From b5d9cfcb1fe90419ff31ef5a644d36ee3104e94d Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Wed, 12 Feb 2014 19:06:19 -0500 Subject: [PATCH] Revert "cgroup: use an ordered workqueue for cgroup destruction" This reverts commit c91287880d1921730b7d464008543ad754ca1e95. Explanation from Hugh: It's because more thorough testing, by others here, found that it wasn't always solving the problem: so I asked Tejun privately to hold off from sending it in, until we'd worked out why not. Most of our testing being on a v3,11-based kernel, it was perfectly possible that the problem was merely our own e.g. missing Tejun's c051bcb86914 ("workqueue: fix ordered workqueues in NUMA setups"). But that turned out not to be enough to fix it either. Then Filipe pointed out how percpu_ref_kill_and_confirm() uses call_rcu_sched() before we ever get to put the offline on to the workqueue: by the time we get to the workqueue, the ordering has already been lost. So, thanks for the Acks, but I'm afraid that this ordered workqueue solution is just not good enough: we should simply forget that patch and provide a different answer." Signed-off-by: Tejun Heo Cc: Hugh Dickins --- kernel/cgroup.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 52719ce55dd3d..68d87103b493a 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -4844,16 +4844,12 @@ static int __init cgroup_wq_init(void) /* * There isn't much point in executing destruction path in * parallel. Good chunk is serialized with cgroup_mutex anyway. - * - * XXX: Must be ordered to make sure parent is offlined after - * children. The ordering requirement is for memcg where a - * parent's offline may wait for a child's leading to deadlock. In - * the long term, this should be fixed from memcg side. + * Use 1 for @max_active. * * We would prefer to do this in cgroup_init() above, but that * is called before init_workqueues(): so leave this until after. */ - cgroup_destroy_wq = alloc_ordered_workqueue("cgroup_destroy", 0); + cgroup_destroy_wq = alloc_workqueue("cgroup_destroy", 0, 1); BUG_ON(!cgroup_destroy_wq); /* -- 2.39.5