From mboxrd@z Thu Jan 1 00:00:00 1970 From: Frederic Weisbecker Subject: [PATCH 2/2] cgroup: Drop task_lock(parent) on cgroup_fork() Date: Tue, 20 Dec 2011 20:01:13 +0100 Message-ID: <1324407673-18975-2-git-send-email-fweisbec@gmail.com> References: <1324320274-18485-1-git-send-email-msb@chromium.org> <1324407673-18975-1-git-send-email-fweisbec@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=from:to:cc:subject:date:message-id:x-mailer:in-reply-to:references; bh=W3+8p043x0NKfpFzuuyD7GDuQX04IboN7OGOYgXr3kk=; b=qnqIuJzIDJal5dvetACwyUavDPYD4Hmb5saFAp+INvoNoiUK+rUjG7/Rj0/V+7Z8me MJT9b+v2GiooOzfs8QJb7SCdtgo0gGrxaacLX9eZYs4R+jCovo3Iz55H92UScvf+drNL nViGd6Qc35ndFaAZRBSbiQ93tmwwTORTiPRSs= In-Reply-To: <1324407673-18975-1-git-send-email-fweisbec-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Tejun Heo , Li Zefan Cc: Frederic Weisbecker , Containers , Oleg Nesterov , LKML , Mandeep Singh Baines , Cgroups , Andrew Morton , Paul Menage 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 Cc: Tejun Heo Cc: Li Zefan Cc: Containers Cc: Cgroups Cc: KAMEZAWA Hiroyuki Cc: Oleg Nesterov Cc: Andrew Morton Cc: Paul Menage Cc: Mandeep Singh Baines --- kernel/cgroup.c | 10 +++++++--- 1 files changed, 7 insertions(+), 3 deletions(-) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 6b5f693..a1e87a4 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -4544,7 +4544,7 @@ 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. @@ -4554,10 +4554,14 @@ 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