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Subject: Re: Spurious EIO on AIO+DIO+RWF_NOWAIT
To:     Goldwyn Rodrigues <rgoldwyn@suse.de>
Cc:     linux-kernel <linux-kernel@vger.kernel.org>, linux-aio@kvack.org
References: <9bab0f40-5748-f147-efeb-5aac4fd44533@scylladb.com>
 <20181210124823.iw4mxmdqpsdfeap4@merlin>
From:   Avi Kivity <avi@scylladb.com>
Organization: ScyllaDB
Message-ID: <53c17661-4914-5266-2034-9fc447e59383@scylladb.com>
Date:   Mon, 10 Dec 2018 14:49:44 +0200
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On 10/12/2018 14.48, 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?


Not that I know of.


> Is it possible to
> instrument the kernel in your testcase?
>

I'm happy to apply patches, or run systemtap (or similar) scripts.