| From 5c0338c68706be53b3dc472e4308961c36e4ece1 Mon Sep 17 00:00:00 2001 |
| From: Tejun Heo <tj@kernel.org> |
| Date: Tue, 18 Jul 2017 18:41:52 -0400 |
| Subject: workqueue: restore WQ_UNBOUND/max_active==1 to be ordered |
| |
| From: Tejun Heo <tj@kernel.org> |
| |
| commit 5c0338c68706be53b3dc472e4308961c36e4ece1 upstream. |
| |
| The combination of WQ_UNBOUND and max_active == 1 used to imply |
| ordered execution. After NUMA affinity 4c16bd327c74 ("workqueue: |
| implement NUMA affinity for unbound workqueues"), this is no longer |
| true due to per-node worker pools. |
| |
| While the right way to create an ordered workqueue is |
| alloc_ordered_workqueue(), the documentation has been misleading for a |
| long time and people do use WQ_UNBOUND and max_active == 1 for ordered |
| workqueues which can lead to subtle bugs which are very difficult to |
| trigger. |
| |
| It's unlikely that we'd see noticeable performance impact by enforcing |
| ordering on WQ_UNBOUND / max_active == 1 workqueues. Let's |
| automatically set __WQ_ORDERED for those workqueues. |
| |
| Signed-off-by: Tejun Heo <tj@kernel.org> |
| Reported-by: Christoph Hellwig <hch@infradead.org> |
| Reported-by: Alexei Potashnik <alexei@purestorage.com> |
| Fixes: 4c16bd327c74 ("workqueue: implement NUMA affinity for unbound workqueues") |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| kernel/workqueue.c | 10 ++++++++++ |
| 1 file changed, 10 insertions(+) |
| |
| --- a/kernel/workqueue.c |
| +++ b/kernel/workqueue.c |
| @@ -3834,6 +3834,16 @@ struct workqueue_struct *__alloc_workque |
| struct workqueue_struct *wq; |
| struct pool_workqueue *pwq; |
| |
| + /* |
| + * Unbound && max_active == 1 used to imply ordered, which is no |
| + * longer the case on NUMA machines due to per-node pools. While |
| + * alloc_ordered_workqueue() is the right way to create an ordered |
| + * workqueue, keep the previous behavior to avoid subtle breakages |
| + * on NUMA. |
| + */ |
| + if ((flags & WQ_UNBOUND) && max_active == 1) |
| + flags |= __WQ_ORDERED; |
| + |
| /* see the comment above the definition of WQ_POWER_EFFICIENT */ |
| if ((flags & WQ_POWER_EFFICIENT) && wq_power_efficient) |
| flags |= WQ_UNBOUND; |
