Messages in this thread | | | Date | Wed, 12 Dec 2018 08:41:30 -0600 | From | Goldwyn Rodrigues <> | Subject | Re: Spurious EIO on AIO+DIO+RWF_NOWAIT |
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On 14:05 12/12, Avi Kivity wrote: > 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: > > > > > > > > > /* > > > * Process one completed BIO. No locks are held. > > > */ > > > static blk_status_t dio_bio_complete(struct dio *dio, struct bio *bio) > > > { > > > struct bio_vec *bvec; > > > unsigned i; > > > blk_status_t err = bio->bi_status; > > > > > > if (err) { > > > if (err == BLK_STS_AGAIN && (bio->bi_opf & REQ_NOWAIT)) > > > dio->io_error = -EAGAIN; > > > else > > > dio->io_error = -EIO; > > > } > > > > > > 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? >
I don't think there is a way to detect it earlier. However, I think we should return -EOPNOTSUPP if the lower layers do not support REQ_NOWAIT. I will write a patch to modify this.
-- Goldwyn
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