From e93ad19d05648397ef3bcb838d26aec06c245dc0 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Tue, 19 Jan 2016 12:18:41 -0500 Subject: cpuset: make mm migration asynchronous If "cpuset.memory_migrate" is set, when a process is moved from one cpuset to another with a different memory node mask, pages in used by the process are migrated to the new set of nodes. This was performed synchronously in the ->attach() callback, which is synchronized against process management. Recently, the synchronization was changed from per-process rwsem to global percpu rwsem for simplicity and optimization. Combined with the synchronous mm migration, this led to deadlocks because mm migration could schedule a work item which may in turn try to create a new worker blocking on the process management lock held from cgroup process migration path. This heavy an operation shouldn't be performed synchronously from that deep inside cgroup migration in the first place. This patch punts the actual migration to an ordered workqueue and updates cgroup process migration and cpuset config update paths to flush the workqueue after all locks are released. This way, the operations still seem synchronous to userland without entangling mm migration with process management synchronization. CPU hotplug can also invoke mm migration but there's no reason for it to wait for mm migrations and thus doesn't synchronize against their completions. Signed-off-by: Tejun Heo Reported-and-tested-by: Christian Borntraeger Cc: stable@vger.kernel.org # v4.4+ --- kernel/cgroup.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'kernel/cgroup.c') diff --git a/kernel/cgroup.c b/kernel/cgroup.c index c03a640ef6da..88abd4d076d8 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -58,6 +58,7 @@ #include #include #include +#include #include /* @@ -2739,6 +2740,7 @@ out_unlock_rcu: out_unlock_threadgroup: percpu_up_write(&cgroup_threadgroup_rwsem); cgroup_kn_unlock(of->kn); + cpuset_post_attach_flush(); return ret ?: nbytes; } -- cgit v1.2.3