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Date: Wed, 1 Nov 2017 22:17:40 +0100 From: Willy Tarreau <w@....eu> To: linux-kernel@...r.kernel.org, stable@...r.kernel.org, linux@...ck-us.net Cc: Tejun Heo <tj@...nel.org>, Willy Tarreau <w@....eu> Subject: [PATCH 3.10 040/139] workqueue: restore WQ_UNBOUND/max_active==1 to be ordered From: Tejun Heo <tj@...nel.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@...nel.org> Reported-by: Christoph Hellwig <hch@...radead.org> Reported-by: Alexei Potashnik <alexei@...estorage.com> Fixes: 4c16bd327c74 ("workqueue: implement NUMA affinity for unbound workqueues") Cc: stable@...r.kernel.org Signed-off-by: Willy Tarreau <w@....eu> --- kernel/workqueue.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 66972ac..3f8558f 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -4213,6 +4213,16 @@ struct workqueue_struct *__alloc_workqueue_key(const char *fmt, 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; + /* allocate wq and format name */ if (flags & WQ_UNBOUND) tbl_size = wq_numa_tbl_len * sizeof(wq->numa_pwq_tbl[0]); -- 2.8.0.rc2.1.gbe9624a
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