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

[Song Liu <song@kernel.org>]

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;
        }
 out_free:
        /* it's reportedly faster than delegating the null check to kfree() */

[1] https://lore.kernel.org/stable/a603cfc5-9ba5-20c3-3fec-2c4eec4350f7@kernel.dk/T/#u