path: root/kernel
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authorTejun Heo <tj@kernel.org>2012-10-18 17:40:30 -0700
committerTejun Heo <tj@kernel.org>2012-10-19 14:09:35 -0700
commitd87838321124061f6c935069d97f37010fa417e6 (patch)
tree825e291d0ad7bdc7e7eb68e4bb829121de2586bc /kernel
parent9bb71308b8133d643648776243e4d5599b1c193d (diff)
Revert "cgroup: Remove task_lock() from cgroup_post_fork()"
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> Cc: stable@vger.kernel.org
Diffstat (limited to 'kernel')
1 files changed, 3 insertions, 12 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 75aec12c78a..f24f724620d 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4883,19 +4883,10 @@ void cgroup_post_fork(struct task_struct *child)
if (use_task_css_set_links) {
- 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);