From patchwork Thu Nov 22 04:46:37 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: [3.5.yuz, extended, stable] Patch "Revert "cgroup: Remove task_lock() from cgroup_post_fork()"" has been added to staging queue Date: Wed, 21 Nov 2012 18:46:37 -0000 From: Herton Ronaldo Krzesinski X-Patchwork-Id: 200953 Message-Id: <1353559597-378-1-git-send-email-herton.krzesinski@canonical.com> To: Tejun Heo Cc: Frederic Weisbecker , kernel-team@lists.ubuntu.com, Li Zefan This is a note to let you know that I have just added a patch titled Revert "cgroup: Remove task_lock() from cgroup_post_fork()" to the linux-3.5.y-queue branch of the 3.5.yuz extended stable tree which can be found at: http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.5.yuz tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Herton ------ >From ef501122155212d6193bc95b82ef86828e56aad2 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Thu, 18 Oct 2012 17:40:30 -0700 Subject: [PATCH] Revert "cgroup: Remove task_lock() from cgroup_post_fork()" commit d87838321124061f6c935069d97f37010fa417e6 upstream. This reverts commit 7e3aa30ac8c904a706518b725c451bb486daaae9. The commit incorrectly assumed that fork path always performed threadgroup_change_begin/end() and depended on that for synchronization against task exit and cgroup migration paths instead of explicitly grabbing task_lock(). threadgroup_change is not locked when forking a new process (as opposed to a new thread in the same process) and even if it were it wouldn't be effective as different processes use different threadgroup locks. Revert the incorrect optimization. Signed-off-by: Tejun Heo LKML-Reference: <20121008020000.GB2575@localhost> Acked-by: Li Zefan Cc: Frederic Weisbecker Signed-off-by: Herton Ronaldo Krzesinski --- kernel/cgroup.c | 15 +++------------ 1 file changed, 3 insertions(+), 12 deletions(-) -- 1.7.9.5 diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 75d4318..a91aa0b 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -4805,19 +4805,10 @@ void cgroup_post_fork(struct task_struct *child) */ if (use_task_css_set_links) { write_lock(&css_set_lock); - 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. - */ + task_lock(child); + if (list_empty(&child->cg_list)) list_add(&child->cg_list, &child->cgroups->tasks); - } + task_unlock(child); write_unlock(&css_set_lock); } }