Re: [PATCH] blk-mq: fix a hung issue when fsync

[Sasha Levin]

On Sun, Feb 17, 2019 at 04:37:29PM +0100, Thibaut Sautereau wrote:
> On Wed, Jan 30, 2019 at 08:54:09AM -0700, Jens Axboe wrote:
> > On 1/30/19 2:01 AM, Jianchao Wang wrote:
> > > Florian reported a io hung issue when fsync(). It should be
> > > triggered by following race condition.
> > >
> > > data + post flush         a flush
> > >
> > > blk_flush_complete_seq
> > >   case REQ_FSEQ_DATA
> > >     blk_flush_queue_rq
> > >     issued to driver      blk_mq_dispatch_rq_list
> > >                             try to issue a flush req
> > >                             failed due to NON-NCQ command
> > >                             .queue_rq return BLK_STS_DEV_RESOURCE
> > >
> > > request completion
> > >   req->end_io // doesn't check RESTART
> > >   mq_flush_data_end_io
> > >     case REQ_FSEQ_POSTFLUSH
> > >       blk_kick_flush
> > >         do nothing because previous flush
> > >         has not been completed
> > >      blk_mq_run_hw_queue
> > >                               insert rq to hctx->dispatch
> > >                               due to RESTART is still set, do nothing
> > >
> > > To fix this, replace the blk_mq_run_hw_queue in mq_flush_data_end_io
> > > with blk_mq_sched_restart to check and clear the RESTART flag.
> >
> > Applied, thanks.
> >
> > --
> > Jens Axboe
>
> Can this be applied to stable kernels please?
>
> It's commit 85bd6e61f34dffa8ec2dc75ff3c02ee7b2f1cbce upstream.

I've queued it for 4.20, 4.19 and 4.14.

--
Thanks,
Sasha