[PATCH] block: Fix blk_sync_queue() to properly stop timeout timer

[Mohamed Khalfella]

On 2025-05-29 16:13:23 -0600, Keith Busch wrote:
> On Thu, May 29, 2025 at 03:49:28PM -0600, Mohamed Khalfella wrote:
> > nvme-fc initiator hit hung_task with stacktrace above while handling
> > request timeout call. The work thread is waiting for itself to finish
> > which is never going to happen. From the stacktrace the nvme controller
> > was in NVME_CTRL_CONNECTING state when nvme_fc_timeout() was called.
> > We do not expect to get IO timeout call in NVME_CTRL_CONNECTING state
> > because blk_sync_queue() must have been called on this queue before
> > switching from NVME_CTRL_RESETTING to NVME_CTRL_CONNECTING.
> > 
> > It turned out that blk_sync_queue() did not stop q->timeout_work from
> > running as expected. nvme_fc_timeout() returned BLK_EH_RESET_TIMER
> > causing q->timeout to be rearmed after it was canceled earlier.
> > q->timeout queued q->timeout_work after the controller switched to
> > NVME_CTRL_CONNECTING state causing deadlock above.
> > 
> > Add QUEUE_FLAG_NOTIMEOUT queue flag to tell q->timeout not to queue
> > q->timeout_work while queue is being synced. Update blk_sync_queue() to
> > cancel q->timeout_work first and then cancel q->timeout.
> 
> I feel like this is a nvme-fc problem that doesn't need the block layer
> to handle. Just don't sync the queues within the timeout workqueue
> context.

Agreed on nvme-fc should not sync queues within timeout work, and I am
testing a patch to fix nvme-fc. At the same time blk_sync_queue() should
provide a guarantee that q->timeout_work will not run after the function
returns, no?