[PATCH] NOCOMMIT: WARNING triggers at blk_mq_update_nr_hw_queues during nvme_reset_work

[Gabriel Krisman Bertazi]

From: Keith Busch <keith.busch at intel.com>

On Tue, May 30, 2017 at 02:00:44PM -0300, Gabriel Krisman Bertazi wrote:
> Since the merge window for 4.12, one of the machines in Intel's CI
> started to hit the WARN_ON below at blk_mq_update_nr_hw_queues during an
> nvme_reset_work.  The issue persists with the latest 4.12-rc3, and full
> dmesg from boot, up to the moment where the WARN_ON triggers is
> available at the following link:
>
> https://intel-gfx-ci.01.org/CI/CI_DRM_2672/fi-kbl-7500u/igt@kms_pipe_crc_basic@suspend-read-crc-pipe-a.html
>
> Please notice that the test we do in the CI involves putting the
> machine to sleep (PM), and the issue triggers when resuming execution.
>
> I have not been able to get my hands on the machine yet to do an actual
> bisect, but I'm wondering if you guys might have an idea of what is
> wrong.
>
> Any help is appreciated :)

Hi Gabriel,

This appears to be new behavior in blk-mq's tag set update with commit
705cda97e. This is asserting a lock is held, but none of the drivers
that call the export are take that lock.

I think the below should fix it (CC'ing block list and developers).
---
 block/blk-mq.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index a69ad122ed66..97fe71a17a27 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2660,7 +2660,8 @@ int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr)
 	return ret;
 }
 
-void blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, int nr_hw_queues)
+static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set,
+							int nr_hw_queues)
 {
 	struct request_queue *q;
 
@@ -2684,6 +2685,13 @@ void blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, int nr_hw_queues)
 	list_for_each_entry(q, &set->tag_list, tag_set_list)
 		blk_mq_unfreeze_queue(q);
 }
+
+void blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, int nr_hw_queues)
+{
+	mutex_lock(&set->tag_list_lock);
+	__blk_mq_update_nr_hw_queues(set, nr_hw_queues);
+	mutex_unlock(&set->tag_list_lock);
+}
 EXPORT_SYMBOL_GPL(blk_mq_update_nr_hw_queues);
 
 /* Enable polling stats and return whether they were already enabled. */
-- 
2.11.0