Messages in this thread Patch in this message | | | From | Herton Ronaldo Krzesinski <> | Subject | [PATCH 198/270] Revert "cgroup: Remove task_lock() from cgroup_post_fork()" | Date | Mon, 26 Nov 2012 14:58:08 -0200 |
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3.5.7u1 -stable review patch. If anyone has any objections, please let me know.
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From: Tejun Heo <tj@kernel.org>
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 <tj@kernel.org> LKML-Reference: <20121008020000.GB2575@localhost> Acked-by: Li Zefan <lizefan@huawei.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski@canonical.com> --- kernel/cgroup.c | 15 +++------------ 1 file changed, 3 insertions(+), 12 deletions(-)
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); } } -- 1.7.9.5
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