From 452477fa68c6d8ef80adebd05194c1c157ad9a53 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 7 Jan 2013 08:51:07 -0800 Subject: [PATCH] cpuset: pin down cpus and mems while a task is being attached cpuset is scheduled to be decoupled from cgroup_lock which will make configuration updates race with task migration. Any config update will be allowed to happen between ->can_attach() and ->attach(). If such config update removes either all cpus or mems, by the time ->attach() is called, the condition verified by ->can_attach(), that the cpuset is capable of hosting the tasks, is no longer true. This patch adds cpuset->attach_in_progress which is incremented from ->can_attach() and decremented when the attach operation finishes either successfully or not. validate_change() treats cpusets w/ non-zero ->attach_in_progress like cpusets w/ tasks and refuses to remove all cpus or mems from it. This currently doesn't make any functional difference as everything is protected by cgroup_mutex but enables decoupling the locking. Signed-off-by: Tejun Heo Acked-by: Li Zefan --- kernel/cpuset.c | 28 ++++++++++++++++++++++++++-- 1 file changed, 26 insertions(+), 2 deletions(-) diff --git a/kernel/cpuset.c b/kernel/cpuset.c index a7bb547786d7..4334576f5d6a 100644 --- a/kernel/cpuset.c +++ b/kernel/cpuset.c @@ -91,6 +91,12 @@ struct cpuset { struct fmeter fmeter; /* memory_pressure filter */ + /* + * Tasks are being attached to this cpuset. Used to prevent + * zeroing cpus/mems_allowed between ->can_attach() and ->attach(). + */ + int attach_in_progress; + /* partition number for rebuild_sched_domains() */ int pn; @@ -468,9 +474,12 @@ static int validate_change(const struct cpuset *cur, const struct cpuset *trial) goto out; } - /* Cpusets with tasks can't have empty cpus_allowed or mems_allowed */ + /* + * Cpusets with tasks - existing or newly being attached - can't + * have empty cpus_allowed or mems_allowed. + */ ret = -ENOSPC; - if (cgroup_task_count(cur->css.cgroup) && + if ((cgroup_task_count(cur->css.cgroup) || cur->attach_in_progress) && (cpumask_empty(trial->cpus_allowed) || nodes_empty(trial->mems_allowed))) goto out; @@ -1386,9 +1395,21 @@ static int cpuset_can_attach(struct cgroup *cgrp, struct cgroup_taskset *tset) return ret; } + /* + * Mark attach is in progress. This makes validate_change() fail + * changes which zero cpus/mems_allowed. + */ + cs->attach_in_progress++; + return 0; } +static void cpuset_cancel_attach(struct cgroup *cgrp, + struct cgroup_taskset *tset) +{ + cgroup_cs(cgrp)->attach_in_progress--; +} + /* * Protected by cgroup_mutex. cpus_attach is used only by cpuset_attach() * but we can't allocate it dynamically there. Define it global and @@ -1441,6 +1462,8 @@ static void cpuset_attach(struct cgroup *cgrp, struct cgroup_taskset *tset) &cpuset_attach_nodemask_to); mmput(mm); } + + cs->attach_in_progress--; } /* The various types of files and directories in a cpuset file system */ @@ -1908,6 +1931,7 @@ struct cgroup_subsys cpuset_subsys = { .css_offline = cpuset_css_offline, .css_free = cpuset_css_free, .can_attach = cpuset_can_attach, + .cancel_attach = cpuset_cancel_attach, .attach = cpuset_attach, .subsys_id = cpuset_subsys_id, .base_cftypes = files, -- 2.39.5