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Date: Wed, 12 Dec 2018 14:05:40 +0200
From: Avi Kivity <avi@...lladb.com>
To: Goldwyn Rodrigues <rgoldwyn@...e.de>
Cc: linux-kernel <linux-kernel@...r.kernel.org>, linux-aio@...ck.org
Subject: Re: Spurious EIO on AIO+DIO+RWF_NOWAIT
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?
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