On Thu, May 18, 2017 at 10:13:07AM -0400, Keith Busch wrote: > On Wed, May 17, 2017 at 09:27:28AM +0800, Ming Lei wrote: > > When one NVMe PCI device is being resetted and found reset failue, > > nvme_remove_dead_ctrl() is called to handle the failure: blk-mq hw queues > > are put into stopped first, then schedule .remove_work to release the driver. > > > > Unfortunately if the driver is being released via sysfs store > > just before the .remove_work is run, del_gendisk() from > > nvme_remove() may hang forever because hw queues are stopped and > > the submitted writeback IOs from fsync_bdev() can't be completed at all. > > > > This patch fixes the following issue[1][2] by moving nvme_kill_queues() > > into nvme_remove_dead_ctrl() to avoid the issue because nvme_remove() > > flushs .reset_work, and this way is reasonable and safe because > > nvme_dev_disable() has started to suspend queues and canceled requests > > already. > > I'm still not sure moving where we kill the queues is the correct way > to fix this problem. The nvme_kill_queues restarts all the hardware > queues to force all IO to failure already, so why is this really stuck? That is a good question. Today I investigate further, and figured out that it is because that blk_mq_start_stopped_hw_queues() in nvme_kill_queues() does not run hw queues actually becasue the queues are started in nvme_reset_work() already. Will figure out a patch later to fix the issue. And the reason why this patch 'fixes' the issue is that just timing, I guess. > We should be able to make forward progress even if we kill the queues > while calling into del_gendisk, right? That could happen with a different > sequence of events, so that also needs to work. Now I am not a big fun of this patch for fixing the issue. But I still think it may be better to move nvme_kill_queues() into nvme_remove_dead_ctrl() as an improvement because during this small window page cache can be used up by write application, and no writeback can move on meantime. Thanks, Ming
