3.5.7u1 -stable review patch. If anyone has any objections, please let me know.
------------------
From: Tejun Heo <t...@kernel.org>
commit 9bb71308b8133d643648776243e4d5599b1c193d upstream.
This reverts commit 7e381b0eb1e1a9805c37335562e8dc02e7d7848c.
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 <t...@kernel.org>
LKML-Reference: <20121008020000.GB2575@localhost>
Acked-by: Li Zefan <lize...@huawei.com>
Bitterly-Acked-by: Frederic Weisbecker <fweis...@gmail.com>
Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesin...@canonical.com>
---
kernel/cgroup.c | 23 ++++++-----------------
1 file changed, 6 insertions(+), 17 deletions(-)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 63c9596..75d4318 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4739,31 +4739,20 @@ 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, cgroup_mutex or
- * threadgroup_change_begin(), so it 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.
- *
- * Outside the pointer validity we also need to process the css_set
- * inheritance between threadgoup_change_begin() and
- * threadgoup_change_end(), this way there is no leak in any process
- * wide migration performed by cgroup_attach_proc() that could otherwise
- * miss a thread because it is too early or too late in the fork stage.
+ * it was not made under the protection of RCU or cgroup_mutex, 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.
*
* At the point that cgroup_fork() is called, 'current' is the parent
* task, and the passed argument 'child' points to the child task.
*/
void cgroup_fork(struct task_struct *child)
{
- /*
- * 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().
- */
+ task_lock(current);
child->cgroups = current->cgroups;
get_css_set(child->cgroups);
+ task_unlock(current);
INIT_LIST_HEAD(&child->cg_list);
}
--
1.7.9.5
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