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SubjectRe: [PATCH 5.4 103/142] Revert "block: end bio with BLK_STS_AGAIN in case of non-mq devs and REQ_NOWAIT"
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On 2/3/21 3:06 PM, Greg Kroah-Hartman wrote:
> On Wed, Feb 03, 2021 at 01:28:26PM -0800, Andres Freund wrote:
>> Hi,
>>
>> On 2021-02-03 14:03:09 +0100, Greg Kroah-Hartman wrote:
>>>> On v5.4.43-101-gbba91cdba612 this fails with
>>>> fio: io_u error on file /mnt/t2/test.0.0: Input/output error: write offset=0, buflen=4096
>>>> fio: pid=734, err=5/file:io_u.c:1834, func=io_u error, error=Input/output error
>>>>
>>>> whereas previously it worked. libaio still works...
>>>>
>>>> I haven't checked which major kernel version fixed this again, but I did
>>>> verify that it's still broken in 5.4.94 and that 5.10.9 works.
>>>>
>>>> I would suspect it's
>>>>
>>>> commit 4503b7676a2e0abe69c2f2c0d8b03aec53f2f048
>>>> Author: Jens Axboe <axboe@kernel.dk>
>>>> Date: 2020-06-01 10:00:27 -0600
>>>>
>>>> io_uring: catch -EIO from buffered issue request failure
>>>>
>>>> -EIO bubbles up like -EAGAIN if we fail to allocate a request at the
>>>> lower level. Play it safe and treat it like -EAGAIN in terms of sync
>>>> retry, to avoid passing back an errant -EIO.
>>>>
>>>> Catch some of these early for block based file, as non-mq devices
>>>> generally do not support NOWAIT. That saves us some overhead by
>>>> not first trying, then retrying from async context. We can go straight
>>>> to async punt instead.
>>>>
>>>> Signed-off-by: Jens Axboe <axboe@kernel.dk>
>>>>
>>>>
>>>> which isn't in stable/linux-5.4.y
>>>
>>> Can you test that if the above commit is added, all works well again?
>>
>> It doesn't apply cleanly, I'll try to resolve the conflict. However, I
>> assume that the revert was for a concrete reason - but I can't quite
>> figure out what b0beb28097fa04177b3769f4bb7a0d0d9c4ae76e was concretely
>> solving, and whether reverting the revert in 5.4 would re-introduce a
>> different problem.
>>
>> commit b0beb28097fa04177b3769f4bb7a0d0d9c4ae76e (tag: block-5.7-2020-05-29, linux-block/block-5.7)
>> Author: Jens Axboe <axboe@kernel.dk>
>> Date: 2020-05-28 13:19:29 -0600
>>
>> Revert "block: end bio with BLK_STS_AGAIN in case of non-mq devs and REQ_NOWAIT"
>>
>> This reverts commit c58c1f83436b501d45d4050fd1296d71a9760bcb.
>>
>> io_uring does do the right thing for this case, and we're still returning
>> -EAGAIN to userspace for the cases we don't support. Revert this change
>> to avoid doing endless spins of resubmits.
>>
>> Cc: stable@vger.kernel.org # v5.6
>> Reported-by: Bijan Mottahedeh <bijan.mottahedeh@oracle.com>
>> Signed-off-by: Jens Axboe <axboe@kernel.dk>
>>
>> I suspect it just wasn't aimed at 5.4, and that's that, but I'm not
>> sure. In which case presumably reverting
>> bba91cdba612fbce4f8575c5d94d2b146fb83ea3 would be the right fix, not
>> backporting 4503b7676a2e0abe69c2f2c0d8b03aec53f2f048 et al.
>
> Ok, can you send a revert patch for this?
>
> But it would be good to get Jens to weigh in on this...

I'll take a look at this.

--
Jens Axboe

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