Re: [REGRESSION] v5.17-rc1+: FIFREEZE ioctl system call hangs

[Song Liu <song@kernel.org>]

On Thu, Aug 25, 2022 at 12:12 PM Jens Axboe <axboe@kernel.dk> wrote:
>
> On 8/25/22 10:47 AM, Song Liu wrote:
> > On Tue, Aug 23, 2022 at 10:13 AM Song Liu <song@kernel.org> wrote:
> >>
> >> On Mon, Aug 22, 2022 at 8:15 PM Thomas Deutschmann <whissi@whissi.de> wrote:
> >>>
> >>> On 2022-08-23 03:37, Song Liu wrote:
> >>>> Thomas, have you tried to bisect with the fio repro?
> >>>
> >>> Yes, just finished:
> >>>
> >>>> d32d3d0b47f7e34560ae3c55ddfcf68694813501 is the first bad commit
> >>>> commit d32d3d0b47f7e34560ae3c55ddfcf68694813501
> >>>> Author: Christoph Hellwig
> >>>> Date:   Mon Jun 14 13:17:34 2021 +0200
> >>>>
> >>>>     nvme-multipath: set QUEUE_FLAG_NOWAIT
> >>>>
> >>>>     The nvme multipathing code just dispatches bios to one of the blk-mq
> >>>>     based paths and never blocks on its own, so set QUEUE_FLAG_NOWAIT
> >>>>     to support REQ_NOWAIT bios.
> >>>
> >>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=d32d3d0b47f7e34560ae3c55ddfcf68694813501
> >>>
> >>>
> >>> So another NOWAIT issue -- similar to the bad commit which is causing
> >>> the mdraid issue I already found
> >>> (https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=0f9650bd838efe5c52f7e5f40c3204ad59f1964d).
> >>>
> >>> Reverting the commit, i.e. deleting
> >>>
> >>>    blk_queue_flag_set(QUEUE_FLAG_NOWAIT, head->disk->queue);
> >>>
> >>> fixes the problem for me. Well, sort of. Looks like this will disable
> >>> io_uring. fio reproducer fails with
> >>
> >> My system doesn't have multipath enabled. I guess bisect will point to something
> >> else here.
> >>
> >> I am afraid we won't get more information from bisect.
> >
> > OK, I am able to pinpoint the issue, and Jens found the proper fix for
> > it (see below,
> > also available in [1]). It survived 100 runs of the repro fio job.
> >
> > Thomas, please give it a try.
> >
> > Thanks,
> > Song
> >
> > diff --git c/fs/io_uring.c w/fs/io_uring.c
> > index 3f8a79a4affa..72a39f5ec5a5 100644
> > --- c/fs/io_uring.c
> > +++ w/fs/io_uring.c
> > @@ -4551,7 +4551,12 @@ static int io_write(struct io_kiocb *req,
> > unsigned int issue_flags)
> >  copy_iov:
> >                 iov_iter_restore(&s->iter, &s->iter_state);
> >                 ret = io_setup_async_rw(req, iovec, s, false);
> > -               return ret ?: -EAGAIN;
> > +               if (!ret) {
> > +                       if (kiocb->ki_flags & IOCB_WRITE)
> > +                               kiocb_end_write(req);
> > +                       return -EAGAIN;
> > +               }
> > +               return 0;
>
> This should be 'return ret;' for that last line. I had to double check
> the ones I did, but they did get it right. But I did a double take when
> I saw this one :-)

Ah, right... "ret ?: -EAGAIN" is a lot of information..

Song

>
> It'll work fine for testing as we won't hit errors here unless we run
> out of memory, so...
>
> --
> Jens Axboe