Merge tag 'cgroup-for-7.1-rc2-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup

Pull cgroup fixes from Tejun Heo:

 - During v6.19, cgroup task unlink was moved from do_exit() to after the
   final task switch to satisfy a controller invariant. That left the kernel
   seeing tasks past exit_signals() longer than userspace expected, and
   several v7.0 follow-ups tried to bridge the gap by making rmdir wait for
   the kernel side. None held up.

   The latest is an A-A deadlock when rmdir is invoked by the reaper of
   zombies whose pidns teardown the rmdir itself is waiting on, which
   points at the synchronizing approach being fundamentally wrong.

   Take a different approach: drop the wait, leave rmdir's user-visible
   side returning as soon as cgroup.procs is empty, and defer the css
   percpu_ref kill that drives ->css_offline() until the cgroup is fully
   depopulated.

   Tagged for stable. Somewhat invasive but contained. The hope is that
   fixing forward sticks. If not, the fallback is to revert the entire
   chain and rework on the development branch.

   Note that this doesn't plug a pre-existing analogous race in
   cgroup_apply_control_disable() (controller disable via
   subtree_control). Not a regression. The development branch will do
   the more invasive restructuring needed for that.

 - Documentation update for cgroup-v1 charge-commit section that still
   referenced functions removed when the memcg hugetlb try-commit-cancel
   protocol was retired.

* tag 'cgroup-for-7.1-rc2-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
  docs: cgroup-v1: Update charge-commit section
  cgroup: Defer css percpu_ref kill on rmdir until cgroup is depopulated

1 files changed, 2 insertions, 2 deletions

diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index f42563739d2e..50a784da7a81 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -611,8 +611,8 @@ struct cgroup {
 	/* used to wait for offlining of csses */
 	wait_queue_head_t offline_waitq;
 
-	/* used by cgroup_rmdir() to wait for dying tasks to leave */
-	wait_queue_head_t dying_populated_waitq;
+	/* defers killing csses after removal until cgroup is depopulated */
+	struct work_struct finish_destroy_work;
 
 	/* used to schedule release agent */
 	struct work_struct release_agent_work;