On 08/13/2019 08:13 AM, Josef Bacik wrote: > On Fri, Aug 09, 2019 at 04:26:10PM -0500, Mike Christie wrote: >> This fixes a regression added in 4.9 with commit: >> >> commit 0eadf37afc2500e1162c9040ec26a705b9af8d47 >> Author: Josef Bacik <jbacik@xxxxxx> >> Date: Thu Sep 8 12:33:40 2016 -0700 >> >> nbd: allow block mq to deal with timeouts >> >> where before the patch userspace would set the timeout to 0 to disable >> it. With the above patch, a zero timeout tells the block layer to use >> the default value of 30 seconds. For setups where commands can take a >> long time or experience transient issues like network disruptions this >> then results in IO errors being sent to the application. >> >> To fix this, the patch still uses the common block layer timeout >> framework, but if zero is set, nbd just logs a message and then resets >> the timer when it expires. >> >> Josef, >> >> I did not cc stable, but I think we want to port the patches to some >> releases. We originally hit this with users using the longterm kernels >> with ceph. The patch does not apply anywhere cleanly with older ones >> like 4.9, so I was not sure how we wanted to handle it. >> > > I assume you tested this? IIRC there was a problem where 0 really meant 0 and Yes. > commands would insta-timeout. But my memory is foggy here, so I'm not sure if > it was setting the tag_set timeout to 0 that made things go wrong, or what. Or > I could be making it all up, who knows. Yes, if you call blk_queue_rq_timeout with 0, then the command will timeout almost immediately. I added a check for this in the first patch. If blk_mq_tag_set.timeout is 0, blk_mq_init_allocated_queue uses the default 30 second value. So with the patch if the user sets the timeout to 0, then we will just log a message every 30 seconds that the command is stuck. > > There's a blktest that just runs fio on a normal device with no timeouts or > anything, that's where I would see the problem since it was a little racy. > Basically have the timeout set to 0 and put load on the disk and eventually > you'd start seeing timeouts. If that all goes fine then you can add > > Reviewed-by: Josef Bacik <josef@xxxxxxxxxxxxxx> > Ok.
