots is quite awkward.
This patch updates rebind_subsystems() to take the target root and one
subsystem mask and move the specified subsystmes to the target root
which may or may not be the dummy root. IOW, unbinding now becomes
moving the subsystems to the dummy root and binding to non-dummy root.
This makes the dummy root mostly equivalent to other hierarchies in
terms of the mechanism of moving subsystems around; however, we still
retain all the semantical restrictions so that this patch doesn't
introduce any visible behavior differences. Another noteworthy detail
is that rebind_subsystems() guarantees that moving a subsystem to the
dummy root never fails so that valid unmounting attempts always
succeed.
This unifies binding and unbinding of subsystems. The invocation
points of ->bind() were inconsistent between the two and now moved
after whole rebinding is complete. This doesn't break the current
users and generally makes more sense.
All rebind_subsystems() users are converted accordingly. Note that
cgroup_remount() now makes two calls to rebind_subsystems() to bind
and then unbind the requested subsystems.
This will allow repurposing of the dummy hierarchy as the default
unified hierarchy and shouldn't make any userland visible behavior
difference.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Tejun Heo [Wed, 19 Mar 2014 14:23:54 +0000 (10:23 -0400)]
cgroup: remove NULL checks from [pr_cont_]cgroup_{name|path}()
The dummy hierarchy is now a fully functional one and dummy_top has a
kernfs_node associated with it. Drop the NULL checks in
[pr_cont_]cont_{name|path}() which are no longer necessary.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Tejun Heo [Wed, 19 Mar 2014 14:23:53 +0000 (10:23 -0400)]
cgroup: use cgroup_setup_root() to initialize cgroup_dummy_root
cgroup_dummy_root is used to host controllers which aren't attached to
any other hierarchy. The root is minimally set up during kernfs
bootstrap and didn't go through full hierarchy initialization. We're
planning to use cgroup_dummy_root for the default unified hierarchy
and thus want it to be fully functional.
Replace the special initialization, which was collected into
cgroup_init() by the previous patch, with an invocation of
cgroup_setup_root(). This simplifies the init path and makes
cgroup_dummy_root a full hierarchy with its own kernfs_root and all.
As this puts the dummy hierarchy on the cgroup_roots list, rename
for_each_active_root() to for_each_root() and update its users to skip
the dummy root for now.
This patch doesn't cause any userland visible behavior changes at this
point.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Tejun Heo [Wed, 19 Mar 2014 14:23:53 +0000 (10:23 -0400)]
cgroup: reorganize cgroup bootstrapping
* Fields of init_css_set and css_set_count are now set using
initializer instead of programmatically from cgroup_init_early().
* init_cgroup_root() now also takes @opts and performs the optional
part of initialization too. The leftover part of
cgroup_root_from_opts() is collapsed into its only caller -
cgroup_mount().
* Initialization of cgroup_root_count and linking of init_css_set are
moved from cgroup_init_early() to to cgroup_init(). None of the
early_init users depends on init_css_set being linked.
* Subsystem initializations are moved after dummy hierarchy init and
init_css_set linking.
These changes reorganize the bootstrap logic so that the dummy
hierarchy can share the usual hierarchy init path and be made more
normal. These changes don't make noticeable behavior changes.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Tejun Heo [Wed, 19 Mar 2014 14:23:53 +0000 (10:23 -0400)]
cgroup: relocate setting of CGRP_DEAD
In cgroup_destroy_locked(), move setting of CGRP_DEAD above
invocations of kill_css(). This doesn't make any visible behavior
difference now but will be used to inhibit manipulating controller
enable states of a dying cgroup on the unified hierarchy.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
cgroup_subsys->fork() callback is special in that it's called outside
the usual cgroup locking and may race with on-going migration.
freezer_fork() currently doesn't consider such race condition;
however, it is still correct thanks to the fact that freeze_task() may
be called spuriously.
This is quite subtle. Let's explain what's going on and add test to
detect racing and losing to task migration and skip freeze_task() in
such cases for documentation.
This doesn't make any behavior difference meaningful to userland.
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Li Zefan <lizefan@huawei.com> Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Tejun Heo [Tue, 25 Feb 2014 15:04:03 +0000 (10:04 -0500)]
cgroup: update cgroup_transfer_tasks() to either succeed or fail
cgroup_transfer_tasks() can currently fail in the middle due to memory
allocation failure. When that happens, the function just aborts and
returns error code and there's no way to tell how many actually got
migrated at the point of failure and or to revert the partial
migration.
Update it to use cgroup_migrate{_add_src|prepare_dst|migrate|finish}()
so that the function either succeeds or fails as a whole as long as
->can_attach() doesn't fail.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Tejun Heo [Tue, 25 Feb 2014 15:04:03 +0000 (10:04 -0500)]
cgroup: drop task_lock() protection around task->cgroups
For optimization, task_lock() is additionally used to protect
task->cgroups. The optimization is pretty dubious as either
css_set_rwsem is grabbed anyway or PF_EXITING already protects
task->cgroups. It adds only overhead and confusion at this point.
Let's drop task_[un]lock() and update comments accordingly.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Tejun Heo [Tue, 25 Feb 2014 15:04:03 +0000 (10:04 -0500)]
cgroup: update how a newly forked task gets associated with css_set
When a new process is forked, cgroup_fork() associates it with the
css_set of its parent but doesn't link it into it. After the new
process is linked to tasklist, cgroup_post_fork() does the linking.
This is problematic for cgroup_transfer_tasks() as there's no way to
tell whether there are tasks which are pointing to a css_set but not
linked yet. It is impossible to implement an operation which transfer
all tasks of a cgroup to another and the current
cgroup_transfer_tasks() can easily be tricked into leaving a newly
forked process behind if it gets called between cgroup_fork() and
cgroup_post_fork().
Let's make association with a css_set and linking atomic by moving it
to cgroup_post_fork(). cgroup_fork() sets child->cgroups to
init_css_set as a placeholder and cgroup_post_fork() is updated to
perform both the association with the parent's cgroup and linking
there. This means that a newly created task will point to
init_css_set without holding a ref to it much like what it does on the
exit path. Empty cg_list is used to indicate that the task isn't
holding a ref to the associated css_set.
This fixes an actual bug with cgroup_transfer_tasks(); however, I'm
not marking it for -stable. The whole thing is broken in multiple
other ways which require invasive updates to fix and I don't think
it's worthwhile to bother with backporting this particular one.
Fortunately, the only user is cpuset and these bugs don't crash the
machine.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Tejun Heo [Tue, 25 Feb 2014 15:04:03 +0000 (10:04 -0500)]
cgroup: split process / task migration into four steps
Currently, process / task migration is a single operation which may
fail depending on memory pressure or the involved controllers'
->can_attach() callbacks. One problem with this approach is migration
of multiple targets. It's impossible to tell whether a given target
will be successfully migrated beforehand and cgroup core can't keep
track of enough states to roll back after intermediate failure.
This is already an issue with cgroup_transfer_tasks(). Also, we're
gonna need multiple target migration for unified hierarchy.
This patch splits migration into four stages -
cgroup_migrate_add_src(), cgroup_migrate_prepare_dst(),
cgroup_migrate() and cgroup_migrate_finish(), where
cgroup_migrate_prepare_dst() performs all the operations which may
fail due to allocation failure without actually migrating the target.
The four separate stages mean that, disregarding ->can_attach()
failures, the success or failure of multi target migration can be
determined before performing any actual migration. If preparations of
all targets succeed, the whole thing will succeed. If not, the whole
operation can fail without any side-effect.
Since the previous patch to use css_set->mg_tasks to keep track of
migration targets, the only thing which may need memory allocation
during migration is the target css_sets. cgroup_migrate_prepare()
pins all source and target css_sets and link them up. Note that this
can be performed without holding threadgroup_lock even if the target
is a process. As long as cgroup_mutex is held, no new css_set can be
put into play.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Tejun Heo [Tue, 25 Feb 2014 15:04:01 +0000 (10:04 -0500)]
cgroup: use css_set->mg_tasks to track target tasks during migration
Currently, while migrating tasks from one cgroup to another,
cgroup_attach_task() builds a flex array of all target tasks;
unfortunately, this has a couple issues.
* Flex array has size limit. On 64bit, struct task_and_cgroup is
24bytes making the flex element limit around 87k. It is a high
number but not impossible to hit. This means that the current
cgroup implementation can't migrate a process with more than 87k
threads.
* Process migration involves memory allocation whose size is dependent
on the number of threads the process has. This means that cgroup
core can't guarantee success or failure of multi-process migrations
as memory allocation failure can happen in the middle. This is in
part because cgroup can't grab threadgroup locks of multiple
processes at the same time, so when there are multiple processes to
migrate, it is imposible to tell how many tasks are to be migrated
beforehand.
Note that this already affects cgroup_transfer_tasks(). cgroup
currently cannot guarantee atomic success or failure of the
operation. It may fail in the middle and after such failure cgroup
doesn't have enough information to roll back properly. It just
aborts with some tasks migrated and others not.
To resolve the situation, this patch updates the migration path to use
task->cg_list to track target tasks. The previous patch already added
css_set->mg_tasks and updated iterations in non-migration paths to
include them during task migration. This patch updates migration path
to actually make use of it.
Instead of putting onto a flex_array, each target task is moved from
its css_set->tasks list to css_set->mg_tasks and the migration path
keeps trace of all the source css_sets and the associated cgroups.
Once all source css_sets are determined, the destination css_set for
each is determined, linked to the matching source css_set and put on a
separate list.
To iterate the target tasks, migration path just needs to iterat
through either the source or target css_sets, depending on whether
migration has been committed or not, and the tasks on their ->mg_tasks
lists. cgroup_taskset is updated to contain the list_heads for source
and target css_sets and the iteration cursor. cgroup_taskset_*() are
accordingly updated to walk through css_sets and their ->mg_tasks.
This resolves the above listed issues with moderate additional
complexity.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Tejun Heo [Tue, 25 Feb 2014 15:04:01 +0000 (10:04 -0500)]
cgroup: add css_set->mg_tasks
Currently, while migrating tasks from one cgroup to another,
cgroup_attach_task() builds a flex array of all target tasks;
unfortunately, this has a couple issues.
* Flex array has size limit. On 64bit, struct task_and_cgroup is
24bytes making the flex element limit around 87k. It is a high
number but not impossible to hit. This means that the current
cgroup implementation can't migrate a process with more than 87k
threads.
* Process migration involves memory allocation whose size is dependent
on the number of threads the process has. This means that cgroup
core can't guarantee success or failure of multi-process migrations
as memory allocation failure can happen in the middle. This is in
part because cgroup can't grab threadgroup locks of multiple
processes at the same time, so when there are multiple processes to
migrate, it is imposible to tell how many tasks are to be migrated
beforehand.
Note that this already affects cgroup_transfer_tasks(). cgroup
currently cannot guarantee atomic success or failure of the
operation. It may fail in the middle and after such failure cgroup
doesn't have enough information to roll back properly. It just
aborts with some tasks migrated and others not.
To resolve the situation, we're going to use task->cg_list during
migration too. Instead of building a separate array, target tasks
will be linked into a dedicated migration list_head on the owning
css_set. Tasks on the migration list are treated the same as tasks on
the usual tasks list; however, being on a separate list allows cgroup
migration code path to keep track of the target tasks by simply
keeping the list of css_sets with tasks being migrated, making
unpredictable dynamic allocation unnecessary.
In prepartion of such migration path update, this patch introduces
css_set->mg_tasks list and updates css_set task iterations so that
they walk both css_set->tasks and ->mg_tasks. Note that ->mg_tasks
isn't used yet.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Tejun Heo [Tue, 25 Feb 2014 14:56:49 +0000 (09:56 -0500)]
Merge branch 'cgroup/for-3.14-fixes' into cgroup/for-3.15
Pull in for-3.14-fixes to receive 532de3fc72ad ("cgroup: update
cgroup_enable_task_cg_lists() to grab siglock") which conflicts with afeb0f9fd425 ("cgroup: relocate cgroup_enable_task_cg_lists()") and
the following cg_lists updates. This is likely to cause further
conflicts down the line too, so let's merge it early.
As cgroup_enable_task_cg_lists() is relocated in for-3.15, this merge
causes conflict in the original position. It's resolved by applying
siglock changes to the updated version in the new location.
Tejun Heo [Thu, 13 Feb 2014 18:29:31 +0000 (13:29 -0500)]
cgroup: update cgroup_enable_task_cg_lists() to grab siglock
Currently, there's nothing preventing cgroup_enable_task_cg_lists()
from missing set PF_EXITING and race against cgroup_exit(). Depending
on the timing, cgroup_exit() may finish with the task still linked on
css_set leading to list corruption. Fix it by grabbing siglock in
cgroup_enable_task_cg_lists() so that PF_EXITING is guaranteed to be
visible.
This whole on-demand cg_list optimization is extremely fragile and has
ample possibility to lead to bugs which can cause things like
once-a-year oops during boot. I'm wondering whether the better
approach would be just adding "cgroup_disable=all" handling which
disables the whole cgroup rather than tempting fate with this
on-demand craziness.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com> Cc: stable@vger.kernel.org
Paul Gortmaker [Thu, 13 Feb 2014 15:59:18 +0000 (10:59 -0500)]
sparc: fix implicit include of slab.h in leon_pci_grpci2.c
To fix:
arch/sparc/kernel/leon_pci_grpci2.c: In function 'grpci2_of_probe':
arch/sparc/kernel/leon_pci_grpci2.c:720:2: error: implicit declaration of function 'kzalloc' [-Werror=implicit-function-declaration]
arch/sparc/kernel/leon_pci_grpci2.c:720:20: error: assignment makes pointer from integer without a cast [-Werror]
arch/sparc/kernel/leon_pci_grpci2.c:882:2: error: implicit declaration of function 'kfree' [-Werror=implicit-function-declaration]
cc1: all warnings being treated as errors
make[2]: *** [arch/sparc/kernel/leon_pci_grpci2.o] Error 1
According to Stephen, these types of failures are caused by commit 2bd59d48ebfb ("cgroup: convert to kernfs") which was being included
implicitly via cgroup.h's inclusion of xattr.h (which has now been
removed).
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com> Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: David S. Miller <davem@davemloft.net> Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Tejun Heo [Thu, 13 Feb 2014 11:58:41 +0000 (06:58 -0500)]
cpuset: don't use cgroup_taskset_cur_css()
cgroup_taskset_cur_css() will be removed during the planned
resturcturing of migration path. The only use of
cgroup_taskset_cur_css() is finding out the old cgroup_subsys_state of
the leader in cpuset_attach(). This usage can easily be removed by
remembering the old value from cpuset_can_attach().
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Tejun Heo [Thu, 13 Feb 2014 11:58:41 +0000 (06:58 -0500)]
cgroup: drop @skip_css from cgroup_taskset_for_each()
If !NULL, @skip_css makes cgroup_taskset_for_each() skip the matching
css. The intention of the interface is to make it easy to skip css's
(cgroup_subsys_states) which already match the migration target;
however, this is entirely unnecessary as migration taskset doesn't
include tasks which are already in the target cgroup. Drop @skip_css
from cgroup_taskset_for_each().
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Paul Mackerras <paulus@samba.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net> Cc: Daniel Borkmann <dborkman@redhat.com>
Tejun Heo [Thu, 13 Feb 2014 11:58:41 +0000 (06:58 -0500)]
cgroup: move css_set_rwsem locking outside of cgroup_task_migrate()
Instead of repeatedly locking and unlocking css_set_rwsem inside
cgroup_task_migrate(), update cgroup_attach_task() to grab it outside
of the loop and update cgroup_task_migrate() to use
put_css_set_locked().
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Tejun Heo [Thu, 13 Feb 2014 11:58:40 +0000 (06:58 -0500)]
cgroup: separate out put_css_set_locked() and remove put_css_set_taskexit()
put_css_set() is performed in two steps - it first tries to put
without grabbing css_set_rwsem if such put wouldn't make the count
zero. If that fails, it puts after write-locking css_set_rwsem. This
patch separates out the second phase into put_css_set_locked() which
should be called with css_set_rwsem locked.
Also, put_css_set_taskexit() is droped and put_css_set() is made to
take @taskexit. There are only a handful users of these functions.
No point in providing different variants.
put_css_locked() will be used by later changes. This patch doesn't
introduce any functional changes.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Tejun Heo [Thu, 13 Feb 2014 11:58:40 +0000 (06:58 -0500)]
cpuset: use css_task_iter_start/next/end() instead of css_scan_tasks()
Now that css_task_iter_start/next_end() supports blocking while
iterating, there's no reason to use css_scan_tasks() which is more
cumbersome to use and scheduled to be removed.
Convert all css_scan_tasks() usages in cpuset to
css_task_iter_start/next/end(). This simplifies the code by removing
heap allocation and callbacks.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Tejun Heo [Thu, 13 Feb 2014 11:58:40 +0000 (06:58 -0500)]
cgroup: make css_set_lock a rwsem and rename it to css_set_rwsem
Currently there are two ways to walk tasks of a cgroup -
css_task_iter_start/next/end() and css_scan_tasks(). The latter
builds on the former but allows blocking while iterating.
Unfortunately, the way css_scan_tasks() is implemented is rather
nasty, it uses a priority heap of pointers to extract some number of
tasks in task creation order and loops over them invoking the callback
and repeats that until it reaches the end. It requires either
preallocated heap or may fail under memory pressure, while unlikely to
be problematic, the complexity is O(N^2), and in general just nasty.
We're gonna convert all css_scan_users() to
css_task_iter_start/next/end() and remove css_scan_users(). As
css_scan_tasks() users may block, let's convert css_set_lock to a
rwsem so that tasks can block during css_task_iter_*() is in progress.
While this does increase the chance of possible deadlock scenarios,
given the current usage, the probability is relatively low, and even
if that happens, the right thing to do is updating the iteration in
the similar way to css iterators so that it can handle blocking.
Most conversions are trivial; however, task_cgroup_path() now expects
to be called with css_set_rwsem locked instead of locking itself.
This is because the function is called with RCU read lock held and
rwsem locking should nest outside RCU read lock.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Tejun Heo [Thu, 13 Feb 2014 11:58:39 +0000 (06:58 -0500)]
cgroup: reimplement cgroup_transfer_tasks() without using css_scan_tasks()
Reimplement cgroup_transfer_tasks() so that it repeatedly fetches the
first task in the cgroup and then tranfers it. This achieves the same
result without using css_scan_tasks() which is scheduled to be
removed.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Tejun Heo [Thu, 13 Feb 2014 11:58:39 +0000 (06:58 -0500)]
cgroup: implement cgroup_has_tasks() and unexport cgroup_task_count()
cgroup_task_count() read-locks css_set_lock and walks all tasks to
count them and then returns the result. The only thing all the users
want is determining whether the cgroup is empty or not. This patch
implements cgroup_has_tasks() which tests whether cgroup->cset_links
is empty, replaces all cgroup_task_count() usages and unexports it.
Note that the test isn't synchronized. This is the same as before.
The test has always been racy.
This will help planned css_set locking update.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com> Acked-by: Michal Hocko <mhocko@suse.cz> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Balbir Singh <bsingharora@gmail.com> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Tejun Heo [Thu, 13 Feb 2014 11:58:38 +0000 (06:58 -0500)]
cgroup: enable task_cg_lists on the first cgroup mount
Tasks are not linked on their css_sets until cgroup task iteration is
actually used. This is to avoid incurring overhead on the fork and
exit paths for systems which have cgroup compiled in but don't use it.
This lazy binding also affects the task migration path. It has to be
careful so that it doesn't link tasks to css_sets when task_cg_lists
linking is not enabled yet. Unfortunately, this conditional linking
in the migration path interferes with planned migration updates.
This patch moves the lazy binding a bit earlier, to the first cgroup
mount. It's a clear indication that cgroup is being used on the
system and task_cg_lists linking is highly likely to be enabled soon
anyway through "tasks" and "cgroup.procs" files.
This allows cgroup_task_migrate() to always link @tsk->cg_list. Note
that it may still race with cgroup_post_fork() but who wins that race
is inconsequential.
While at it, make use_task_css_set_links a bool, add sanity checks in
cgroup_enable_task_cg_lists() and css_task_iter_start(), and update
the former so that it's guaranteed and assumes to run only once.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Tejun Heo [Thu, 13 Feb 2014 11:58:38 +0000 (06:58 -0500)]
cgroup: drop CGRP_ROOT_SUBSYS_BOUND
Before kernfs conversion, due to the way super_block lookup works,
cgroup roots were created and made visible before being fully
initialized. This in turn required a special flag to mark that the
root hasn't been fully initialized so that the destruction path can
tell fully bound ones from half initialized.
That flag is CGRP_ROOT_SUBSYS_BOUND and no longer necessary after the
kernfs conversion as the lookup and creation of new root are atomic
w.r.t. cgroup_mutex. This patch removes the flag and passes the
requests subsystem mask to cgroup_setup_root() so that it can set the
respective mask bits as subsystems are bound.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
It's because more thorough testing, by others here, found that it
wasn't always solving the problem: so I asked Tejun privately to
hold off from sending it in, until we'd worked out why not.
Most of our testing being on a v3,11-based kernel, it was perfectly
possible that the problem was merely our own e.g. missing Tejun's 8a2b75384444 ("workqueue: fix ordered workqueues in NUMA setups").
But that turned out not to be enough to fix it either. Then Filipe
pointed out how percpu_ref_kill_and_confirm() uses call_rcu_sched()
before we ever get to put the offline on to the workqueue: by the
time we get to the workqueue, the ordering has already been lost.
So, thanks for the Acks, but I'm afraid that this ordered workqueue
solution is just not good enough: we should simply forget that patch
and provide a different answer."
Tejun Heo [Wed, 12 Feb 2014 14:29:50 +0000 (09:29 -0500)]
cgroup: remove cgroupfs_root->refcnt
Currently, cgroupfs_root and its ->top_cgroup are separated reference
counted and the latter's is ignored. There's no reason to do this
separately. This patch removes cgroupfs_root->refcnt and destroys
cgroupfs_root when the top_cgroup is released.
* cgroup_put() updated to ignore cgroup_is_dead() test for top
cgroups. cgroup_free_fn() updated to handle root destruction when
releasing a top cgroup.
* As root destruction is now bounced through cgroup destruction, it is
asynchronous. Update cgroup_mount() so that it waits for pending
release which is currently implemented using msleep(). Converting
this to proper wait_queue isn't hard but likely unnecessary.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Tejun Heo [Wed, 12 Feb 2014 14:29:50 +0000 (09:29 -0500)]
cgroup: rename cgroupfs_root->number_of_cgroups to ->nr_cgrps and make it atomic_t
root->number_of_cgroups is currently an integer protected with
cgroup_mutex. Except for sanity checks and proc reporting, the only
place it's used is to check whether the root has any child during
remount; however, this is a bit flawed as the counter is not
decremented when the cgroup is unlinked but when it's released,
meaning that there could be an extended period where all cgroups are
removed but remount is still not allowed because some internal objects
are lingering. While not perfect either, it'd be better to use
emptiness test on root->top_cgroup.children.
This patch updates cgroup_remount() to test top_cgroup's children
instead, which makes number_of_cgroups only actual usage statistics
printing in proc implemented in proc_cgroupstats_show(). Let's
shorten its name and make it an atomic_t so that we don't have to
worry about its synchronization. It's purely auxiliary at this point.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Tejun Heo [Wed, 12 Feb 2014 14:29:50 +0000 (09:29 -0500)]
cgroup: remove cgroup->name
cgroup->name handling became quite complicated over time involving
dedicated struct cgroup_name for RCU protection. Now that cgroup is
on kernfs, we can drop all of it and simply use kernfs_name/path() and
friends. Replace cgroup->name and all related code with kernfs
name/path constructs.
* Reimplement cgroup_name() and cgroup_path() as thin wrappers on top
of kernfs counterparts, which involves semantic changes.
pr_cont_cgroup_name() and pr_cont_cgroup_path() added.
* cgroup->name handling dropped from cgroup_rename().
* All users of cgroup_name/path() updated to the new semantics. Users
which were formatting the string just to printk them are converted
to use pr_cont_cgroup_name/path() instead, which simplifies things
quite a bit. As cgroup_name() no longer requires RCU read lock
around it, RCU lockings which were protecting only cgroup_name() are
removed.
v2: Comment above oom_info_lock updated as suggested by Michal.
v3: dummy_top doesn't have a kn associated and
pr_cont_cgroup_name/path() ended up calling the matching kernfs
functions with NULL kn leading to oops. Test for NULL kn and
print "/" if so. This issue was reported by Fengguang Wu.
v4: Rebased on top of 0ab02ca8f887 ("cgroup: protect modifications to
cgroup_idr with cgroup_mutex").
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Peter Zijlstra <peterz@infradead.org> Acked-by: Michal Hocko <mhocko@suse.cz> Acked-by: Li Zefan <lizefan@huawei.com> Cc: Fengguang Wu <fengguang.wu@intel.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Balbir Singh <bsingharora@gmail.com> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Tejun Heo [Wed, 12 Feb 2014 14:29:50 +0000 (09:29 -0500)]
cgroup: make cgroup hold onto its kernfs_node
cgroup currently releases its kernfs_node when it gets removed. While
not buggy, this makes cgroup->kn access rules complicated than
necessary and leads to things like get/put protection around
kernfs_remove() in cgroup_destroy_locked(). In addition, we want to
use kernfs_name/path() and friends but also want to be able to
determine a cgroup's name between removal and release.
This patch makes cgroup hold onto its kernfs_node until freed so that
cgroup->kn is always accessible.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Tejun Heo [Wed, 12 Feb 2014 14:29:49 +0000 (09:29 -0500)]
cgroup: simplify dynamic cftype addition and removal
Dynamic cftype addition and removal using cgroup_add/rm_cftypes()
respectively has been quite hairy due to vfs i_mutex. As i_mutex
nests outside cgroup_mutex, cgroup_mutex has to be released and
regrabbed on each iteration through the hierarchy complicating the
process. Now that i_mutex is no longer in play, it can be simplified.
* Just holding cgroup_tree_mutex is enough. No need to meddle with
cgroup_mutex.
* No reason to play the unlock - relock - check serial_nr dancing.
Everything can be atomically while holding cgroup_tree_mutex.
* cgroup_cfts_prepare() is replaced with direct locking of
cgroup_tree_mutex.
* cgroup_cfts_commit() no longer fiddles with locking. It just
applies the cftypes change to the existing cgroups in the hierarchy.
Renamed to cgroup_cfts_apply().
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Tejun Heo [Wed, 12 Feb 2014 14:29:48 +0000 (09:29 -0500)]
cgroup: remove cftype_set
cftype_set was added primarily to allow registering the same cftype
array more than once for different subsystems. Nobody uses or needs
such thing and it's already broken because each cftype has ->ss
pointer which is initialized during registration.
Let's add list_head ->node to cftype and use the first cftype entry in
the array to link them instead of allocating separate cftype_set.
While at it, trigger WARN if cft seems previously initialized during
registration.
This simplifies cftype handling a bit.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Tejun Heo [Wed, 12 Feb 2014 14:29:48 +0000 (09:29 -0500)]
cgroup: warn if "xattr" is specified with "sane_behavior"
Mount option "xattr" is no longer necessary as it's enabled by default
on kernfs. Warn if "xattr" is specified with "sane_behavior" so that
the option can be removed in the future.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Tejun Heo [Tue, 11 Feb 2014 16:52:49 +0000 (11:52 -0500)]
cgroup: convert to kernfs
cgroup filesystem code was derived from the original sysfs
implementation which was heavily intertwined with vfs objects and
locking with the goal of re-using the existing vfs infrastructure.
That experiment turned out rather disastrous and sysfs switched, a
long time ago, to distributed filesystem model where a separate
representation is maintained which is queried by vfs. Unfortunately,
cgroup stuck with the failed experiment all these years and
accumulated even more problems over time.
Locking and object lifetime management being entangled with vfs is
probably the most egregious. vfs is never designed to be misused like
this and cgroup ends up jumping through various convoluted dancing to
make things work. Even then, operations across multiple cgroups can't
be done safely as it'll deadlock with rename locking.
Recently, kernfs is separated out from sysfs so that it can be used by
users other than sysfs. This patch converts cgroup to use kernfs,
which will bring the following benefits.
* Separation from vfs internals. Locking and object lifetime
management is contained in cgroup proper making things a lot
simpler. This removes significant amount of locking convolutions,
hairy object lifetime rules and the restriction on multi-cgroup
operations.
* Can drop a lot of code to implement filesystem interface as most are
provided by kernfs.
* Proper "severing" semantics, which allows controllers to not worry
about lingering file accesses after offline.
While the preceding patches did as much as possible to make the
transition less painful, large part of the conversion has to be one
discrete step making this patch rather large. The rest of the commit
message lists notable changes in different areas.
* All dentry accessors are removed. Helpers to map from kernfs
constructs are added.
* All vfs plumbing around dentry, inode and bdi removed.
* cgroup_mount() now directly looks for matching root and then
proceeds to create a new one if not found.
Synchronization and object lifetime
-----------------------------------
* vfs inode locking removed. Among other things, this removes the
need for the convolution in cgroup_cfts_commit(). Future patches
will further simplify it.
* vfs refcnting replaced with cgroup internal ones. cgroup->refcnt,
cgroupfs_root->refcnt added. cgroup_put_root() now directly puts
root->refcnt and when it reaches zero proceeds to destroy it thus
merging cgroup_put_root() and the former cgroup_kill_sb().
Simliarly, cgroup_put() now directly schedules cgroup_free_rcu()
when refcnt reaches zero.
* Unlike before, kernfs objects don't hold onto cgroup objects. When
cgroup destroys a kernfs node, all existing operations are drained
and the association is broken immediately. The same for
cgroupfs_roots and mounts.
* All operations which come through kernfs guarantee that the
associated cgroup is and stays valid for the duration of operation;
however, there are two paths which need to find out the associated
cgroup from dentry without going through kernfs -
css_tryget_from_dir() and cgroupstats_build(). For these two,
kernfs_node->priv is RCU managed so that they can dereference it
under RCU read lock.
File and directory handling
---------------------------
* File and directory operations converted to kernfs_ops and
kernfs_syscall_ops.
* xattrs is implicitly supported by kernfs. No need to worry about it
from cgroup. This means that "xattr" mount option is no longer
necessary. A future patch will add a deprecated warning message
when sane_behavior.
* When cftype->max_write_len > PAGE_SIZE, it's necessary to make a
private copy of one of the kernfs_ops to set its atomic_write_len.
cftype->kf_ops is added and cgroup_init/exit_cftypes() are updated
to handle it.
* cftype->lockdep_key added so that kernfs lockdep annotation can be
per cftype.
* Inidividual file entries and open states are now managed by kernfs.
No need to worry about them from cgroup. cfent, cgroup_open_file
and their friends are removed.
* kernfs_nodes are created deactivated and kernfs_activate()
invocations added to places where creation of new nodes are
committed.
* cgroup_rmdir() uses kernfs_[un]break_active_protection() for
self-removal.
v2: - Li pointed out in an earlier patch that specifying "name="
during mount without subsystem specification should succeed if
there's an existing hierarchy with a matching name although it
should fail with -EINVAL if a new hierarchy should be created.
Prior to the conversion, this used by handled by deferring
failure from NULL return from cgroup_root_from_opts(), which was
necessary because root was being created before checking for
existing ones. Note that cgroup_root_from_opts() returned an
ERR_PTR() value for error conditions which require immediate
mount failure.
As we now have separate search and creation steps, deferring
failure from cgroup_root_from_opts() is no longer necessary.
cgroup_root_from_opts() is updated to always return ERR_PTR()
value on failure.
- The logic to match existing roots is updated so that a mount
attempt with a matching name but different subsys_mask are
rejected. This was handled by a separate matching loop under
the comment "Check for name clashes with existing mounts" but
got lost during conversion. Merge the check into the main
search loop.
- Add __rcu __force casting in RCU_INIT_POINTER() in
cgroup_destroy_locked() to avoid the sparse address space
warning reported by kbuild test bot. Maybe we want an explicit
interface to use kn->priv as RCU protected pointer?
v3: Make CONFIG_CGROUPS select CONFIG_KERNFS.
v4: Rebased on top of 0ab02ca8f887 ("cgroup: protect modifications to
cgroup_idr with cgroup_mutex").
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com> Cc: kbuild test robot fengguang.wu@intel.com>
Tejun Heo [Tue, 11 Feb 2014 16:52:49 +0000 (11:52 -0500)]
cgroup: introduce cgroup_ino()
mm/memory-failure.c::hwpoison_filter_task() has been reaching into
cgroup to extract the associated ino to be used as a filtering
criterion. This is an implementation detail which shouldn't be
depended upon from outside cgroup proper and is about to change with
the scheduled kernfs conversion.
This patch introduces a proper interface to determine the associated
ino, cgroup_ino(), and updates hwpoison_filter_task() to use it
instead of reaching directly into cgroup.
Tejun Heo [Tue, 11 Feb 2014 16:52:48 +0000 (11:52 -0500)]
cgroup: introduce cgroup_init/exit_cftypes()
Factor out cft->ss initialization into cgroup_init_cftypes() from
cgroup_add_cftypes() and add cft->ss clearing to cgroup_rm_cftypes()
through cgroup_exit_cftypes().
This doesn't make any meaningful difference now but the two new
functions will be expanded during kernfs transition.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Tejun Heo [Tue, 11 Feb 2014 16:52:48 +0000 (11:52 -0500)]
cgroup: update the meaning of cftype->max_write_len
cftype->max_write_len is used to extend the maximum size of writes.
It's interpreted in such a way that the actual maximum size is one
less than the specified value. The default size is defined by
CGROUP_LOCAL_BUFFER_SIZE. Its interpretation is quite confusing - its
value is decremented by 1 and then compared for equality with max
size, which means that the actual default size is
CGROUP_LOCAL_BUFFER_SIZE - 2, which is 62 chars.
There's no point in having a limit that low. Update its definition so
that it means the actual string length sans termination and anything
below PAGE_SIZE-1 is treated as PAGE_SIZE-1.
.max_write_len for "release_agent" is updated to PATH_MAX-1 and
cgroup_release_agent_write() is updated so that the redundant strlen()
check is removed and it uses strlcpy() instead of strcpy().
.max_write_len initializations in blk-throttle.c and cfq-iosched.c are
no longer necessary and removed. The one in cpuset is kept unchanged
as it's an approximated value to begin with.
This will also make transition to kernfs smoother.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Tejun Heo [Tue, 11 Feb 2014 16:52:48 +0000 (11:52 -0500)]
cgroup: make cgroup_subsys->base_cftypes use cgroup_add_cftypes()
Currently, cgroup_subsys->base_cftypes registration is different from
dynamic cftypes registartion. Instead of going through
cgroup_add_cftypes(), cgroup_init_subsys() invokes
cgroup_init_cftsets() which makes use of cgroup_subsys->base_cftset
which doesn't involve dynamic allocation.
While avoiding dynamic allocation is somewhat nice, having two
separate paths for cftypes registration is nasty, especially as we're
planning to add more operations during cftypes registration.
This patch drops cgroup_init_cftsets() and cgroup_subsys->base_cftset
and registers base_cftypes using cgroup_add_cftypes(). This is done
as a separate step in cgroup_init() instead of a part of
cgroup_init_subsys(). This is because cgroup_init_subsys() can be
called very early during boot when kmalloc() isn't available yet.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Tejun Heo [Tue, 11 Feb 2014 16:52:48 +0000 (11:52 -0500)]
cgroup: restructure locking and error handling in cgroup_mount()
cgroup is scheduled to be converted to kernfs. After conversion,
cgroup_mount() won't use the sget() machinery for finding out existing
super_blocks but instead would do that directly. It'll search the
existing cgroupfs_roots for a matching one and create a new one iff a
match doesn't exist. To ease such conversion, this patch restructures
locking and error handling of the function.
cgroup_tree_mutex and cgroup_mutex are grabbed from the get-go and
held until return. For now, due to the way vfs locks nest outside
cgroup mutexes, the two cgroup mutexes are temporarily dropped across
sget() and inode mutex locking, which looks quite ridiculous; however,
these will be removed through kernfs conversion and structuring the
code this way makes the conversion less painful.
The error goto labels are consolidated to two. This looks unwieldy
now but the next patch will factor out creation of new root into a
separate function with accompanying error handling and it'll look a
lot better.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Tejun Heo [Tue, 11 Feb 2014 16:52:47 +0000 (11:52 -0500)]
cgroup: release cgroup_mutex over file removals
Now that cftypes and all tree modification operations are protected by
cgroup_tree_mutex, we can drop cgroup_mutex while deleting files and
directories. Drop cgroup_mutex over removals.
This doesn't make any noticeable difference now but is to help kernfs
conversion. In kernfs, removals are sync points which drain in-flight
operations as those operations would grab cgroup_mutex, trying to
delete under cgroup_mutex would deadlock. This can be resolved by
just holding the outer cgroup_tree_mutex which nests outside both
kernfs active reference and cgroup_mutex.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Tejun Heo [Tue, 11 Feb 2014 16:52:47 +0000 (11:52 -0500)]
cgroup: introduce cgroup_tree_mutex
Currently cgroup uses combination of inode->i_mutex'es and
cgroup_mutex for synchronization. With the scheduled kernfs
conversion, i_mutex'es will be removed. Unfortunately, just using
cgroup_mutex isn't possible. All kernfs file and syscall operations,
most of which require grabbing cgroup_mutex, will be called with
kernfs active ref held and, if we try to perform kernfs removals under
cgroup_mutex, it can deadlock as kernfs_remove() tries to drain the
target node.
Let's introduce a new outer mutex, cgroup_tree_mutex, which protects
stuff used during hierarchy changing operations - cftypes and all the
operations which may affect the cgroupfs. It also covers css
association and iteration. This allows cgroup_css(), for_each_css()
and other css iterators to be called under cgroup_tree_mutex. The new
mutex will nest above both kernfs's active ref protection and
cgroup_mutex. By protecting tree modifications with a separate outer
mutex, we can get rid of the forementioned deadlock condition.
Actual file additions and removals now require cgroup_tree_mutex
instead of cgroup_mutex. Currently, cgroup_tree_mutex is never used
without cgroup_mutex; however, we'll soon add hierarchy modification
sections which are only protected by cgroup_tree_mutex. In the
future, we might want to make the locking more granular by better
splitting the coverages of the two mutexes. For now, this should do.
v2: Rebased on top of 0ab02ca8f887 ("cgroup: protect modifications to
cgroup_idr with cgroup_mutex").
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Tejun Heo [Tue, 11 Feb 2014 16:52:47 +0000 (11:52 -0500)]
cgroup: improve css_from_dir() into css_tryget_from_dir()
css_from_dir() returns the matching css (cgroup_subsys_state) given a
dentry and subsystem. The function doesn't pin the css before
returning and requires the caller to be holding RCU read lock or
cgroup_mutex and handling pinning on the caller side.
Given that users of the function are likely to want to pin the
returned css (both existing users do) and that getting and putting
css's are very cheap, there's no reason for the interface to be tricky
like this.
Rename css_from_dir() to css_tryget_from_dir() and make it try to pin
the found css and return it only if pinning succeeded. The callers
are updated so that they no longer do RCU locking and pinning around
the function and just use the returned css.
This will also ease converting cgroup to kernfs.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Michal Hocko <mhocko@suse.cz> Acked-by: Li Zefan <lizefan@huawei.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Balbir Singh <bsingharora@gmail.com> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Tejun Heo [Tue, 11 Feb 2014 16:02:59 +0000 (11:02 -0500)]
Merge branch 'cgroup/for-3.14-fixes' into cgroup/for-3.15
Pull for-3.14-fixes to receive 0ab02ca8f887 ("cgroup: protect
modifications to cgroup_idr with cgroup_mutex") prior to kernfs
conversion series to avoid non-trivial conflicts.
Li Zefan [Tue, 11 Feb 2014 08:05:46 +0000 (16:05 +0800)]
cgroup: protect modifications to cgroup_idr with cgroup_mutex
Setup cgroupfs like this:
# mount -t cgroup -o cpuacct xxx /cgroup
# mkdir /cgroup/sub1
# mkdir /cgroup/sub2
Then run these two commands:
# for ((; ;)) { mkdir /cgroup/sub1/tmp && rmdir /mnt/sub1/tmp; } &
# for ((; ;)) { mkdir /cgroup/sub2/tmp && rmdir /mnt/sub2/tmp; } &
It's because allocating/removing cgroup ID is not properly synchronized.
The bug was introduced when we converted cgroup_ida to cgroup_idr.
While synchronization is already done inside ida_simple_{get,remove}(),
users are responsible for concurrent calls to idr_{alloc,remove}().
tj: Refreshed on top of b58c89986a77 ("cgroup: fix error return from
cgroup_create()").
Fixes: 4e96ee8e981b ("cgroup: convert cgroup_ida to cgroup_idr") Cc: <stable@vger.kernel.org> #3.12+ Reported-by: Michal Hocko <mhocko@suse.cz> Signed-off-by: Li Zefan <lizefan@huawei.com> Signed-off-by: Tejun Heo <tj@kernel.org>
Tejun Heo [Sat, 8 Feb 2014 15:37:01 +0000 (10:37 -0500)]
cgroup: remove cgroup_root_mutex
cgroup_root_mutex was added to avoid deadlock involving namespace_sem
via cgroup_show_options(). It added a lot of overhead for the small
purpose of it and, because it's nested under cgroup_mutex, it has very
limited usefulness. The previous patch made cgroup_show_options() not
use cgroup_root_mutex, so nobody needs it anymore. Remove it.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Tejun Heo [Sat, 8 Feb 2014 15:36:58 +0000 (10:36 -0500)]
cgroup: update locking in cgroup_show_options()
cgroup_show_options() grabs cgroup_root_mutex to protect the options
changing while printing; however, holding root_mutex or not doesn't
really make much difference for the function. subsys_mask can be
atomically tested and most of the options aren't allowed to change
anyway once mounted.
The only field which needs synchronization is ->release_agent_path.
This patch introduces a dedicated spinlock to synchronize accesses to
the field and drops cgroup_root_mutex locking from
cgroup_show_options(). The next patch will remove cgroup_root_mutex.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Tejun Heo [Sat, 8 Feb 2014 15:36:58 +0000 (10:36 -0500)]
cgroup: clean up cgroup_subsys names and initialization
cgroup_subsys is a bit messier than it needs to be.
* The name of a subsys can be different from its internal identifier
defined in cgroup_subsys.h. Most subsystems use the matching name
but three - cpu, memory and perf_event - use different ones.
* cgroup_subsys_id enums are postfixed with _subsys_id and each
cgroup_subsys is postfixed with _subsys. cgroup.h is widely
included throughout various subsystems, it doesn't and shouldn't
have claim on such generic names which don't have any qualifier
indicating that they belong to cgroup.
* cgroup_subsys->subsys_id should always equal the matching
cgroup_subsys_id enum; however, we require each controller to
initialize it and then BUG if they don't match, which is a bit
silly.
This patch cleans up cgroup_subsys names and initialization by doing
the followings.
* cgroup_subsys_id enums are now postfixed with _cgrp_id, and each
cgroup_subsys with _cgrp_subsys.
* With the above, renaming subsys identifiers to match the userland
visible names doesn't cause any naming conflicts. All non-matching
identifiers are renamed to match the official names.
cpu_cgroup -> cpu
mem_cgroup -> memory
perf -> perf_event
* controllers no longer need to initialize ->subsys_id and ->name.
They're generated in cgroup core and set automatically during boot.
* Redundant cgroup_subsys declarations removed.
* While updating BUG_ON()s in cgroup_init_early(), convert them to
WARN()s. BUGging that early during boot is stupid - the kernel
can't print anything, even through serial console and the trap
handler doesn't even link stack frame properly for back-tracing.
This patch doesn't introduce any behavior changes.
v2: Rebased on top of fe1217c4f3f7 ("net: net_cls: move cgroupfs
classid handling into core").
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Neil Horman <nhorman@tuxdriver.com> Acked-by: "David S. Miller" <davem@davemloft.net> Acked-by: "Rafael J. Wysocki" <rjw@rjwysocki.net> Acked-by: Michal Hocko <mhocko@suse.cz> Acked-by: Peter Zijlstra <peterz@infradead.org> Acked-by: Aristeu Rozanski <aris@redhat.com> Acked-by: Ingo Molnar <mingo@redhat.com> Acked-by: Li Zefan <lizefan@huawei.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Balbir Singh <bsingharora@gmail.com> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Serge E. Hallyn <serue@us.ibm.com> Cc: Vivek Goyal <vgoyal@redhat.com> Cc: Thomas Graf <tgraf@suug.ch>
Tejun Heo [Sat, 8 Feb 2014 15:36:58 +0000 (10:36 -0500)]
cgroup: drop module support
With module supported dropped from net_prio, no controller is using
cgroup module support. None of actual resource controllers can be
built as a module and we aren't gonna add new controllers which don't
control resources. This patch drops module support from cgroup.
* cgroup_[un]load_subsys() and cgroup_subsys->module removed.
* As there's no point in distinguishing IS_BUILTIN() and IS_MODULE(),
cgroup_subsys.h now uses IS_ENABLED() directly.
* enum cgroup_subsys_id now exactly matches the list of enabled
controllers as ordered in cgroup_subsys.h.
* cgroup_subsys[] is now a contiguously occupied array. Size
specification is no longer necessary and dropped.
* for_each_builtin_subsys() is removed and for_each_subsys() is
updated to not require any locking.
* module ref handling is removed from rebind_subsystems().
* Module related comments dropped.
v2: Rebased on top of fe1217c4f3f7 ("net: net_cls: move cgroupfs
classid handling into core").
v3: Added {} around the if (need_forkexit_callback) block in
cgroup_post_fork() for readability as suggested by Li.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Tejun Heo [Sat, 8 Feb 2014 15:36:58 +0000 (10:36 -0500)]
cgroup: make CONFIG_CGROUP_NET_PRIO bool and drop unnecessary init_netclassid_cgroup()
net_prio is the only cgroup which is allowed to be built as a module.
The savings from allowing one controller to be built as a module are
tiny especially given that cgroup module support itself adds quite a
bit of complexity.
Given that none of other controllers has much chance of being made a
module and that we're unlikely to add new modular controllers, the
added complexity is simply not justifiable.
As a first step to drop cgroup module support, this patch changes the
config option to bool from tristate and drops module related code from
it.
Also, while an earlier commit fe1217c4f3f7 ("net: net_cls: move
cgroupfs classid handling into core") dropped module support from
net_cls cgroup, it retained a call to cgroup_load_subsys(), which is
noop for built-in controllers. Drop it along with
init_netclassid_cgroup().
v2: Removed modular version of task_netprioidx() in
include/net/netprio_cgroup.h as suggested by Li Zefan.
v3: Rebased on top of fe1217c4f3f7 ("net: net_cls: move cgroupfs
classid handling into core"). net_cls cgroup part is mostly
dropped except for removal of init_netclassid_cgroup().
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Neil Horman <nhorman@tuxdriver.com> Acked-by: "David S. Miller" <davem@davemloft.net> Acked-by: Li Zefan <lizefan@huawei.com> Cc: Thomas Graf <tgraf@suug.ch>
Tejun Heo [Sat, 8 Feb 2014 15:26:34 +0000 (10:26 -0500)]
cgroup: fix locking in cgroup_cfts_commit()
cgroup_cfts_commit() walks the cgroup hierarchy that the target
subsystem is attached to and tries to apply the file changes. Due to
the convolution with inode locking, it can't keep cgroup_mutex locked
while iterating. It currently holds only RCU read lock around the
actual iteration and then pins the found cgroup using dget().
Unfortunately, this is incorrect. Although the iteration does check
cgroup_is_dead() before invoking dget(), there's nothing which
prevents the dentry from going away inbetween. Note that this is
different from the usual css iterations where css_tryget() is used to
pin the css - css_tryget() tests whether the css can be pinned and
fails if not.
The problem can be solved by simply holding cgroup_mutex instead of
RCU read lock around the iteration, which actually reduces LOC.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com> Cc: stable@vger.kernel.org
Tejun Heo [Sat, 8 Feb 2014 15:26:33 +0000 (10:26 -0500)]
cgroup: fix error return value in cgroup_mount()
When cgroup_mount() fails to allocate an id for the root, it didn't
set ret before jumping to unlock_drop ending up returning 0 after a
failure. Fix it.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com> Cc: stable@vger.kernel.org
Tejun Heo [Mon, 3 Feb 2014 19:09:17 +0000 (14:09 -0500)]
kernfs: add CONFIG_KERNFS
As sysfs was kernfs's only user, kernfs has been piggybacking on
CONFIG_SYSFS; however, kernfs is scheduled to grow a new user very
soon. Introduce a separate config option CONFIG_KERNFS which is to be
selected by kernfs users.
Tejun Heo [Fri, 7 Feb 2014 18:32:07 +0000 (13:32 -0500)]
sysfs, kobject: add sysfs wrapper for kernfs_enable_ns()
Currently, kobject is invoking kernfs_enable_ns() directly. This is
fine now as sysfs and kernfs are enabled and disabled together. If
sysfs is disabled, kernfs_enable_ns() is switched to dummy
implementation too and everything is fine; however, kernfs will soon
have its own config option CONFIG_KERNFS and !SYSFS && KERNFS will be
possible, which can make kobject call into non-dummy
kernfs_enable_ns() with NULL kernfs_node pointers leading to an oops.
Introduce sysfs_enable_ns() which is a wrapper around
kernfs_enable_ns() so that it can be made a noop depending only on
CONFIG_SYSFS regardless of the planned CONFIG_KERNFS.
Tejun Heo [Fri, 7 Feb 2014 18:32:07 +0000 (13:32 -0500)]
kernfs: implement kernfs_get_parent(), kernfs_name/path() and friends
kernfs_node->parent and ->name are currently marked as "published"
indicating that kernfs users may access them directly; however, those
fields may get updated by kernfs_rename[_ns]() and unrestricted access
may lead to erroneous values or oops.
Protect ->parent and ->name updates with a irq-safe spinlock
kernfs_rename_lock and implement the following accessors for these
fields.
* kernfs_name() - format the node's name into the specified buffer
* kernfs_path() - format the node's path into the specified buffer
* pr_cont_kernfs_name() - pr_cont a node's name (doesn't need buffer)
* pr_cont_kernfs_path() - pr_cont a node's path (doesn't need buffer)
* kernfs_get_parent() - pin and return a node's parent
All can be called under any context. The recursive sysfs_pathname()
in fs/sysfs/dir.c is replaced with kernfs_path() and
sysfs_rename_dir_ns() is updated to use kernfs_get_parent() instead of
dereferencing parent directly.
v2: Dummy definition of kernfs_path() for !CONFIG_KERNFS was missing
static inline making it cause a lot of build warnings. Add it.
Tejun Heo [Mon, 3 Feb 2014 19:09:15 +0000 (14:09 -0500)]
kernfs: implement kernfs_node_from_dentry(), kernfs_root_from_sb() and kernfs_rename()
Implement helpers to determine node from dentry and root from
super_block. Also add a kernfs_rename_ns() wrapper which assumes NULL
namespace. These generally make sense and will be used by cgroup.
v2: Some dummy implementations for !CONFIG_SYSFS was missing. Fixed.
Reported by kbuild test robot.
Tejun Heo [Mon, 3 Feb 2014 19:09:13 +0000 (14:09 -0500)]
kernfs: implement kernfs_ops->atomic_write_len
A write to a kernfs_node is buffered through a kernel buffer. Writes
<= PAGE_SIZE are performed atomically, while larger ones are executed
in PAGE_SIZE chunks. While this is enough for sysfs, cgroup which is
scheduled to be converted to use kernfs needs a bit more control over
it.
This patch adds kernfs_ops->atomic_write_len. If not set (zero), the
behavior stays the same. If set, writes upto the size are executed
atomically and larger writes are rejected with -E2BIG.
A different implementation strategy would be allowing configuring
chunking size while making the original write size available to the
write method; however, such strategy, while being more complicated,
doesn't really buy anything. If the write implementation has to
handle chunking, the specific chunk size shouldn't matter all that
much.
Tejun Heo [Mon, 3 Feb 2014 19:09:12 +0000 (14:09 -0500)]
kernfs: allow nodes to be created in the deactivated state
Currently, kernfs_nodes are made visible to userland on creation,
which makes it difficult for kernfs users to atomically succeed or
fail creation of multiple nodes. In addition, if something fails
after creating some nodes, the created nodes might already be in use
and their active refs need to be drained for removal, which has the
potential to introduce tricky reverse locking dependency on active_ref
depending on how the error path is synchronized.
This patch introduces per-root flag KERNFS_ROOT_CREATE_DEACTIVATED.
If set, all nodes under the root are created in the deactivated state
and stay invisible to userland until explicitly enabled by the new
kernfs_activate() API. Also, nodes which have never been activated
are guaranteed to bypass draining on removal thus allowing error paths
to not worry about lockding dependency on active_ref draining.
Tejun Heo [Mon, 3 Feb 2014 19:09:11 +0000 (14:09 -0500)]
kernfs: add missing kernfs_active() checks in directory operations
kernfs_iop_lookup(), kernfs_dir_pos() and kernfs_dir_next_pos() were
missing kernfs_active() tests before using the found kernfs_node. As
deactivated state is currently visible only while a node is being
removed, this doesn't pose an actual problem. e.g. lookup succeeding
on a deactivated node doesn't harm anything as the eventual file
operations are gonna fail and those failures are indistinguishible
from the cases in which the lookups had happened before the node was
deactivated.
However, we're gonna allow new nodes to be created deactivated and
then activated explicitly by the kernfs user when it sees fit. This
is to support atomically making multiple nodes visible to userland and
thus those nodes must not be visible to userland before activated.
Let's plug the lookup and readdir holes so that deactivated nodes are
invisible to userland.
Tejun Heo [Mon, 3 Feb 2014 19:09:10 +0000 (14:09 -0500)]
kernfs: implement kernfs_syscall_ops->remount_fs() and ->show_options()
Add two super_block related syscall callbacks ->remount_fs() and
->show_options() to kernfs_syscall_ops. These simply forward the
matching super_operations.
Tejun Heo [Mon, 3 Feb 2014 19:09:08 +0000 (14:09 -0500)]
kernfs: invoke dir_ops while holding active ref of the target node
kernfs_dir_ops are currently being invoked without any active
reference, which makes it tricky for the invoked operations to
determine whether the objects associated those nodes are safe to
access and will remain that way for the duration of such operations.
kernfs already has active_ref mechanism to deal with this which makes
the removal of a given node the synchronization point for gating the
file operations. There's no reason for dir_ops to be any different.
Update the dir_ops handling so that active_ref is held while the
dir_ops are executing. This guarantees that while a dir_ops is
executing the target nodes stay alive.
As kernfs_dir_ops doesn't have any in-kernel user at this point, this
doesn't affect anybody.
Tejun Heo [Mon, 3 Feb 2014 19:03:04 +0000 (14:03 -0500)]
s390: use device_remove_file_self() instead of device_schedule_callback()
driver-core now supports synchrnous self-deletion of attributes and
the asynchrnous removal mechanism is scheduled for removal. Use it
instead of device_schedule_callback().
* Conversions in arch/s390/pci/pci_sysfs.c and
drivers/s390/block/dcssblk.c are straightforward.
* drivers/s390/cio/ccwgroup.c is a bit more tricky because
ccwgroup_notifier() was (ab)using device_schedule_callback() to
purely obtain a process context to kick off ungroup operation which
may block from a notifier callback.
Rename ccwgroup_ungroup_callback() to ccwgroup_ungroup() and make it
take ccwgroup_device * instead. The new function is now called
directly from ccwgroup_ungroup_store().
ccwgroup_notifier() chain is updated to explicitly bounce through
ccwgroup_device->ungroup_work. This also removes possible failure
from memory pressure.
Tejun Heo [Mon, 3 Feb 2014 19:03:03 +0000 (14:03 -0500)]
scsi: use device_remove_file_self() instead of device_schedule_callback()
driver-core now supports synchrnous self-deletion of attributes and
the asynchrnous removal mechanism is scheduled for removal. Use it
instead of device_schedule_callback(). This makes "delete" behave
synchronously.
Tejun Heo [Mon, 3 Feb 2014 19:03:02 +0000 (14:03 -0500)]
pci: use device_remove_file_self() instead of device_schedule_callback()
driver-core now supports synchrnous self-deletion of attributes and
the asynchrnous removal mechanism is scheduled for removal. Use it
instead of device_schedule_callback(). This makes "remove" behave
synchronously.
Tejun Heo [Mon, 3 Feb 2014 19:03:01 +0000 (14:03 -0500)]
kernfs, sysfs, driver-core: implement kernfs_remove_self() and its wrappers
Sometimes it's necessary to implement a node which wants to delete
nodes including itself. This isn't straightforward because of kernfs
active reference. While a file operation is in progress, an active
reference is held and kernfs_remove() waits for all such references to
drain before completing. For a self-deleting node, this is a deadlock
as kernfs_remove() ends up waiting for an active reference that itself
is sitting on top of.
This currently is worked around in the sysfs layer using
sysfs_schedule_callback() which makes such removals asynchronous.
While it works, it's rather cumbersome and inherently breaks
synchronicity of the operation - the file operation which triggered
the operation may complete before the removal is finished (or even
started) and the removal may fail asynchronously. If a removal
operation is immmediately followed by another operation which expects
the specific name to be available (e.g. removal followed by rename
onto the same name), there's no way to make the latter operation
reliable.
The thing is there's no inherent reason for this to be asynchrnous.
All that's necessary to do this synchronous is a dedicated operation
which drops its own active ref and deactivates self. This patch
implements kernfs_remove_self() and its wrappers in sysfs and driver
core. kernfs_remove_self() is to be called from one of the file
operations, drops the active ref the task is holding, removes the self
node, and restores active ref to the dead node so that the ref is
balanced afterwards. __kernfs_remove() is updated so that it takes an
early exit if the target node is already fully removed so that the
active ref restored by kernfs_remove_self() after removal doesn't
confuse the deactivation path.
This makes implementing self-deleting nodes very easy. The normal
removal path doesn't even need to be changed to use
kernfs_remove_self() for the self-deleting node. The method can
invoke kernfs_remove_self() on itself before proceeding the normal
removal path. kernfs_remove() invoked on the node by the normal
deletion path will simply be ignored.
This will replace sysfs_schedule_callback(). A subtle feature of
sysfs_schedule_callback() is that it collapses multiple invocations -
even if multiple removals are triggered, the removal callback is run
only once. An equivalent effect can be achieved by testing the return
value of kernfs_remove_self() - only the one which gets %true return
value should proceed with actual deletion. All other instances of
kernfs_remove_self() will wait till the enclosing kernfs operation
which invoked the winning instance of kernfs_remove_self() finishes
and then return %false. This trivially makes all users of
kernfs_remove_self() automatically show correct synchronous behavior
even when there are multiple concurrent operations - all "echo 1 >
delete" instances will finish only after the whole operation is
completed by one of the instances.
Note that manipulation of active ref is implemented in separate public
functions - kernfs_[un]break_active_protection().
kernfs_remove_self() is the only user at the moment but this will be
used to cater to more complex cases.
v2: For !CONFIG_SYSFS, dummy version kernfs_remove_self() was missing
and sysfs_remove_file_self() had incorrect return type. Fix it.
Reported by kbuild test bot.
v3: kernfs_[un]break_active_protection() separated out from
kernfs_remove_self() and exposed as public API.
Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Alan Stern <stern@rowland.harvard.edu> Cc: kbuild test robot <fengguang.wu@intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Tejun Heo [Mon, 3 Feb 2014 19:03:00 +0000 (14:03 -0500)]
kernfs: remove KERNFS_REMOVED
KERNFS_REMOVED is used to mark half-initialized and dying nodes so
that they don't show up in lookups and deny adding new nodes under or
renaming it; however, its role overlaps that of deactivation.
It's necessary to deny addition of new children while removal is in
progress; however, this role considerably intersects with deactivation
- KERNFS_REMOVED prevents new children while deactivation prevents new
file operations. There's no reason to have them separate making
things more complex than necessary.
This patch removes KERNFS_REMOVED.
* Instead of KERNFS_REMOVED, each node now starts its life
deactivated. This means that we now use both atomic_add() and
atomic_sub() on KN_DEACTIVATED_BIAS, which is INT_MIN. The compiler
generates an overflow warnings when negating INT_MIN as the negation
can't be represented as a positive number. Nothing is actually
broken but let's bump BIAS by one to avoid the warnings for archs
which negates the subtrahend..
* A new helper kernfs_active() which tests whether kn->active >= 0 is
added for convenience and lockdep annotation. All KERNFS_REMOVED
tests are replaced with negated kernfs_active() tests.
* __kernfs_remove() is updated to deactivate, but not drain, all nodes
in the subtree instead of setting KERNFS_REMOVED. This removes
deactivation from kernfs_deactivate(), which is now renamed to
kernfs_drain().
* Sanity check on KERNFS_REMOVED in kernfs_put() is replaced with
checks on the active ref.
* Some comment style updates in the affected area.
v2: Reordered before removal path restructuring. kernfs_active()
dropped and kernfs_get/put_active() used instead. RB_EMPTY_NODE()
used in the lookup paths.
v3: Reverted most of v2 except for creating a new node with
KN_DEACTIVATED_BIAS.
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