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Date: Wed, 21 Dec 2011 03:02:38 +0100 From: Frederic Weisbecker <fweisbec@...il.com> To: Tejun Heo <tj@...nel.org>, Li Zefan <lizf@...fujitsu.com> Cc: LKML <linux-kernel@...r.kernel.org>, Frederic Weisbecker <fweisbec@...il.com>, Containers <containers@...ts.linux-foundation.org>, Cgroups <cgroups@...r.kernel.org>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>, Oleg Nesterov <oleg@...hat.com>, Andrew Morton <akpm@...ux-foundation.org>, Paul Menage <paul@...lmenage.org>, Mandeep Singh Baines <msb@...omium.org> Subject: [PATCH 2/2 v2] cgroup: Drop task_lock(parent) on cgroup_fork() We don't need to hold the parent task_lock() on the parent in cgroup_fork() because we are already synchronized against the two places that may change the parent css_set concurrently: - cgroup_exit(), but the parent obviously can't exit concurrently - cgroup migration: we are synchronized against threadgroup_lock() So we can safely remove the task_lock() there. Signed-off-by: Frederic Weisbecker <fweisbec@...il.com> Cc: Tejun Heo <tj@...nel.org> Cc: Li Zefan <lizf@...fujitsu.com> Cc: Containers <containers@...ts.linux-foundation.org> Cc: Cgroups <cgroups@...r.kernel.org> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> Cc: Oleg Nesterov <oleg@...hat.com> Cc: Andrew Morton <akpm@...ux-foundation.org> Cc: Paul Menage <paul@...lmenage.org> Cc: Mandeep Singh Baines <msb@...omium.org> --- kernel/cgroup.c | 10 +++++++--- 1 files changed, 7 insertions(+), 3 deletions(-) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 24f6d6f..1999f60 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -4556,7 +4556,7 @@ static const struct file_operations proc_cgroupstats_operations = { * * A pointer to the shared css_set was automatically copied in * fork.c by dup_task_struct(). However, we ignore that copy, since - * it was not made under the protection of RCU or cgroup_mutex, so + * it was not made under the protection of threadgroup_change_begin(), so * might no longer be a valid cgroup pointer. cgroup_attach_task() might * have already changed current->cgroups, allowing the previously * referenced cgroup group to be removed and freed. @@ -4566,10 +4566,14 @@ static const struct file_operations proc_cgroupstats_operations = { */ void cgroup_fork(struct task_struct *child) { - task_lock(current); + /* + * We don't need to task_lock() current because current->cgroups + * can't be changed concurrently here. The parent obviously hasn't + * exited and called cgroup_exit(), and we are synchronized against + * cgroup migration through threadgroup_change_begin(). + */ child->cgroups = current->cgroups; get_css_set(child->cgroups); - task_unlock(current); INIT_LIST_HEAD(&child->cg_list); } -- 1.7.5.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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