using RCU rather than SRCU, because RCU is almost always faster
and easier to use than is SRCU.
- If you need to enter your read-side critical section in a
- hardirq or exception handler, and then exit that same read-side
- critical section in the task that was interrupted, then you need
- to srcu_read_lock_raw() and srcu_read_unlock_raw(), which avoid
- the lockdep checking that would otherwise this practice illegal.
-
Also unlike other forms of RCU, explicit initialization
and cleanup is required via init_srcu_struct() and
cleanup_srcu_struct(). These are passed a "struct srcu_struct"
"srcu_expedited": srcu_read_lock(), srcu_read_unlock() and
synchronize_srcu_expedited().
- "srcu_raw": srcu_read_lock_raw(), srcu_read_unlock_raw(),
- and call_srcu().
-
- "srcu_raw_sync": srcu_read_lock_raw(), srcu_read_unlock_raw(),
- and synchronize_srcu().
-
"sched": preempt_disable(), preempt_enable(), and
call_rcu_sched().
reasons, e.g., the grace period ended first.
-CONFIG_TINY_RCU and CONFIG_TINY_PREEMPT_RCU debugfs Files and Formats
+CONFIG_TINY_RCU debugfs Files and Formats
These implementations of RCU provides a single debugfs file under the
top-level directory RCU, namely rcu/rcudata, which displays fields in
-rcu_bh_ctrlblk, rcu_sched_ctrlblk and, for CONFIG_TINY_PREEMPT_RCU,
-rcu_preempt_ctrlblk.
+rcu_bh_ctrlblk and rcu_sched_ctrlblk.
The output of "cat rcu/rcudata" is as follows:
-rcu_preempt: qlen=24 gp=1097669 g197/p197/c197 tasks=...
- ttb=. btg=no ntb=184 neb=0 nnb=183 j=01f7 bt=0274
- normal balk: nt=1097669 gt=0 bt=371 b=0 ny=25073378 nos=0
- exp balk: bt=0 nos=0
rcu_sched: qlen: 0
rcu_bh: qlen: 0
-This is split into rcu_preempt, rcu_sched, and rcu_bh sections, with the
-rcu_preempt section appearing only in CONFIG_TINY_PREEMPT_RCU builds.
-The last three lines of the rcu_preempt section appear only in
-CONFIG_RCU_BOOST kernel builds. The fields are as follows:
+This is split into rcu_sched and rcu_bh sections. The field is as
+follows:
o "qlen" is the number of RCU callbacks currently waiting either
for an RCU grace period or waiting to be invoked. This is the
only field present for rcu_sched and rcu_bh, due to the
short-circuiting of grace period in those two cases.
-
-o "gp" is the number of grace periods that have completed.
-
-o "g197/p197/c197" displays the grace-period state, with the
- "g" number being the number of grace periods that have started
- (mod 256), the "p" number being the number of grace periods
- that the CPU has responded to (also mod 256), and the "c"
- number being the number of grace periods that have completed
- (once again mode 256).
-
- Why have both "gp" and "g"? Because the data flowing into
- "gp" is only present in a CONFIG_RCU_TRACE kernel.
-
-o "tasks" is a set of bits. The first bit is "T" if there are
- currently tasks that have recently blocked within an RCU
- read-side critical section, the second bit is "N" if any of the
- aforementioned tasks are blocking the current RCU grace period,
- and the third bit is "E" if any of the aforementioned tasks are
- blocking the current expedited grace period. Each bit is "."
- if the corresponding condition does not hold.
-
-o "ttb" is a single bit. It is "B" if any of the blocked tasks
- need to be priority boosted and "." otherwise.
-
-o "btg" indicates whether boosting has been carried out during
- the current grace period, with "exp" indicating that boosting
- is in progress for an expedited grace period, "no" indicating
- that boosting has not yet started for a normal grace period,
- "begun" indicating that boosting has bebug for a normal grace
- period, and "done" indicating that boosting has completed for
- a normal grace period.
-
-o "ntb" is the total number of tasks subjected to RCU priority boosting
- periods since boot.
-
-o "neb" is the number of expedited grace periods that have had
- to resort to RCU priority boosting since boot.
-
-o "nnb" is the number of normal grace periods that have had
- to resort to RCU priority boosting since boot.
-
-o "j" is the low-order 16 bits of the jiffies counter in hexadecimal.
-
-o "bt" is the low-order 16 bits of the value that the jiffies counter
- will have at the next time that boosting is scheduled to begin.
-
-o In the line beginning with "normal balk", the fields are as follows:
-
- o "nt" is the number of times that the system balked from
- boosting because there were no blocked tasks to boost.
- Note that the system will balk from boosting even if the
- grace period is overdue when the currently running task
- is looping within an RCU read-side critical section.
- There is no point in boosting in this case, because
- boosting a running task won't make it run any faster.
-
- o "gt" is the number of times that the system balked
- from boosting because, although there were blocked tasks,
- none of them were preventing the current grace period
- from completing.
-
- o "bt" is the number of times that the system balked
- from boosting because boosting was already in progress.
-
- o "b" is the number of times that the system balked from
- boosting because boosting had already completed for
- the grace period in question.
-
- o "ny" is the number of times that the system balked from
- boosting because it was not yet time to start boosting
- the grace period in question.
-
- o "nos" is the number of times that the system balked from
- boosting for inexplicable ("not otherwise specified")
- reasons. This can actually happen due to races involving
- increments of the jiffies counter.
-
-o In the line beginning with "exp balk", the fields are as follows:
-
- o "bt" is the number of times that the system balked from
- boosting because there were no blocked tasks to boost.
-
- o "nos" is the number of times that the system balked from
- boosting for inexplicable ("not otherwise specified")
- reasons.
srcu_read_lock synchronize_srcu srcu_barrier
srcu_read_unlock call_srcu
- srcu_read_lock_raw synchronize_srcu_expedited
- srcu_read_unlock_raw
- srcu_dereference
+ srcu_dereference synchronize_srcu_expedited
SRCU: Initialization/cleanup
init_srcu_struct
a. Will readers need to block? If so, you need SRCU.
-b. Is it necessary to start a read-side critical section in a
- hardirq handler or exception handler, and then to complete
- this read-side critical section in the task that was
- interrupted? If so, you need SRCU's srcu_read_lock_raw() and
- srcu_read_unlock_raw() primitives.
-
-c. What about the -rt patchset? If readers would need to block
+b. What about the -rt patchset? If readers would need to block
in an non-rt kernel, you need SRCU. If readers would block
in a -rt kernel, but not in a non-rt kernel, SRCU is not
necessary.
-d. Do you need to treat NMI handlers, hardirq handlers,
+c. Do you need to treat NMI handlers, hardirq handlers,
and code segments with preemption disabled (whether
via preempt_disable(), local_irq_save(), local_bh_disable(),
or some other mechanism) as if they were explicit RCU readers?
If so, RCU-sched is the only choice that will work for you.
-e. Do you need RCU grace periods to complete even in the face
+d. Do you need RCU grace periods to complete even in the face
of softirq monopolization of one or more of the CPUs? For
example, is your code subject to network-based denial-of-service
attacks? If so, you need RCU-bh.
-f. Is your workload too update-intensive for normal use of
+e. Is your workload too update-intensive for normal use of
RCU, but inappropriate for other synchronization mechanisms?
If so, consider SLAB_DESTROY_BY_RCU. But please be careful!
-g. Do you need read-side critical sections that are respected
+f. Do you need read-side critical sections that are respected
even though they are in the middle of the idle loop, during
user-mode execution, or on an offlined CPU? If so, SRCU is the
only choice that will work for you.
-h. Otherwise, use RCU.
+g. Otherwise, use RCU.
Of course, this all assumes that you have determined that RCU is in fact
the right tool for your job.
calls and by forcing both kernel threads and interrupts
to execute elsewhere.
+Name: kworker/%u:%d%s (cpu, id, priority)
+Purpose: Execute workqueue requests
+To reduce its OS jitter, do any of the following:
+1. Run your workload at a real-time priority, which will allow
+ preempting the kworker daemons.
+2. Do any of the following needed to avoid jitter that your
+ application cannot tolerate:
+ a. Build your kernel with CONFIG_SLUB=y rather than
+ CONFIG_SLAB=y, thus avoiding the slab allocator's periodic
+ use of each CPU's workqueues to run its cache_reap()
+ function.
+ b. Avoid using oprofile, thus avoiding OS jitter from
+ wq_sync_buffer().
+ c. Limit your CPU frequency so that a CPU-frequency
+ governor is not required, possibly enlisting the aid of
+ special heatsinks or other cooling technologies. If done
+ correctly, and if you CPU architecture permits, you should
+ be able to build your kernel with CONFIG_CPU_FREQ=n to
+ avoid the CPU-frequency governor periodically running
+ on each CPU, including cs_dbs_timer() and od_dbs_timer().
+ WARNING: Please check your CPU specifications to
+ make sure that this is safe on your particular system.
+ d. It is not possible to entirely get rid of OS jitter
+ from vmstat_update() on CONFIG_SMP=y systems, but you
+ can decrease its frequency by writing a large value to
+ /proc/sys/vm/stat_interval. The default value is HZ,
+ for an interval of one second. Of course, larger values
+ will make your virtual-memory statistics update more
+ slowly. Of course, you can also run your workload at
+ a real-time priority, thus preempting vmstat_update().
+ e. If running on high-end powerpc servers, build with
+ CONFIG_PPC_RTAS_DAEMON=n. This prevents the RTAS
+ daemon from running on each CPU every second or so.
+ (This will require editing Kconfig files and will defeat
+ this platform's RAS functionality.) This avoids jitter
+ due to the rtas_event_scan() function.
+ WARNING: Please check your CPU specifications to
+ make sure that this is safe on your particular system.
+ f. If running on Cell Processor, build your kernel with
+ CBE_CPUFREQ_SPU_GOVERNOR=n to avoid OS jitter from
+ spu_gov_work().
+ WARNING: Please check your CPU specifications to
+ make sure that this is safe on your particular system.
+ g. If running on PowerMAC, build your kernel with
+ CONFIG_PMAC_RACKMETER=n to disable the CPU-meter,
+ avoiding OS jitter from rackmeter_do_timer().
+
Name: rcuc/%u
Purpose: Execute RCU callbacks in CONFIG_RCU_BOOST=y kernels.
To reduce its OS jitter, do at least one of the following:
some types of computationally intensive high-performance computing (HPC)
applications and for real-time applications.
-There are two main contexts in which the number of scheduling-clock
-interrupts can be reduced compared to the old-school approach of sending
-a scheduling-clock interrupt to all CPUs every jiffy whether they need
-it or not (CONFIG_HZ_PERIODIC=y or CONFIG_NO_HZ=n for older kernels):
+There are three main ways of managing scheduling-clock interrupts
+(also known as "scheduling-clock ticks" or simply "ticks"):
-1. Idle CPUs (CONFIG_NO_HZ_IDLE=y or CONFIG_NO_HZ=y for older kernels).
+1. Never omit scheduling-clock ticks (CONFIG_HZ_PERIODIC=y or
+ CONFIG_NO_HZ=n for older kernels). You normally will -not-
+ want to choose this option.
-2. CPUs having only one runnable task (CONFIG_NO_HZ_FULL=y).
+2. Omit scheduling-clock ticks on idle CPUs (CONFIG_NO_HZ_IDLE=y or
+ CONFIG_NO_HZ=y for older kernels). This is the most common
+ approach, and should be the default.
-These two cases are described in the following two sections, followed
+3. Omit scheduling-clock ticks on CPUs that are either idle or that
+ have only one runnable task (CONFIG_NO_HZ_FULL=y). Unless you
+ are running realtime applications or certain types of HPC
+ workloads, you will normally -not- want this option.
+
+These three cases are described in the following three sections, followed
by a third section on RCU-specific considerations and a fourth and final
section listing known issues.
-IDLE CPUs
+NEVER OMIT SCHEDULING-CLOCK TICKS
+
+Very old versions of Linux from the 1990s and the very early 2000s
+are incapable of omitting scheduling-clock ticks. It turns out that
+there are some situations where this old-school approach is still the
+right approach, for example, in heavy workloads with lots of tasks
+that use short bursts of CPU, where there are very frequent idle
+periods, but where these idle periods are also quite short (tens or
+hundreds of microseconds). For these types of workloads, scheduling
+clock interrupts will normally be delivered any way because there
+will frequently be multiple runnable tasks per CPU. In these cases,
+attempting to turn off the scheduling clock interrupt will have no effect
+other than increasing the overhead of switching to and from idle and
+transitioning between user and kernel execution.
+
+This mode of operation can be selected using CONFIG_HZ_PERIODIC=y (or
+CONFIG_NO_HZ=n for older kernels).
+
+However, if you are instead running a light workload with long idle
+periods, failing to omit scheduling-clock interrupts will result in
+excessive power consumption. This is especially bad on battery-powered
+devices, where it results in extremely short battery lifetimes. If you
+are running light workloads, you should therefore read the following
+section.
+
+In addition, if you are running either a real-time workload or an HPC
+workload with short iterations, the scheduling-clock interrupts can
+degrade your applications performance. If this describes your workload,
+you should read the following two sections.
+
+
+OMIT SCHEDULING-CLOCK TICKS FOR IDLE CPUs
If a CPU is idle, there is little point in sending it a scheduling-clock
interrupt. After all, the primary purpose of a scheduling-clock interrupt
dyntick-idle mode.
-CPUs WITH ONLY ONE RUNNABLE TASK
+OMIT SCHEDULING-CLOCK TICKS FOR CPUs WITH ONLY ONE RUNNABLE TASK
If a CPU has only one runnable task, there is little point in sending it
a scheduling-clock interrupt because there is no other task to switch to.
+Note that omitting scheduling-clock ticks for CPUs with only one runnable
+task implies also omitting them for idle CPUs.
The CONFIG_NO_HZ_FULL=y Kconfig option causes the kernel to avoid
sending scheduling-clock interrupts to CPUs with a single runnable task,
single runnable SCHED_FIFO task and multiple runnable SCHED_OTHER
tasks, even though these interrupts are unnecessary.
+ And even when there are multiple runnable tasks on a given CPU,
+ there is little point in interrupting that CPU until the current
+ running task's timeslice expires, which is almost always way
+ longer than the time of the next scheduling-clock interrupt.
+
Better handling of these sorts of situations is future work.
o A reboot is required to reconfigure both adaptive idle and RCU
scheduling-clock interrupt going in order to support accurate
timekeeping.
-o If there are adaptive-ticks CPUs, there will be at least one
- CPU keeping the scheduling-clock interrupt going, even if all
- CPUs are otherwise idle.
+o If there might potentially be some adaptive-ticks CPUs, there
+ will be at least one CPU keeping the scheduling-clock interrupt
+ going, even if all CPUs are otherwise idle.
+
+ Better handling of this situation is ongoing work.
+
+o Some process-handling operations still require the occasional
+ scheduling-clock tick. These operations include calculating CPU
+ load, maintaining sched average, computing CFS entity vruntime,
+ computing avenrun, and carrying out load balancing. They are
+ currently accommodated by scheduling-clock tick every second
+ or so. On-going work will eliminate the need even for these
+ infrequent scheduling-clock ticks.
up_out:
up_read(¤t->mm->mmap_sem);
- goto out;
+ goto out_srcu;
}
int kvmppc_core_init_vm(struct kvm *kvm)
# define synchronize_irq(irq) barrier()
#endif
-#if defined(CONFIG_TINY_RCU) || defined(CONFIG_TINY_PREEMPT_RCU)
+#if defined(CONFIG_TINY_RCU)
static inline void rcu_nmi_enter(void)
{
#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
/* Internal to kernel */
+extern void rcu_init(void);
extern void rcu_sched_qs(int cpu);
extern void rcu_bh_qs(int cpu);
extern void rcu_check_callbacks(int cpu, int user);
struct task_struct *next) { }
#endif /* CONFIG_RCU_USER_QS */
-extern void exit_rcu(void);
-
/**
* RCU_NONIDLE - Indicate idle-loop code that needs RCU readers
* @a: Code that RCU needs to pay attention to.
#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
#include <linux/rcutree.h>
-#elif defined(CONFIG_TINY_RCU) || defined(CONFIG_TINY_PREEMPT_RCU)
+#elif defined(CONFIG_TINY_RCU)
#include <linux/rcutiny.h>
#else
#error "Unknown RCU implementation specified to kernel configuration"
#include <linux/cache.h>
-static inline void rcu_init(void)
-{
-}
-
static inline void rcu_barrier_bh(void)
{
wait_rcu_gp(call_rcu_bh);
wait_rcu_gp(call_rcu_sched);
}
-#ifdef CONFIG_TINY_RCU
-
static inline void synchronize_rcu_expedited(void)
{
synchronize_sched(); /* Only one CPU, so pretty fast anyway!!! */
rcu_barrier_sched(); /* Only one CPU, so only one list of callbacks! */
}
-#else /* #ifdef CONFIG_TINY_RCU */
-
-void synchronize_rcu_expedited(void);
-
-static inline void rcu_barrier(void)
-{
- wait_rcu_gp(call_rcu);
-}
-
-#endif /* #else #ifdef CONFIG_TINY_RCU */
-
static inline void synchronize_rcu_bh(void)
{
synchronize_sched();
call_rcu(head, func);
}
-#ifdef CONFIG_TINY_RCU
-
-static inline void rcu_preempt_note_context_switch(void)
-{
-}
-
static inline int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
{
*delta_jiffies = ULONG_MAX;
return 0;
}
-#else /* #ifdef CONFIG_TINY_RCU */
-
-void rcu_preempt_note_context_switch(void);
-int rcu_preempt_needs_cpu(void);
-
-static inline int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
-{
- *delta_jiffies = ULONG_MAX;
- return rcu_preempt_needs_cpu();
-}
-
-#endif /* #else #ifdef CONFIG_TINY_RCU */
-
static inline void rcu_note_context_switch(int cpu)
{
rcu_sched_qs(cpu);
- rcu_preempt_note_context_switch();
}
/*
{
}
+static inline void exit_rcu(void)
+{
+}
+
#ifdef CONFIG_DEBUG_LOCK_ALLOC
extern int rcu_scheduler_active __read_mostly;
extern void rcu_scheduler_starting(void);
#ifndef __LINUX_RCUTREE_H
#define __LINUX_RCUTREE_H
-extern void rcu_init(void);
extern void rcu_note_context_switch(int cpu);
extern int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies);
extern void rcu_cpu_stall_reset(void);
extern void rcu_bh_force_quiescent_state(void);
extern void rcu_sched_force_quiescent_state(void);
+extern void exit_rcu(void);
+
extern void rcu_scheduler_starting(void);
extern int rcu_scheduler_active __read_mostly;
__srcu_read_unlock(sp, idx);
}
-/**
- * srcu_read_lock_raw - register a new reader for an SRCU-protected structure.
- * @sp: srcu_struct in which to register the new reader.
- *
- * Enter an SRCU read-side critical section. Similar to srcu_read_lock(),
- * but avoids the RCU-lockdep checking. This means that it is legal to
- * use srcu_read_lock_raw() in one context, for example, in an exception
- * handler, and then have the matching srcu_read_unlock_raw() in another
- * context, for example in the task that took the exception.
- *
- * However, the entire SRCU read-side critical section must reside within a
- * single task. For example, beware of using srcu_read_lock_raw() in
- * a device interrupt handler and srcu_read_unlock() in the interrupted
- * task: This will not work if interrupts are threaded.
- */
-static inline int srcu_read_lock_raw(struct srcu_struct *sp)
-{
- unsigned long flags;
- int ret;
-
- local_irq_save(flags);
- ret = __srcu_read_lock(sp);
- local_irq_restore(flags);
- return ret;
-}
-
-/**
- * srcu_read_unlock_raw - unregister reader from an SRCU-protected structure.
- * @sp: srcu_struct in which to unregister the old reader.
- * @idx: return value from corresponding srcu_read_lock_raw().
- *
- * Exit an SRCU read-side critical section without lockdep-RCU checking.
- * See srcu_read_lock_raw() for more details.
- */
-static inline void srcu_read_unlock_raw(struct srcu_struct *sp, int idx)
-{
- unsigned long flags;
-
- local_irq_save(flags);
- __srcu_read_unlock(sp, idx);
- local_irq_restore(flags);
-}
-
#endif
is not required. This option greatly reduces the
memory footprint of RCU.
-config TINY_PREEMPT_RCU
- bool "Preemptible UP-only small-memory-footprint RCU"
- depends on PREEMPT && !SMP
- help
- This option selects the RCU implementation that is designed
- for real-time UP systems. This option greatly reduces the
- memory footprint of RCU.
-
endchoice
config PREEMPT_RCU
- def_bool ( TREE_PREEMPT_RCU || TINY_PREEMPT_RCU )
+ def_bool TREE_PREEMPT_RCU
help
This option enables preemptible-RCU code that is common between
the TREE_PREEMPT_RCU and TINY_PREEMPT_RCU implementations.
Accept the default if unsure.
config RCU_NOCB_CPU
- bool "Offload RCU callback processing from boot-selected CPUs (EXPERIMENTAL"
+ bool "Offload RCU callback processing from boot-selected CPUs"
depends on TREE_RCU || TREE_PREEMPT_RCU
default n
help
prompt "Build-forced no-CBs CPUs"
default RCU_NOCB_CPU_NONE
help
- This option allows no-CBs CPUs to be specified at build time.
- Additional no-CBs CPUs may be specified by the rcu_nocbs=
- boot parameter.
+ This option allows no-CBs CPUs (whose RCU callbacks are invoked
+ from kthreads rather than from softirq context) to be specified
+ at build time. Additional no-CBs CPUs may be specified by
+ the rcu_nocbs= boot parameter.
config RCU_NOCB_CPU_NONE
bool "No build_forced no-CBs CPUs"
help
This option does not force any of the CPUs to be no-CBs CPUs.
Only CPUs designated by the rcu_nocbs= boot parameter will be
- no-CBs CPUs.
+ no-CBs CPUs, whose RCU callbacks will be invoked by per-CPU
+ kthreads whose names begin with "rcuo". All other CPUs will
+ invoke their own RCU callbacks in softirq context.
+
+ Select this option if you want to choose no-CBs CPUs at
+ boot time, for example, to allow testing of different no-CBs
+ configurations without having to rebuild the kernel each time.
config RCU_NOCB_CPU_ZERO
bool "CPU 0 is a build_forced no-CBs CPU"
depends on RCU_NOCB_CPU && !NO_HZ_FULL
help
- This option forces CPU 0 to be a no-CBs CPU. Additional CPUs
- may be designated as no-CBs CPUs using the rcu_nocbs= boot
- parameter will be no-CBs CPUs.
+ This option forces CPU 0 to be a no-CBs CPU, so that its RCU
+ callbacks are invoked by a per-CPU kthread whose name begins
+ with "rcuo". Additional CPUs may be designated as no-CBs
+ CPUs using the rcu_nocbs= boot parameter will be no-CBs CPUs.
+ All other CPUs will invoke their own RCU callbacks in softirq
+ context.
Select this if CPU 0 needs to be a no-CBs CPU for real-time
- or energy-efficiency reasons.
+ or energy-efficiency reasons, but the real reason it exists
+ is to ensure that randconfig testing covers mixed systems.
config RCU_NOCB_CPU_ALL
bool "All CPUs are build_forced no-CBs CPUs"
depends on RCU_NOCB_CPU
help
This option forces all CPUs to be no-CBs CPUs. The rcu_nocbs=
- boot parameter will be ignored.
+ boot parameter will be ignored. All CPUs' RCU callbacks will
+ be executed in the context of per-CPU rcuo kthreads created for
+ this purpose. Assuming that the kthreads whose names start with
+ "rcuo" are bound to "housekeeping" CPUs, this reduces OS jitter
+ on the remaining CPUs, but might decrease memory locality during
+ RCU-callback invocation, thus potentially degrading throughput.
Select this if all CPUs need to be no-CBs CPUs for real-time
or energy-efficiency reasons.
}
EXPORT_SYMBOL_GPL(__rcu_read_unlock);
-/*
- * Check for a task exiting while in a preemptible-RCU read-side
- * critical section, clean up if so. No need to issue warnings,
- * as debug_check_no_locks_held() already does this if lockdep
- * is enabled.
- */
-void exit_rcu(void)
-{
- struct task_struct *t = current;
-
- if (likely(list_empty(¤t->rcu_node_entry)))
- return;
- t->rcu_read_lock_nesting = 1;
- barrier();
- t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED;
- __rcu_read_unlock();
-}
-
-#else /* #ifdef CONFIG_PREEMPT_RCU */
-
-void exit_rcu(void)
-{
-}
-
-#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
+#endif /* #ifdef CONFIG_PREEMPT_RCU */
#ifdef CONFIG_DEBUG_LOCK_ALLOC
static struct lock_class_key rcu_lock_key;
struct lockdep_map rcu_sched_lock_map =
STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
-#endif
-
-#ifdef CONFIG_DEBUG_LOCK_ALLOC
int debug_lockdep_rcu_enabled(void)
{
/* Forward declarations for rcutiny_plugin.h. */
struct rcu_ctrlblk;
-static void invoke_rcu_callbacks(void);
static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp);
static void rcu_process_callbacks(struct softirq_action *unused);
static void __call_rcu(struct rcu_head *head,
*/
static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
{
- reset_cpu_stall_ticks(rcp);
+ RCU_TRACE(reset_cpu_stall_ticks(rcp));
if (rcp->rcucblist != NULL &&
rcp->donetail != rcp->curtail) {
rcp->donetail = rcp->curtail;
local_irq_save(flags);
if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
rcu_qsctr_help(&rcu_bh_ctrlblk))
- invoke_rcu_callbacks();
+ raise_softirq(RCU_SOFTIRQ);
local_irq_restore(flags);
}
local_irq_save(flags);
if (rcu_qsctr_help(&rcu_bh_ctrlblk))
- invoke_rcu_callbacks();
+ raise_softirq(RCU_SOFTIRQ);
local_irq_restore(flags);
}
*/
void rcu_check_callbacks(int cpu, int user)
{
- check_cpu_stalls();
+ RCU_TRACE(check_cpu_stalls());
if (user || rcu_is_cpu_rrupt_from_idle())
rcu_sched_qs(cpu);
else if (!in_softirq())
rcu_bh_qs(cpu);
- rcu_preempt_check_callbacks();
}
/*
ACCESS_ONCE(rcp->rcucblist),
need_resched(),
is_idle_task(current),
- rcu_is_callbacks_kthread()));
+ false));
return;
}
*rcp->donetail = NULL;
if (rcp->curtail == rcp->donetail)
rcp->curtail = &rcp->rcucblist;
- rcu_preempt_remove_callbacks(rcp);
rcp->donetail = &rcp->rcucblist;
local_irq_restore(flags);
RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));
RCU_TRACE(trace_rcu_batch_end(rcp->name, cb_count, 0, need_resched(),
is_idle_task(current),
- rcu_is_callbacks_kthread()));
+ false));
}
static void rcu_process_callbacks(struct softirq_action *unused)
{
__rcu_process_callbacks(&rcu_sched_ctrlblk);
__rcu_process_callbacks(&rcu_bh_ctrlblk);
- rcu_preempt_process_callbacks();
}
/*
__call_rcu(head, func, &rcu_bh_ctrlblk);
}
EXPORT_SYMBOL_GPL(call_rcu_bh);
+
+void rcu_init(void)
+{
+ open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
+}
};
#ifdef CONFIG_DEBUG_LOCK_ALLOC
+#include <linux/kernel_stat.h>
+
int rcu_scheduler_active __read_mostly;
EXPORT_SYMBOL_GPL(rcu_scheduler_active);
-#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
-
-#ifdef CONFIG_RCU_TRACE
-
-static void check_cpu_stall(struct rcu_ctrlblk *rcp)
-{
- unsigned long j;
- unsigned long js;
-
- if (rcu_cpu_stall_suppress)
- return;
- rcp->ticks_this_gp++;
- j = jiffies;
- js = rcp->jiffies_stall;
- if (*rcp->curtail && ULONG_CMP_GE(j, js)) {
- pr_err("INFO: %s stall on CPU (%lu ticks this GP) idle=%llx (t=%lu jiffies q=%ld)\n",
- rcp->name, rcp->ticks_this_gp, rcu_dynticks_nesting,
- jiffies - rcp->gp_start, rcp->qlen);
- dump_stack();
- }
- if (*rcp->curtail && ULONG_CMP_GE(j, js))
- rcp->jiffies_stall = jiffies +
- 3 * rcu_jiffies_till_stall_check() + 3;
- else if (ULONG_CMP_GE(j, js))
- rcp->jiffies_stall = jiffies + rcu_jiffies_till_stall_check();
-}
-
-static void check_cpu_stall_preempt(void);
-
-#endif /* #ifdef CONFIG_RCU_TRACE */
-
-static void reset_cpu_stall_ticks(struct rcu_ctrlblk *rcp)
-{
-#ifdef CONFIG_RCU_TRACE
- rcp->ticks_this_gp = 0;
- rcp->gp_start = jiffies;
- rcp->jiffies_stall = jiffies + rcu_jiffies_till_stall_check();
-#endif /* #ifdef CONFIG_RCU_TRACE */
-}
-
-static void check_cpu_stalls(void)
-{
- RCU_TRACE(check_cpu_stall(&rcu_bh_ctrlblk));
- RCU_TRACE(check_cpu_stall(&rcu_sched_ctrlblk));
- RCU_TRACE(check_cpu_stall_preempt());
-}
-
-#ifdef CONFIG_TINY_PREEMPT_RCU
-
-#include <linux/delay.h>
-
-/* Global control variables for preemptible RCU. */
-struct rcu_preempt_ctrlblk {
- struct rcu_ctrlblk rcb; /* curtail: ->next ptr of last CB for GP. */
- struct rcu_head **nexttail;
- /* Tasks blocked in a preemptible RCU */
- /* read-side critical section while an */
- /* preemptible-RCU grace period is in */
- /* progress must wait for a later grace */
- /* period. This pointer points to the */
- /* ->next pointer of the last task that */
- /* must wait for a later grace period, or */
- /* to &->rcb.rcucblist if there is no */
- /* such task. */
- struct list_head blkd_tasks;
- /* Tasks blocked in RCU read-side critical */
- /* section. Tasks are placed at the head */
- /* of this list and age towards the tail. */
- struct list_head *gp_tasks;
- /* Pointer to the first task blocking the */
- /* current grace period, or NULL if there */
- /* is no such task. */
- struct list_head *exp_tasks;
- /* Pointer to first task blocking the */
- /* current expedited grace period, or NULL */
- /* if there is no such task. If there */
- /* is no current expedited grace period, */
- /* then there cannot be any such task. */
-#ifdef CONFIG_RCU_BOOST
- struct list_head *boost_tasks;
- /* Pointer to first task that needs to be */
- /* priority-boosted, or NULL if no priority */
- /* boosting is needed. If there is no */
- /* current or expedited grace period, there */
- /* can be no such task. */
-#endif /* #ifdef CONFIG_RCU_BOOST */
- u8 gpnum; /* Current grace period. */
- u8 gpcpu; /* Last grace period blocked by the CPU. */
- u8 completed; /* Last grace period completed. */
- /* If all three are equal, RCU is idle. */
-#ifdef CONFIG_RCU_BOOST
- unsigned long boost_time; /* When to start boosting (jiffies) */
-#endif /* #ifdef CONFIG_RCU_BOOST */
-#ifdef CONFIG_RCU_TRACE
- unsigned long n_grace_periods;
-#ifdef CONFIG_RCU_BOOST
- unsigned long n_tasks_boosted;
- /* Total number of tasks boosted. */
- unsigned long n_exp_boosts;
- /* Number of tasks boosted for expedited GP. */
- unsigned long n_normal_boosts;
- /* Number of tasks boosted for normal GP. */
- unsigned long n_balk_blkd_tasks;
- /* Refused to boost: no blocked tasks. */
- unsigned long n_balk_exp_gp_tasks;
- /* Refused to boost: nothing blocking GP. */
- unsigned long n_balk_boost_tasks;
- /* Refused to boost: already boosting. */
- unsigned long n_balk_notyet;
- /* Refused to boost: not yet time. */
- unsigned long n_balk_nos;
- /* Refused to boost: not sure why, though. */
- /* This can happen due to race conditions. */
-#endif /* #ifdef CONFIG_RCU_BOOST */
-#endif /* #ifdef CONFIG_RCU_TRACE */
-};
-
-static struct rcu_preempt_ctrlblk rcu_preempt_ctrlblk = {
- .rcb.donetail = &rcu_preempt_ctrlblk.rcb.rcucblist,
- .rcb.curtail = &rcu_preempt_ctrlblk.rcb.rcucblist,
- .nexttail = &rcu_preempt_ctrlblk.rcb.rcucblist,
- .blkd_tasks = LIST_HEAD_INIT(rcu_preempt_ctrlblk.blkd_tasks),
- RCU_TRACE(.rcb.name = "rcu_preempt")
-};
-
-static int rcu_preempted_readers_exp(void);
-static void rcu_report_exp_done(void);
-
-/*
- * Return true if the CPU has not yet responded to the current grace period.
- */
-static int rcu_cpu_blocking_cur_gp(void)
-{
- return rcu_preempt_ctrlblk.gpcpu != rcu_preempt_ctrlblk.gpnum;
-}
-
-/*
- * Check for a running RCU reader. Because there is only one CPU,
- * there can be but one running RCU reader at a time. ;-)
- *
- * Returns zero if there are no running readers. Returns a positive
- * number if there is at least one reader within its RCU read-side
- * critical section. Returns a negative number if an outermost reader
- * is in the midst of exiting from its RCU read-side critical section
- *
- * Returns zero if there are no running readers. Returns a positive
- * number if there is at least one reader within its RCU read-side
- * critical section. Returns a negative number if an outermost reader
- * is in the midst of exiting from its RCU read-side critical section.
- */
-static int rcu_preempt_running_reader(void)
-{
- return current->rcu_read_lock_nesting;
-}
-
-/*
- * Check for preempted RCU readers blocking any grace period.
- * If the caller needs a reliable answer, it must disable hard irqs.
- */
-static int rcu_preempt_blocked_readers_any(void)
-{
- return !list_empty(&rcu_preempt_ctrlblk.blkd_tasks);
-}
-
-/*
- * Check for preempted RCU readers blocking the current grace period.
- * If the caller needs a reliable answer, it must disable hard irqs.
- */
-static int rcu_preempt_blocked_readers_cgp(void)
-{
- return rcu_preempt_ctrlblk.gp_tasks != NULL;
-}
-
-/*
- * Return true if another preemptible-RCU grace period is needed.
- */
-static int rcu_preempt_needs_another_gp(void)
-{
- return *rcu_preempt_ctrlblk.rcb.curtail != NULL;
-}
-
-/*
- * Return true if a preemptible-RCU grace period is in progress.
- * The caller must disable hardirqs.
- */
-static int rcu_preempt_gp_in_progress(void)
-{
- return rcu_preempt_ctrlblk.completed != rcu_preempt_ctrlblk.gpnum;
-}
-
-/*
- * Advance a ->blkd_tasks-list pointer to the next entry, instead
- * returning NULL if at the end of the list.
- */
-static struct list_head *rcu_next_node_entry(struct task_struct *t)
-{
- struct list_head *np;
-
- np = t->rcu_node_entry.next;
- if (np == &rcu_preempt_ctrlblk.blkd_tasks)
- np = NULL;
- return np;
-}
-
-#ifdef CONFIG_RCU_TRACE
-
-#ifdef CONFIG_RCU_BOOST
-static void rcu_initiate_boost_trace(void);
-#endif /* #ifdef CONFIG_RCU_BOOST */
-
-/*
- * Dump additional statistice for TINY_PREEMPT_RCU.
- */
-static void show_tiny_preempt_stats(struct seq_file *m)
-{
- seq_printf(m, "rcu_preempt: qlen=%ld gp=%lu g%u/p%u/c%u tasks=%c%c%c\n",
- rcu_preempt_ctrlblk.rcb.qlen,
- rcu_preempt_ctrlblk.n_grace_periods,
- rcu_preempt_ctrlblk.gpnum,
- rcu_preempt_ctrlblk.gpcpu,
- rcu_preempt_ctrlblk.completed,
- "T."[list_empty(&rcu_preempt_ctrlblk.blkd_tasks)],
- "N."[!rcu_preempt_ctrlblk.gp_tasks],
- "E."[!rcu_preempt_ctrlblk.exp_tasks]);
-#ifdef CONFIG_RCU_BOOST
- seq_printf(m, "%sttb=%c ntb=%lu neb=%lu nnb=%lu j=%04x bt=%04x\n",
- " ",
- "B."[!rcu_preempt_ctrlblk.boost_tasks],
- rcu_preempt_ctrlblk.n_tasks_boosted,
- rcu_preempt_ctrlblk.n_exp_boosts,
- rcu_preempt_ctrlblk.n_normal_boosts,
- (int)(jiffies & 0xffff),
- (int)(rcu_preempt_ctrlblk.boost_time & 0xffff));
- seq_printf(m, "%s: nt=%lu egt=%lu bt=%lu ny=%lu nos=%lu\n",
- " balk",
- rcu_preempt_ctrlblk.n_balk_blkd_tasks,
- rcu_preempt_ctrlblk.n_balk_exp_gp_tasks,
- rcu_preempt_ctrlblk.n_balk_boost_tasks,
- rcu_preempt_ctrlblk.n_balk_notyet,
- rcu_preempt_ctrlblk.n_balk_nos);
-#endif /* #ifdef CONFIG_RCU_BOOST */
-}
-
-#endif /* #ifdef CONFIG_RCU_TRACE */
-
-#ifdef CONFIG_RCU_BOOST
-
-#include "rtmutex_common.h"
-
-#define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
-
-/* Controls for rcu_kthread() kthread. */
-static struct task_struct *rcu_kthread_task;
-static DECLARE_WAIT_QUEUE_HEAD(rcu_kthread_wq);
-static unsigned long have_rcu_kthread_work;
-
-/*
- * Carry out RCU priority boosting on the task indicated by ->boost_tasks,
- * and advance ->boost_tasks to the next task in the ->blkd_tasks list.
- */
-static int rcu_boost(void)
-{
- unsigned long flags;
- struct rt_mutex mtx;
- struct task_struct *t;
- struct list_head *tb;
-
- if (rcu_preempt_ctrlblk.boost_tasks == NULL &&
- rcu_preempt_ctrlblk.exp_tasks == NULL)
- return 0; /* Nothing to boost. */
-
- local_irq_save(flags);
-
- /*
- * Recheck with irqs disabled: all tasks in need of boosting
- * might exit their RCU read-side critical sections on their own
- * if we are preempted just before disabling irqs.
- */
- if (rcu_preempt_ctrlblk.boost_tasks == NULL &&
- rcu_preempt_ctrlblk.exp_tasks == NULL) {
- local_irq_restore(flags);
- return 0;
- }
-
- /*
- * Preferentially boost tasks blocking expedited grace periods.
- * This cannot starve the normal grace periods because a second
- * expedited grace period must boost all blocked tasks, including
- * those blocking the pre-existing normal grace period.
- */
- if (rcu_preempt_ctrlblk.exp_tasks != NULL) {
- tb = rcu_preempt_ctrlblk.exp_tasks;
- RCU_TRACE(rcu_preempt_ctrlblk.n_exp_boosts++);
- } else {
- tb = rcu_preempt_ctrlblk.boost_tasks;
- RCU_TRACE(rcu_preempt_ctrlblk.n_normal_boosts++);
- }
- RCU_TRACE(rcu_preempt_ctrlblk.n_tasks_boosted++);
-
- /*
- * We boost task t by manufacturing an rt_mutex that appears to
- * be held by task t. We leave a pointer to that rt_mutex where
- * task t can find it, and task t will release the mutex when it
- * exits its outermost RCU read-side critical section. Then
- * simply acquiring this artificial rt_mutex will boost task
- * t's priority. (Thanks to tglx for suggesting this approach!)
- */
- t = container_of(tb, struct task_struct, rcu_node_entry);
- rt_mutex_init_proxy_locked(&mtx, t);
- t->rcu_boost_mutex = &mtx;
- local_irq_restore(flags);
- rt_mutex_lock(&mtx);
- rt_mutex_unlock(&mtx); /* Keep lockdep happy. */
-
- return ACCESS_ONCE(rcu_preempt_ctrlblk.boost_tasks) != NULL ||
- ACCESS_ONCE(rcu_preempt_ctrlblk.exp_tasks) != NULL;
-}
-
-/*
- * Check to see if it is now time to start boosting RCU readers blocking
- * the current grace period, and, if so, tell the rcu_kthread_task to
- * start boosting them. If there is an expedited boost in progress,
- * we wait for it to complete.
- *
- * If there are no blocked readers blocking the current grace period,
- * return 0 to let the caller know, otherwise return 1. Note that this
- * return value is independent of whether or not boosting was done.
- */
-static int rcu_initiate_boost(void)
-{
- if (!rcu_preempt_blocked_readers_cgp() &&
- rcu_preempt_ctrlblk.exp_tasks == NULL) {
- RCU_TRACE(rcu_preempt_ctrlblk.n_balk_exp_gp_tasks++);
- return 0;
- }
- if (rcu_preempt_ctrlblk.exp_tasks != NULL ||
- (rcu_preempt_ctrlblk.gp_tasks != NULL &&
- rcu_preempt_ctrlblk.boost_tasks == NULL &&
- ULONG_CMP_GE(jiffies, rcu_preempt_ctrlblk.boost_time))) {
- if (rcu_preempt_ctrlblk.exp_tasks == NULL)
- rcu_preempt_ctrlblk.boost_tasks =
- rcu_preempt_ctrlblk.gp_tasks;
- invoke_rcu_callbacks();
- } else {
- RCU_TRACE(rcu_initiate_boost_trace());
- }
- return 1;
-}
-
-#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
-
-/*
- * Do priority-boost accounting for the start of a new grace period.
- */
-static void rcu_preempt_boost_start_gp(void)
-{
- rcu_preempt_ctrlblk.boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
-}
-
-#else /* #ifdef CONFIG_RCU_BOOST */
-
-/*
- * If there is no RCU priority boosting, we don't initiate boosting,
- * but we do indicate whether there are blocked readers blocking the
- * current grace period.
- */
-static int rcu_initiate_boost(void)
-{
- return rcu_preempt_blocked_readers_cgp();
-}
-
-/*
- * If there is no RCU priority boosting, nothing to do at grace-period start.
- */
-static void rcu_preempt_boost_start_gp(void)
-{
-}
-
-#endif /* else #ifdef CONFIG_RCU_BOOST */
-
-/*
- * Record a preemptible-RCU quiescent state for the specified CPU. Note
- * that this just means that the task currently running on the CPU is
- * in a quiescent state. There might be any number of tasks blocked
- * while in an RCU read-side critical section.
- *
- * Unlike the other rcu_*_qs() functions, callers to this function
- * must disable irqs in order to protect the assignment to
- * ->rcu_read_unlock_special.
- *
- * Because this is a single-CPU implementation, the only way a grace
- * period can end is if the CPU is in a quiescent state. The reason is
- * that a blocked preemptible-RCU reader can exit its critical section
- * only if the CPU is running it at the time. Therefore, when the
- * last task blocking the current grace period exits its RCU read-side
- * critical section, neither the CPU nor blocked tasks will be stopping
- * the current grace period. (In contrast, SMP implementations
- * might have CPUs running in RCU read-side critical sections that
- * block later grace periods -- but this is not possible given only
- * one CPU.)
- */
-static void rcu_preempt_cpu_qs(void)
-{
- /* Record both CPU and task as having responded to current GP. */
- rcu_preempt_ctrlblk.gpcpu = rcu_preempt_ctrlblk.gpnum;
- current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
-
- /* If there is no GP then there is nothing more to do. */
- if (!rcu_preempt_gp_in_progress())
- return;
- /*
- * Check up on boosting. If there are readers blocking the
- * current grace period, leave.
- */
- if (rcu_initiate_boost())
- return;
-
- /* Advance callbacks. */
- rcu_preempt_ctrlblk.completed = rcu_preempt_ctrlblk.gpnum;
- rcu_preempt_ctrlblk.rcb.donetail = rcu_preempt_ctrlblk.rcb.curtail;
- rcu_preempt_ctrlblk.rcb.curtail = rcu_preempt_ctrlblk.nexttail;
-
- /* If there are no blocked readers, next GP is done instantly. */
- if (!rcu_preempt_blocked_readers_any())
- rcu_preempt_ctrlblk.rcb.donetail = rcu_preempt_ctrlblk.nexttail;
-
- /* If there are done callbacks, cause them to be invoked. */
- if (*rcu_preempt_ctrlblk.rcb.donetail != NULL)
- invoke_rcu_callbacks();
-}
-
-/*
- * Start a new RCU grace period if warranted. Hard irqs must be disabled.
- */
-static void rcu_preempt_start_gp(void)
-{
- if (!rcu_preempt_gp_in_progress() && rcu_preempt_needs_another_gp()) {
-
- /* Official start of GP. */
- rcu_preempt_ctrlblk.gpnum++;
- RCU_TRACE(rcu_preempt_ctrlblk.n_grace_periods++);
- reset_cpu_stall_ticks(&rcu_preempt_ctrlblk.rcb);
-
- /* Any blocked RCU readers block new GP. */
- if (rcu_preempt_blocked_readers_any())
- rcu_preempt_ctrlblk.gp_tasks =
- rcu_preempt_ctrlblk.blkd_tasks.next;
-
- /* Set up for RCU priority boosting. */
- rcu_preempt_boost_start_gp();
-
- /* If there is no running reader, CPU is done with GP. */
- if (!rcu_preempt_running_reader())
- rcu_preempt_cpu_qs();
- }
-}
-
-/*
- * We have entered the scheduler, and the current task might soon be
- * context-switched away from. If this task is in an RCU read-side
- * critical section, we will no longer be able to rely on the CPU to
- * record that fact, so we enqueue the task on the blkd_tasks list.
- * If the task started after the current grace period began, as recorded
- * by ->gpcpu, we enqueue at the beginning of the list. Otherwise
- * before the element referenced by ->gp_tasks (or at the tail if
- * ->gp_tasks is NULL) and point ->gp_tasks at the newly added element.
- * The task will dequeue itself when it exits the outermost enclosing
- * RCU read-side critical section. Therefore, the current grace period
- * cannot be permitted to complete until the ->gp_tasks pointer becomes
- * NULL.
- *
- * Caller must disable preemption.
- */
-void rcu_preempt_note_context_switch(void)
-{
- struct task_struct *t = current;
- unsigned long flags;
-
- local_irq_save(flags); /* must exclude scheduler_tick(). */
- if (rcu_preempt_running_reader() > 0 &&
- (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
-
- /* Possibly blocking in an RCU read-side critical section. */
- t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
-
- /*
- * If this CPU has already checked in, then this task
- * will hold up the next grace period rather than the
- * current grace period. Queue the task accordingly.
- * If the task is queued for the current grace period
- * (i.e., this CPU has not yet passed through a quiescent
- * state for the current grace period), then as long
- * as that task remains queued, the current grace period
- * cannot end.
- */
- list_add(&t->rcu_node_entry, &rcu_preempt_ctrlblk.blkd_tasks);
- if (rcu_cpu_blocking_cur_gp())
- rcu_preempt_ctrlblk.gp_tasks = &t->rcu_node_entry;
- } else if (rcu_preempt_running_reader() < 0 &&
- t->rcu_read_unlock_special) {
- /*
- * Complete exit from RCU read-side critical section on
- * behalf of preempted instance of __rcu_read_unlock().
- */
- rcu_read_unlock_special(t);
- }
-
- /*
- * Either we were not in an RCU read-side critical section to
- * begin with, or we have now recorded that critical section
- * globally. Either way, we can now note a quiescent state
- * for this CPU. Again, if we were in an RCU read-side critical
- * section, and if that critical section was blocking the current
- * grace period, then the fact that the task has been enqueued
- * means that current grace period continues to be blocked.
- */
- rcu_preempt_cpu_qs();
- local_irq_restore(flags);
-}
-
-/*
- * Handle special cases during rcu_read_unlock(), such as needing to
- * notify RCU core processing or task having blocked during the RCU
- * read-side critical section.
- */
-void rcu_read_unlock_special(struct task_struct *t)
-{
- int empty;
- int empty_exp;
- unsigned long flags;
- struct list_head *np;
-#ifdef CONFIG_RCU_BOOST
- struct rt_mutex *rbmp = NULL;
-#endif /* #ifdef CONFIG_RCU_BOOST */
- int special;
-
- /*
- * NMI handlers cannot block and cannot safely manipulate state.
- * They therefore cannot possibly be special, so just leave.
- */
- if (in_nmi())
- return;
-
- local_irq_save(flags);
-
- /*
- * If RCU core is waiting for this CPU to exit critical section,
- * let it know that we have done so.
- */
- special = t->rcu_read_unlock_special;
- if (special & RCU_READ_UNLOCK_NEED_QS)
- rcu_preempt_cpu_qs();
-
- /* Hardware IRQ handlers cannot block. */
- if (in_irq() || in_serving_softirq()) {
- local_irq_restore(flags);
- return;
- }
-
- /* Clean up if blocked during RCU read-side critical section. */
- if (special & RCU_READ_UNLOCK_BLOCKED) {
- t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;
-
- /*
- * Remove this task from the ->blkd_tasks list and adjust
- * any pointers that might have been referencing it.
- */
- empty = !rcu_preempt_blocked_readers_cgp();
- empty_exp = rcu_preempt_ctrlblk.exp_tasks == NULL;
- np = rcu_next_node_entry(t);
- list_del_init(&t->rcu_node_entry);
- if (&t->rcu_node_entry == rcu_preempt_ctrlblk.gp_tasks)
- rcu_preempt_ctrlblk.gp_tasks = np;
- if (&t->rcu_node_entry == rcu_preempt_ctrlblk.exp_tasks)
- rcu_preempt_ctrlblk.exp_tasks = np;
-#ifdef CONFIG_RCU_BOOST
- if (&t->rcu_node_entry == rcu_preempt_ctrlblk.boost_tasks)
- rcu_preempt_ctrlblk.boost_tasks = np;
-#endif /* #ifdef CONFIG_RCU_BOOST */
-
- /*
- * If this was the last task on the current list, and if
- * we aren't waiting on the CPU, report the quiescent state
- * and start a new grace period if needed.
- */
- if (!empty && !rcu_preempt_blocked_readers_cgp()) {
- rcu_preempt_cpu_qs();
- rcu_preempt_start_gp();
- }
-
- /*
- * If this was the last task on the expedited lists,
- * then we need wake up the waiting task.
- */
- if (!empty_exp && rcu_preempt_ctrlblk.exp_tasks == NULL)
- rcu_report_exp_done();
- }
-#ifdef CONFIG_RCU_BOOST
- /* Unboost self if was boosted. */
- if (t->rcu_boost_mutex != NULL) {
- rbmp = t->rcu_boost_mutex;
- t->rcu_boost_mutex = NULL;
- rt_mutex_unlock(rbmp);
- }
-#endif /* #ifdef CONFIG_RCU_BOOST */
- local_irq_restore(flags);
-}
-
-/*
- * Check for a quiescent state from the current CPU. When a task blocks,
- * the task is recorded in the rcu_preempt_ctrlblk structure, which is
- * checked elsewhere. This is called from the scheduling-clock interrupt.
- *
- * Caller must disable hard irqs.
- */
-static void rcu_preempt_check_callbacks(void)
-{
- struct task_struct *t = current;
-
- if (rcu_preempt_gp_in_progress() &&
- (!rcu_preempt_running_reader() ||
- !rcu_cpu_blocking_cur_gp()))
- rcu_preempt_cpu_qs();
- if (&rcu_preempt_ctrlblk.rcb.rcucblist !=
- rcu_preempt_ctrlblk.rcb.donetail)
- invoke_rcu_callbacks();
- if (rcu_preempt_gp_in_progress() &&
- rcu_cpu_blocking_cur_gp() &&
- rcu_preempt_running_reader() > 0)
- t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
-}
-
-/*
- * TINY_PREEMPT_RCU has an extra callback-list tail pointer to
- * update, so this is invoked from rcu_process_callbacks() to
- * handle that case. Of course, it is invoked for all flavors of
- * RCU, but RCU callbacks can appear only on one of the lists, and
- * neither ->nexttail nor ->donetail can possibly be NULL, so there
- * is no need for an explicit check.
- */
-static void rcu_preempt_remove_callbacks(struct rcu_ctrlblk *rcp)
-{
- if (rcu_preempt_ctrlblk.nexttail == rcp->donetail)
- rcu_preempt_ctrlblk.nexttail = &rcp->rcucblist;
-}
-
-/*
- * Process callbacks for preemptible RCU.
- */
-static void rcu_preempt_process_callbacks(void)
-{
- __rcu_process_callbacks(&rcu_preempt_ctrlblk.rcb);
-}
-
-/*
- * Queue a preemptible -RCU callback for invocation after a grace period.
- */
-void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
-{
- unsigned long flags;
-
- debug_rcu_head_queue(head);
- head->func = func;
- head->next = NULL;
-
- local_irq_save(flags);
- *rcu_preempt_ctrlblk.nexttail = head;
- rcu_preempt_ctrlblk.nexttail = &head->next;
- RCU_TRACE(rcu_preempt_ctrlblk.rcb.qlen++);
- rcu_preempt_start_gp(); /* checks to see if GP needed. */
- local_irq_restore(flags);
-}
-EXPORT_SYMBOL_GPL(call_rcu);
-
-/*
- * synchronize_rcu - wait until a grace period has elapsed.
- *
- * Control will return to the caller some time after a full grace
- * period has elapsed, in other words after all currently executing RCU
- * read-side critical sections have completed. RCU read-side critical
- * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
- * and may be nested.
- */
-void synchronize_rcu(void)
-{
- rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
- !lock_is_held(&rcu_lock_map) &&
- !lock_is_held(&rcu_sched_lock_map),
- "Illegal synchronize_rcu() in RCU read-side critical section");
-
-#ifdef CONFIG_DEBUG_LOCK_ALLOC
- if (!rcu_scheduler_active)
- return;
-#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
-
- WARN_ON_ONCE(rcu_preempt_running_reader());
- if (!rcu_preempt_blocked_readers_any())
- return;
-
- /* Once we get past the fastpath checks, same code as rcu_barrier(). */
- if (rcu_expedited)
- synchronize_rcu_expedited();
- else
- rcu_barrier();
-}
-EXPORT_SYMBOL_GPL(synchronize_rcu);
-
-static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
-static unsigned long sync_rcu_preempt_exp_count;
-static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);
-
-/*
- * Return non-zero if there are any tasks in RCU read-side critical
- * sections blocking the current preemptible-RCU expedited grace period.
- * If there is no preemptible-RCU expedited grace period currently in
- * progress, returns zero unconditionally.
- */
-static int rcu_preempted_readers_exp(void)
-{
- return rcu_preempt_ctrlblk.exp_tasks != NULL;
-}
-
-/*
- * Report the exit from RCU read-side critical section for the last task
- * that queued itself during or before the current expedited preemptible-RCU
- * grace period.
- */
-static void rcu_report_exp_done(void)
-{
- wake_up(&sync_rcu_preempt_exp_wq);
-}
-
-/*
- * Wait for an rcu-preempt grace period, but expedite it. The basic idea
- * is to rely in the fact that there is but one CPU, and that it is
- * illegal for a task to invoke synchronize_rcu_expedited() while in a
- * preemptible-RCU read-side critical section. Therefore, any such
- * critical sections must correspond to blocked tasks, which must therefore
- * be on the ->blkd_tasks list. So just record the current head of the
- * list in the ->exp_tasks pointer, and wait for all tasks including and
- * after the task pointed to by ->exp_tasks to drain.
- */
-void synchronize_rcu_expedited(void)
-{
- unsigned long flags;
- struct rcu_preempt_ctrlblk *rpcp = &rcu_preempt_ctrlblk;
- unsigned long snap;
-
- barrier(); /* ensure prior action seen before grace period. */
-
- WARN_ON_ONCE(rcu_preempt_running_reader());
-
- /*
- * Acquire lock so that there is only one preemptible RCU grace
- * period in flight. Of course, if someone does the expedited
- * grace period for us while we are acquiring the lock, just leave.
- */
- snap = sync_rcu_preempt_exp_count + 1;
- mutex_lock(&sync_rcu_preempt_exp_mutex);
- if (ULONG_CMP_LT(snap, sync_rcu_preempt_exp_count))
- goto unlock_mb_ret; /* Others did our work for us. */
-
- local_irq_save(flags);
-
- /*
- * All RCU readers have to already be on blkd_tasks because
- * we cannot legally be executing in an RCU read-side critical
- * section.
- */
-
- /* Snapshot current head of ->blkd_tasks list. */
- rpcp->exp_tasks = rpcp->blkd_tasks.next;
- if (rpcp->exp_tasks == &rpcp->blkd_tasks)
- rpcp->exp_tasks = NULL;
-
- /* Wait for tail of ->blkd_tasks list to drain. */
- if (!rcu_preempted_readers_exp()) {
- local_irq_restore(flags);
- } else {
- rcu_initiate_boost();
- local_irq_restore(flags);
- wait_event(sync_rcu_preempt_exp_wq,
- !rcu_preempted_readers_exp());
- }
-
- /* Clean up and exit. */
- barrier(); /* ensure expedited GP seen before counter increment. */
- sync_rcu_preempt_exp_count++;
-unlock_mb_ret:
- mutex_unlock(&sync_rcu_preempt_exp_mutex);
- barrier(); /* ensure subsequent action seen after grace period. */
-}
-EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
-
-/*
- * Does preemptible RCU need the CPU to stay out of dynticks mode?
- */
-int rcu_preempt_needs_cpu(void)
-{
- return rcu_preempt_ctrlblk.rcb.rcucblist != NULL;
-}
-
-#else /* #ifdef CONFIG_TINY_PREEMPT_RCU */
-
-#ifdef CONFIG_RCU_TRACE
-
-/*
- * Because preemptible RCU does not exist, it is not necessary to
- * dump out its statistics.
- */
-static void show_tiny_preempt_stats(struct seq_file *m)
-{
-}
-
-#endif /* #ifdef CONFIG_RCU_TRACE */
-
-/*
- * Because preemptible RCU does not exist, it never has any callbacks
- * to check.
- */
-static void rcu_preempt_check_callbacks(void)
-{
-}
-
-/*
- * Because preemptible RCU does not exist, it never has any callbacks
- * to remove.
- */
-static void rcu_preempt_remove_callbacks(struct rcu_ctrlblk *rcp)
-{
-}
-
-/*
- * Because preemptible RCU does not exist, it never has any callbacks
- * to process.
- */
-static void rcu_preempt_process_callbacks(void)
-{
-}
-
-#endif /* #else #ifdef CONFIG_TINY_PREEMPT_RCU */
-
-#ifdef CONFIG_RCU_BOOST
-
-/*
- * Wake up rcu_kthread() to process callbacks now eligible for invocation
- * or to boost readers.
- */
-static void invoke_rcu_callbacks(void)
-{
- have_rcu_kthread_work = 1;
- if (rcu_kthread_task != NULL)
- wake_up(&rcu_kthread_wq);
-}
-
-#ifdef CONFIG_RCU_TRACE
-
-/*
- * Is the current CPU running the RCU-callbacks kthread?
- * Caller must have preemption disabled.
- */
-static bool rcu_is_callbacks_kthread(void)
-{
- return rcu_kthread_task == current;
-}
-
-#endif /* #ifdef CONFIG_RCU_TRACE */
-
-/*
- * This kthread invokes RCU callbacks whose grace periods have
- * elapsed. It is awakened as needed, and takes the place of the
- * RCU_SOFTIRQ that is used for this purpose when boosting is disabled.
- * This is a kthread, but it is never stopped, at least not until
- * the system goes down.
- */
-static int rcu_kthread(void *arg)
-{
- unsigned long work;
- unsigned long morework;
- unsigned long flags;
-
- for (;;) {
- wait_event_interruptible(rcu_kthread_wq,
- have_rcu_kthread_work != 0);
- morework = rcu_boost();
- local_irq_save(flags);
- work = have_rcu_kthread_work;
- have_rcu_kthread_work = morework;
- local_irq_restore(flags);
- if (work)
- rcu_process_callbacks(NULL);
- schedule_timeout_interruptible(1); /* Leave CPU for others. */
- }
-
- return 0; /* Not reached, but needed to shut gcc up. */
-}
-
-/*
- * Spawn the kthread that invokes RCU callbacks.
- */
-static int __init rcu_spawn_kthreads(void)
-{
- struct sched_param sp;
-
- rcu_kthread_task = kthread_run(rcu_kthread, NULL, "rcu_kthread");
- sp.sched_priority = RCU_BOOST_PRIO;
- sched_setscheduler_nocheck(rcu_kthread_task, SCHED_FIFO, &sp);
- return 0;
-}
-early_initcall(rcu_spawn_kthreads);
-
-#else /* #ifdef CONFIG_RCU_BOOST */
-
-/* Hold off callback invocation until early_initcall() time. */
-static int rcu_scheduler_fully_active __read_mostly;
-
-/*
- * Start up softirq processing of callbacks.
- */
-void invoke_rcu_callbacks(void)
-{
- if (rcu_scheduler_fully_active)
- raise_softirq(RCU_SOFTIRQ);
-}
-
-#ifdef CONFIG_RCU_TRACE
-
-/*
- * There is no callback kthread, so this thread is never it.
- */
-static bool rcu_is_callbacks_kthread(void)
-{
- return false;
-}
-
-#endif /* #ifdef CONFIG_RCU_TRACE */
-
-static int __init rcu_scheduler_really_started(void)
-{
- rcu_scheduler_fully_active = 1;
- open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
- raise_softirq(RCU_SOFTIRQ); /* Invoke any callbacks from early boot. */
- return 0;
-}
-early_initcall(rcu_scheduler_really_started);
-
-#endif /* #else #ifdef CONFIG_RCU_BOOST */
-
-#ifdef CONFIG_DEBUG_LOCK_ALLOC
-#include <linux/kernel_stat.h>
/*
* During boot, we forgive RCU lockdep issues. After this function is
#ifdef CONFIG_RCU_TRACE
-#ifdef CONFIG_RCU_BOOST
-
-static void rcu_initiate_boost_trace(void)
-{
- if (list_empty(&rcu_preempt_ctrlblk.blkd_tasks))
- rcu_preempt_ctrlblk.n_balk_blkd_tasks++;
- else if (rcu_preempt_ctrlblk.gp_tasks == NULL &&
- rcu_preempt_ctrlblk.exp_tasks == NULL)
- rcu_preempt_ctrlblk.n_balk_exp_gp_tasks++;
- else if (rcu_preempt_ctrlblk.boost_tasks != NULL)
- rcu_preempt_ctrlblk.n_balk_boost_tasks++;
- else if (!ULONG_CMP_GE(jiffies, rcu_preempt_ctrlblk.boost_time))
- rcu_preempt_ctrlblk.n_balk_notyet++;
- else
- rcu_preempt_ctrlblk.n_balk_nos++;
-}
-
-#endif /* #ifdef CONFIG_RCU_BOOST */
-
static void rcu_trace_sub_qlen(struct rcu_ctrlblk *rcp, int n)
{
unsigned long flags;
*/
static int show_tiny_stats(struct seq_file *m, void *unused)
{
- show_tiny_preempt_stats(m);
seq_printf(m, "rcu_sched: qlen: %ld\n", rcu_sched_ctrlblk.qlen);
seq_printf(m, "rcu_bh: qlen: %ld\n", rcu_bh_ctrlblk.qlen);
return 0;
MODULE_DESCRIPTION("Read-Copy Update tracing for tiny implementation");
MODULE_LICENSE("GPL");
-static void check_cpu_stall_preempt(void)
+static void check_cpu_stall(struct rcu_ctrlblk *rcp)
{
-#ifdef CONFIG_TINY_PREEMPT_RCU
- check_cpu_stall(&rcu_preempt_ctrlblk.rcb);
-#endif /* #ifdef CONFIG_TINY_PREEMPT_RCU */
+ unsigned long j;
+ unsigned long js;
+
+ if (rcu_cpu_stall_suppress)
+ return;
+ rcp->ticks_this_gp++;
+ j = jiffies;
+ js = rcp->jiffies_stall;
+ if (*rcp->curtail && ULONG_CMP_GE(j, js)) {
+ pr_err("INFO: %s stall on CPU (%lu ticks this GP) idle=%llx (t=%lu jiffies q=%ld)\n",
+ rcp->name, rcp->ticks_this_gp, rcu_dynticks_nesting,
+ jiffies - rcp->gp_start, rcp->qlen);
+ dump_stack();
+ }
+ if (*rcp->curtail && ULONG_CMP_GE(j, js))
+ rcp->jiffies_stall = jiffies +
+ 3 * rcu_jiffies_till_stall_check() + 3;
+ else if (ULONG_CMP_GE(j, js))
+ rcp->jiffies_stall = jiffies + rcu_jiffies_till_stall_check();
+}
+
+static void reset_cpu_stall_ticks(struct rcu_ctrlblk *rcp)
+{
+ rcp->ticks_this_gp = 0;
+ rcp->gp_start = jiffies;
+ rcp->jiffies_stall = jiffies + rcu_jiffies_till_stall_check();
+}
+
+static void check_cpu_stalls(void)
+{
+ RCU_TRACE(check_cpu_stall(&rcu_bh_ctrlblk));
+ RCU_TRACE(check_cpu_stall(&rcu_sched_ctrlblk));
}
#endif /* #ifdef CONFIG_RCU_TRACE */
.name = "srcu_sync"
};
-static int srcu_torture_read_lock_raw(void) __acquires(&srcu_ctl)
-{
- return srcu_read_lock_raw(&srcu_ctl);
-}
-
-static void srcu_torture_read_unlock_raw(int idx) __releases(&srcu_ctl)
-{
- srcu_read_unlock_raw(&srcu_ctl, idx);
-}
-
-static struct rcu_torture_ops srcu_raw_ops = {
- .init = rcu_sync_torture_init,
- .readlock = srcu_torture_read_lock_raw,
- .read_delay = srcu_read_delay,
- .readunlock = srcu_torture_read_unlock_raw,
- .completed = srcu_torture_completed,
- .deferred_free = srcu_torture_deferred_free,
- .sync = srcu_torture_synchronize,
- .call = NULL,
- .cb_barrier = NULL,
- .stats = srcu_torture_stats,
- .name = "srcu_raw"
-};
-
-static struct rcu_torture_ops srcu_raw_sync_ops = {
- .init = rcu_sync_torture_init,
- .readlock = srcu_torture_read_lock_raw,
- .read_delay = srcu_read_delay,
- .readunlock = srcu_torture_read_unlock_raw,
- .completed = srcu_torture_completed,
- .deferred_free = rcu_sync_torture_deferred_free,
- .sync = srcu_torture_synchronize,
- .call = NULL,
- .cb_barrier = NULL,
- .stats = srcu_torture_stats,
- .name = "srcu_raw_sync"
-};
-
static void srcu_torture_synchronize_expedited(void)
{
synchronize_srcu_expedited(&srcu_ctl);
{ &rcu_ops, &rcu_sync_ops, &rcu_expedited_ops,
&rcu_bh_ops, &rcu_bh_sync_ops, &rcu_bh_expedited_ops,
&srcu_ops, &srcu_sync_ops, &srcu_expedited_ops,
- &srcu_raw_ops, &srcu_raw_sync_ops,
&sched_ops, &sched_sync_ops, &sched_expedited_ops, };
mutex_lock(&fullstop_mutex);
module_param(qhimark, long, 0444);
module_param(qlowmark, long, 0444);
-static ulong jiffies_till_first_fqs = RCU_JIFFIES_TILL_FORCE_QS;
-static ulong jiffies_till_next_fqs = RCU_JIFFIES_TILL_FORCE_QS;
+static ulong jiffies_till_first_fqs = ULONG_MAX;
+static ulong jiffies_till_next_fqs = ULONG_MAX;
module_param(jiffies_till_first_fqs, ulong, 0644);
module_param(jiffies_till_next_fqs, ulong, 0644);
* See Documentation/RCU/stallwarn.txt for info on how to debug
* RCU CPU stall warnings.
*/
- printk(KERN_ERR "INFO: %s detected stalls on CPUs/tasks:",
+ pr_err("INFO: %s detected stalls on CPUs/tasks:",
rsp->name);
print_cpu_stall_info_begin();
rcu_for_each_leaf_node(rsp, rnp) {
smp_processor_id(), (long)(jiffies - rsp->gp_start),
rsp->gpnum, rsp->completed, totqlen);
if (ndetected == 0)
- printk(KERN_ERR "INFO: Stall ended before state dump start\n");
+ pr_err("INFO: Stall ended before state dump start\n");
else if (!trigger_all_cpu_backtrace())
rcu_dump_cpu_stacks(rsp);
* See Documentation/RCU/stallwarn.txt for info on how to debug
* RCU CPU stall warnings.
*/
- printk(KERN_ERR "INFO: %s self-detected stall on CPU", rsp->name);
+ pr_err("INFO: %s self-detected stall on CPU", rsp->name);
print_cpu_stall_info_begin();
print_cpu_stall_info(rsp, smp_processor_id());
print_cpu_stall_info_end();
rsp->jiffies_stall = jiffies + ULONG_MAX / 2;
}
-/*
- * Update CPU-local rcu_data state to record the newly noticed grace period.
- * This is used both when we started the grace period and when we notice
- * that someone else started the grace period. The caller must hold the
- * ->lock of the leaf rcu_node structure corresponding to the current CPU,
- * and must have irqs disabled.
- */
-static void __note_new_gpnum(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp)
-{
- if (rdp->gpnum != rnp->gpnum) {
- /*
- * If the current grace period is waiting for this CPU,
- * set up to detect a quiescent state, otherwise don't
- * go looking for one.
- */
- rdp->gpnum = rnp->gpnum;
- trace_rcu_grace_period(rsp->name, rdp->gpnum, "cpustart");
- rdp->passed_quiesce = 0;
- rdp->qs_pending = !!(rnp->qsmask & rdp->grpmask);
- zero_cpu_stall_ticks(rdp);
- }
-}
-
-static void note_new_gpnum(struct rcu_state *rsp, struct rcu_data *rdp)
-{
- unsigned long flags;
- struct rcu_node *rnp;
-
- local_irq_save(flags);
- rnp = rdp->mynode;
- if (rdp->gpnum == ACCESS_ONCE(rnp->gpnum) || /* outside lock. */
- !raw_spin_trylock(&rnp->lock)) { /* irqs already off, so later. */
- local_irq_restore(flags);
- return;
- }
- __note_new_gpnum(rsp, rnp, rdp);
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
-}
-
-/*
- * Did someone else start a new RCU grace period start since we last
- * checked? Update local state appropriately if so. Must be called
- * on the CPU corresponding to rdp.
- */
-static int
-check_for_new_grace_period(struct rcu_state *rsp, struct rcu_data *rdp)
-{
- unsigned long flags;
- int ret = 0;
-
- local_irq_save(flags);
- if (rdp->gpnum != rsp->gpnum) {
- note_new_gpnum(rsp, rdp);
- ret = 1;
- }
- local_irq_restore(flags);
- return ret;
-}
-
/*
* Initialize the specified rcu_data structure's callback list to empty.
*/
}
/*
- * Advance this CPU's callbacks, but only if the current grace period
- * has ended. This may be called only from the CPU to whom the rdp
- * belongs. In addition, the corresponding leaf rcu_node structure's
- * ->lock must be held by the caller, with irqs disabled.
+ * Update CPU-local rcu_data state to record the beginnings and ends of
+ * grace periods. The caller must hold the ->lock of the leaf rcu_node
+ * structure corresponding to the current CPU, and must have irqs disabled.
*/
-static void
-__rcu_process_gp_end(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp)
+static void __note_gp_changes(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp)
{
- /* Did another grace period end? */
+ /* Handle the ends of any preceding grace periods first. */
if (rdp->completed == rnp->completed) {
- /* No, so just accelerate recent callbacks. */
+ /* No grace period end, so just accelerate recent callbacks. */
rcu_accelerate_cbs(rsp, rnp, rdp);
} else {
/* Remember that we saw this grace-period completion. */
rdp->completed = rnp->completed;
trace_rcu_grace_period(rsp->name, rdp->gpnum, "cpuend");
+ }
+ if (rdp->gpnum != rnp->gpnum) {
/*
- * If we were in an extended quiescent state, we may have
- * missed some grace periods that others CPUs handled on
- * our behalf. Catch up with this state to avoid noting
- * spurious new grace periods. If another grace period
- * has started, then rnp->gpnum will have advanced, so
- * we will detect this later on. Of course, any quiescent
- * states we found for the old GP are now invalid.
- */
- if (ULONG_CMP_LT(rdp->gpnum, rdp->completed)) {
- rdp->gpnum = rdp->completed;
- rdp->passed_quiesce = 0;
- }
-
- /*
- * If RCU does not need a quiescent state from this CPU,
- * then make sure that this CPU doesn't go looking for one.
+ * If the current grace period is waiting for this CPU,
+ * set up to detect a quiescent state, otherwise don't
+ * go looking for one.
*/
- if ((rnp->qsmask & rdp->grpmask) == 0)
- rdp->qs_pending = 0;
+ rdp->gpnum = rnp->gpnum;
+ trace_rcu_grace_period(rsp->name, rdp->gpnum, "cpustart");
+ rdp->passed_quiesce = 0;
+ rdp->qs_pending = !!(rnp->qsmask & rdp->grpmask);
+ zero_cpu_stall_ticks(rdp);
}
}
-/*
- * Advance this CPU's callbacks, but only if the current grace period
- * has ended. This may be called only from the CPU to whom the rdp
- * belongs.
- */
-static void
-rcu_process_gp_end(struct rcu_state *rsp, struct rcu_data *rdp)
+static void note_gp_changes(struct rcu_state *rsp, struct rcu_data *rdp)
{
unsigned long flags;
struct rcu_node *rnp;
local_irq_save(flags);
rnp = rdp->mynode;
- if (rdp->completed == ACCESS_ONCE(rnp->completed) || /* outside lock. */
+ if ((rdp->gpnum == ACCESS_ONCE(rnp->gpnum) &&
+ rdp->completed == ACCESS_ONCE(rnp->completed)) || /* w/out lock. */
!raw_spin_trylock(&rnp->lock)) { /* irqs already off, so later. */
local_irq_restore(flags);
return;
}
- __rcu_process_gp_end(rsp, rnp, rdp);
+ __note_gp_changes(rsp, rnp, rdp);
raw_spin_unlock_irqrestore(&rnp->lock, flags);
}
-/*
- * Do per-CPU grace-period initialization for running CPU. The caller
- * must hold the lock of the leaf rcu_node structure corresponding to
- * this CPU.
- */
-static void
-rcu_start_gp_per_cpu(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp)
-{
- /* Prior grace period ended, so advance callbacks for current CPU. */
- __rcu_process_gp_end(rsp, rnp, rdp);
-
- /* Set state so that this CPU will detect the next quiescent state. */
- __note_new_gpnum(rsp, rnp, rdp);
-}
-
/*
* Initialize a new grace period.
*/
WARN_ON_ONCE(rnp->completed != rsp->completed);
ACCESS_ONCE(rnp->completed) = rsp->completed;
if (rnp == rdp->mynode)
- rcu_start_gp_per_cpu(rsp, rnp, rdp);
+ __note_gp_changes(rsp, rnp, rdp);
rcu_preempt_boost_start_gp(rnp);
trace_rcu_grace_period_init(rsp->name, rnp->gpnum,
rnp->level, rnp->grplo,
ACCESS_ONCE(rnp->completed) = rsp->gpnum;
rdp = this_cpu_ptr(rsp->rda);
if (rnp == rdp->mynode)
- __rcu_process_gp_end(rsp, rnp, rdp);
+ __note_gp_changes(rsp, rnp, rdp);
nocb += rcu_future_gp_cleanup(rsp, rnp);
raw_spin_unlock_irq(&rnp->lock);
cond_resched();
static void
rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp)
{
- /* If there is now a new grace period, record and return. */
- if (check_for_new_grace_period(rsp, rdp))
- return;
+ /* Check for grace-period ends and beginnings. */
+ note_gp_changes(rsp, rdp);
/*
* Does this CPU still need to do its part for current grace period?
WARN_ON_ONCE(rdp->beenonline == 0);
- /* Handle the end of a grace period that some other CPU ended. */
- rcu_process_gp_end(rsp, rdp);
-
/* Update RCU state based on any recent quiescent states. */
rcu_check_quiescent_state(rsp, rdp);
if (unlikely(rdp->qlen > rdp->qlen_last_fqs_check + qhimark)) {
/* Are we ignoring a completed grace period? */
- rcu_process_gp_end(rsp, rdp);
- check_for_new_grace_period(rsp, rdp);
+ note_gp_changes(rsp, rdp);
/* Start a new grace period if one not already started. */
if (!rcu_gp_in_progress(rsp)) {
*/
static void __init rcu_init_geometry(void)
{
+ ulong d;
int i;
int j;
int n = nr_cpu_ids;
int rcu_capacity[MAX_RCU_LVLS + 1];
+ /*
+ * Initialize any unspecified boot parameters.
+ * The default values of jiffies_till_first_fqs and
+ * jiffies_till_next_fqs are set to the RCU_JIFFIES_TILL_FORCE_QS
+ * value, which is a function of HZ, then adding one for each
+ * RCU_JIFFIES_FQS_DIV CPUs that might be on the system.
+ */
+ d = RCU_JIFFIES_TILL_FORCE_QS + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
+ if (jiffies_till_first_fqs == ULONG_MAX)
+ jiffies_till_first_fqs = d;
+ if (jiffies_till_next_fqs == ULONG_MAX)
+ jiffies_till_next_fqs = d;
+
/* If the compile-time values are accurate, just leave. */
if (rcu_fanout_leaf == CONFIG_RCU_FANOUT_LEAF &&
nr_cpu_ids == NR_CPUS)
#define RCU_FORCE_QS 3 /* Need to force quiescent state. */
#define RCU_SIGNAL_INIT RCU_SAVE_DYNTICK
-#define RCU_JIFFIES_TILL_FORCE_QS 3 /* for rsp->jiffies_force_qs */
+#define RCU_JIFFIES_TILL_FORCE_QS (1 + (HZ > 250) + (HZ > 500))
+ /* For jiffies_till_first_fqs and */
+ /* and jiffies_till_next_fqs. */
-#define RCU_STALL_RAT_DELAY 2 /* Allow other CPUs time */
- /* to take at least one */
- /* scheduling clock irq */
- /* before ratting on them. */
+#define RCU_JIFFIES_FQS_DIV 256 /* Very large systems need more */
+ /* delay between bouts of */
+ /* quiescent-state forcing. */
+
+#define RCU_STALL_RAT_DELAY 2 /* Allow other CPUs time to take */
+ /* at least one scheduling clock */
+ /* irq before ratting on them. */
#define rcu_wait(cond) \
do { \
static void __init rcu_bootup_announce_oddness(void)
{
#ifdef CONFIG_RCU_TRACE
- printk(KERN_INFO "\tRCU debugfs-based tracing is enabled.\n");
+ pr_info("\tRCU debugfs-based tracing is enabled.\n");
#endif
#if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32)
- printk(KERN_INFO "\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
+ pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
CONFIG_RCU_FANOUT);
#endif
#ifdef CONFIG_RCU_FANOUT_EXACT
- printk(KERN_INFO "\tHierarchical RCU autobalancing is disabled.\n");
+ pr_info("\tHierarchical RCU autobalancing is disabled.\n");
#endif
#ifdef CONFIG_RCU_FAST_NO_HZ
- printk(KERN_INFO
- "\tRCU dyntick-idle grace-period acceleration is enabled.\n");
+ pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");
#endif
#ifdef CONFIG_PROVE_RCU
- printk(KERN_INFO "\tRCU lockdep checking is enabled.\n");
+ pr_info("\tRCU lockdep checking is enabled.\n");
#endif
#ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE
- printk(KERN_INFO "\tRCU torture testing starts during boot.\n");
+ pr_info("\tRCU torture testing starts during boot.\n");
#endif
#if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE)
- printk(KERN_INFO "\tDump stacks of tasks blocking RCU-preempt GP.\n");
+ pr_info("\tDump stacks of tasks blocking RCU-preempt GP.\n");
#endif
#if defined(CONFIG_RCU_CPU_STALL_INFO)
- printk(KERN_INFO "\tAdditional per-CPU info printed with stalls.\n");
+ pr_info("\tAdditional per-CPU info printed with stalls.\n");
#endif
#if NUM_RCU_LVL_4 != 0
- printk(KERN_INFO "\tFour-level hierarchy is enabled.\n");
+ pr_info("\tFour-level hierarchy is enabled.\n");
#endif
if (rcu_fanout_leaf != CONFIG_RCU_FANOUT_LEAF)
- printk(KERN_INFO "\tExperimental boot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);
+ pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);
if (nr_cpu_ids != NR_CPUS)
- printk(KERN_INFO "\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids);
+ pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids);
#ifdef CONFIG_RCU_NOCB_CPU
#ifndef CONFIG_RCU_NOCB_CPU_NONE
if (!have_rcu_nocb_mask) {
have_rcu_nocb_mask = true;
}
#ifdef CONFIG_RCU_NOCB_CPU_ZERO
- pr_info("\tExperimental no-CBs CPU 0\n");
+ pr_info("\tOffload RCU callbacks from CPU 0\n");
cpumask_set_cpu(0, rcu_nocb_mask);
#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */
#ifdef CONFIG_RCU_NOCB_CPU_ALL
- pr_info("\tExperimental no-CBs for all CPUs\n");
+ pr_info("\tOffload RCU callbacks from all CPUs\n");
cpumask_setall(rcu_nocb_mask);
#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */
#endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */
if (have_rcu_nocb_mask) {
cpulist_scnprintf(nocb_buf, sizeof(nocb_buf), rcu_nocb_mask);
- pr_info("\tExperimental no-CBs CPUs: %s.\n", nocb_buf);
+ pr_info("\tOffload RCU callbacks from CPUs: %s.\n", nocb_buf);
if (rcu_nocb_poll)
- pr_info("\tExperimental polled no-CBs CPUs.\n");
+ pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
}
#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
}
*/
static void __init rcu_bootup_announce(void)
{
- printk(KERN_INFO "Preemptible hierarchical RCU implementation.\n");
+ pr_info("Preemptible hierarchical RCU implementation.\n");
rcu_bootup_announce_oddness();
}
static void rcu_print_task_stall_begin(struct rcu_node *rnp)
{
- printk(KERN_ERR "\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
+ pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
rnp->level, rnp->grplo, rnp->grphi);
}
static void rcu_print_task_stall_end(void)
{
- printk(KERN_CONT "\n");
+ pr_cont("\n");
}
#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
t = list_entry(rnp->gp_tasks,
struct task_struct, rcu_node_entry);
list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
- printk(KERN_CONT " P%d", t->pid);
+ pr_cont(" P%d", t->pid);
ndetected++;
}
rcu_print_task_stall_end();
rcu_init_one(&rcu_preempt_state, &rcu_preempt_data);
}
+/*
+ * Check for a task exiting while in a preemptible-RCU read-side
+ * critical section, clean up if so. No need to issue warnings,
+ * as debug_check_no_locks_held() already does this if lockdep
+ * is enabled.
+ */
+void exit_rcu(void)
+{
+ struct task_struct *t = current;
+
+ if (likely(list_empty(¤t->rcu_node_entry)))
+ return;
+ t->rcu_read_lock_nesting = 1;
+ barrier();
+ t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED;
+ __rcu_read_unlock();
+}
+
#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
static struct rcu_state *rcu_state = &rcu_sched_state;
*/
static void __init rcu_bootup_announce(void)
{
- printk(KERN_INFO "Hierarchical RCU implementation.\n");
+ pr_info("Hierarchical RCU implementation.\n");
rcu_bootup_announce_oddness();
}
{
}
+/*
+ * Because preemptible RCU does not exist, tasks cannot possibly exit
+ * while in preemptible RCU read-side critical sections.
+ */
+void exit_rcu(void)
+{
+}
+
#endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
#ifdef CONFIG_RCU_BOOST
*/
if (rdp->completed != rnp->completed &&
rdp->nxttail[RCU_DONE_TAIL] != rdp->nxttail[RCU_NEXT_TAIL])
- rcu_process_gp_end(rsp, rdp);
+ note_gp_changes(rsp, rdp);
if (cpu_has_callbacks_ready_to_invoke(rdp))
cbs_ready = true;
/* Initiate the stall-info list. */
static void print_cpu_stall_info_begin(void)
{
- printk(KERN_CONT "\n");
+ pr_cont("\n");
}
/*
ticks_value = rsp->gpnum - rdp->gpnum;
}
print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
- printk(KERN_ERR "\t%d: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u %s\n",
+ pr_err("\t%d: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u %s\n",
cpu, ticks_value, ticks_title,
atomic_read(&rdtp->dynticks) & 0xfff,
rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
/* Terminate the stall-info list. */
static void print_cpu_stall_info_end(void)
{
- printk(KERN_ERR "\t");
+ pr_err("\t");
}
/* Zero ->ticks_this_gp for all flavors of RCU. */
static void print_cpu_stall_info_begin(void)
{
- printk(KERN_CONT " {");
+ pr_cont(" {");
}
static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
{
- printk(KERN_CONT " %d", cpu);
+ pr_cont(" %d", cpu);
}
static void print_cpu_stall_info_end(void)
{
- printk(KERN_CONT "} ");
+ pr_cont("} ");
}
static void zero_cpu_stall_ticks(struct rcu_data *rdp)
projects / karo-tx-linux.git / commitdiff