Re: Spurious EIO on AIO+DIO+RWF_NOWAIT

[Avi Kivity]

On 12/10/18 2:48 PM, Goldwyn Rodrigues wrote:
> On 13:19 09/12, Avi Kivity wrote:
> > I have an application that receives spurious EIO when running with
> > RWF_NOWAIT enabled. Removing RWF_NOWAIT causes those EIOs to disappear. The
> > application uses AIO+DIO, and errors were seen on both xfs and ext4.
> >
> >
> > I suspect the following code:
> >
> >
> > /*
> >  Â* Process one completed BIO. No locks are held.
> >  Â*/
> > static blk_status_t dio_bio_complete(struct dio *dio, struct bio *bio)
> > {
> >  ÂÂÂÂÂÂÂ struct bio_vec *bvec;
> >  ÂÂÂÂÂÂÂ unsigned i;
> >  ÂÂÂÂÂÂÂ blk_status_t err = bio->bi_status;
> >
> >  ÂÂÂÂÂÂÂ if (err) {
> >  ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ if (err == BLK_STS_AGAIN && (bio->bi_opf & REQ_NOWAIT))
> >  ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ dio->io_error = -EAGAIN;
> >  ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ else
> >  ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ dio->io_error = -EIO;
> >  ÂÂÂÂÂÂÂ }
> >
> > Could it be that REQ_NOWAIT was dropped from bio->bi_opf? or that
> > bio->bi_status got changed along the way?
> I don't think REQ_NOWAIT is dropped. I am assuming bio->bi_status error
> is set differently. Is the blk queue being stopped? Is it possible to
> instrument the kernel in your testcase?

I traced the function, and I see bio->bi_status == BLK_STS_NOTSUPP and 
bio->bi_opf == REQ_OP_WRITE|REQ_SYNC|REQ_NOMERGE|REQ_FUA|REQ_NOWAIT. 
Presumably the NOTSUPP is the result of NOWAIT not being supported down 
the stack, but shouldn't it be detected earlier? And not converted to EIO?