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authorTejun Heo <tj@kernel.org>2012-10-18 17:52:07 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2012-10-28 10:14:14 -0700
commit727fa37e405a71dc1c7208ea7352be55e0310eca (patch)
tree43de8999a864592379df86384426ad2ebf1038fa /kernel
parent5993bba302a1a6df9c73690a08346411ff7cd56e (diff)
Revert "cgroup: Drop task_lock(parent) on cgroup_fork()"
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 <tj@kernel.org> LKML-Reference: <20121008020000.GB2575@localhost> Acked-by: Li Zefan <lizefan@huawei.com> Bitterly-Acked-by: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/cgroup.c23
1 files changed, 6 insertions, 17 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 5cb488065dca..762f7cc753ac 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4462,31 +4462,20 @@ 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);
}