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author | Frederic Weisbecker <fweisbec@gmail.com> | 2011-12-23 04:25:23 +0100 |
---|---|---|
committer | Tejun Heo <tj@kernel.org> | 2011-12-27 18:05:20 +0100 |
commit | 7e3aa30ac8c904a706518b725c451bb486daaae9 (patch) | |
tree | 1a6ad0678271d1cba5eba2fcafcbfa71b4e4c66d /kernel/cgroup.c | |
parent | cgroup: add sparse annotation to cgroup_iter_start() and cgroup_iter_end() (diff) | |
download | linux-7e3aa30ac8c904a706518b725c451bb486daaae9.tar.xz linux-7e3aa30ac8c904a706518b725c451bb486daaae9.zip |
cgroup: Remove task_lock() from cgroup_post_fork()
cgroup_post_fork() is protected between threadgroup_change_begin()
and threadgroup_change_end() against concurrent changes of the
child's css_set in cgroup_task_migrate(). Also the child can't
exit and call cgroup_exit() at this stage, this means it's css_set
can't be changed with init_css_set concurrently.
For these reasons, we don't need to hold task_lock() on the child
because it's css_set can only remain stable in this place.
Let's remove the lock there.
v2: Update comment to explain that we are safe against
cgroup_exit()
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Containers <containers@lists.linux-foundation.org>
Cc: Cgroups <cgroups@vger.kernel.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Paul Menage <paul@paulmenage.org>
Cc: Mandeep Singh Baines <msb@chromium.org>
Diffstat (limited to 'kernel/cgroup.c')
-rw-r--r-- | kernel/cgroup.c | 15 |
1 files changed, 12 insertions, 3 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c index c6bd67b3fcf6..548d8d4e86d0 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -4595,10 +4595,19 @@ void cgroup_post_fork(struct task_struct *child) { if (use_task_css_set_links) { write_lock(&css_set_lock); - task_lock(child); - if (list_empty(&child->cg_list)) + if (list_empty(&child->cg_list)) { + /* + * It's safe to use child->cgroups without task_lock() + * here because we are protected through + * threadgroup_change_begin() against concurrent + * css_set change in cgroup_task_migrate(). Also + * the task can't exit at that point until + * wake_up_new_task() is called, so we are protected + * against cgroup_exit() setting child->cgroup to + * init_css_set. + */ list_add(&child->cg_list, &child->cgroups->tasks); - task_unlock(child); + } write_unlock(&css_set_lock); } } |