On Mon, Aug 02, 2021 at 02:40:36PM +0200, Kevin Wolf wrote:
> Am 29.07.2021 um 11:10 hat Fabian Ebner geschrieben:
> > Linux SCSI can throw spurious -EAGAIN in some corner cases in its
> > completion path, which will end up being the result in the completed
> > io_uring request.
> >
> > Resubmitting such requests should allow block jobs to complete, even
> > if such spurious errors are encountered.
> >
> > Co-authored-by: Stefan Hajnoczi <stefanha@gmail.com>
> > Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
> > Signed-off-by: Fabian Ebner <f.ebner@proxmox.com>
> > ---
> >
> > Changes from v1:
> > * Focus on what's relevant for the patch itself in the commit
> > message.
> > * Add Stefan's comment.
> > * Add Stefano's R-b tag (I hope that's fine, since there was no
> > change code-wise).
> >
> > block/io_uring.c | 16 +++++++++++++++-
> > 1 file changed, 15 insertions(+), 1 deletion(-)
> >
> > diff --git a/block/io_uring.c b/block/io_uring.c
> > index 00a3ee9fb8..dfa475cc87 100644
> > --- a/block/io_uring.c
> > +++ b/block/io_uring.c
> > @@ -165,7 +165,21 @@ static void luring_process_completions(LuringState *s)
> > total_bytes = ret + luringcb->total_read;
> >
> > if (ret < 0) {
> > - if (ret == -EINTR) {
> > + /*
> > + * Only writev/readv/fsync requests on regular files or host
block
> > + * devices are submitted. Therefore -EAGAIN is not expected
but it's
> > + * known to happen sometimes with Linux SCSI. Submit again and
hope
> > + * the request completes successfully.
> > + *
> > + * For more information, see:
> > + *
https://lore.kernel.org/io-uring/20210727165811.284510-3-axboe@kernel.dk/T/#u
> > + *
> > + * If the code is changed to submit other types of requests in
the
> > + * future, then this workaround may need to be extended to
deal with
> > + * genuine -EAGAIN results that should not be resubmitted
> > + * immediately.
> > + */
> > + if (ret == -EINTR || ret == -EAGAIN) {
> > luring_resubmit(s, luringcb);
> > continue;
> > }
>
> Reviewed-by: Kevin Wolf <kwolf@redhat.com>
>
> Question about the preexisting code, though: luring_resubmit() requires
> that the caller calls ioq_submit() later so that the request doesn't
> just sit in a queue without getting any attention, but actually gets
> submitted to the kernel.
>
> In the call chain ioq_submit() -> luring_process_completions() ->
> luring_resubmit(), who takes care of that?
Mmm, good point.
There should be the same problem with ioq_submit() ->
luring_process_completions() -> luring_resubmit_short_read() ->
luring_resubmit().
Should we schedule a BH for example in luring_resubmit() to make sure that
ioq_submit() is invoked after a resubmission?