Messages in this thread Patch in this message | | | From | Herton Ronaldo Krzesinski <> | Subject | [PATCH 197/270] Revert "cgroup: Drop task_lock(parent) on cgroup_fork()" | Date | Mon, 26 Nov 2012 14:58:07 -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 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: Herton Ronaldo Krzesinski <herton.krzesinski@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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