On 2017-11-13 16:00, Fam Zheng wrote:
> In the "Overlapping multiple requests" cases, the 3rd reqs (the break
> point B) doesn't wait for the 2nd, and once resumed the I/O will just
> continue. This is because the 2nd is already waiting for the 1st, and
> in wait_serialising_requests() there is:
>
> /* If the request is already (indirectly) waiting for us, or
> * will wait for us as soon as it wakes up, then just go on
> * (instead of producing a deadlock in the former case). */
> if (!req->waiting_for) {
> /* actually break */
> ...
> }
>
> Consequently, the following "sleep 100; resume A" command races with the
> completion of that request, and sometimes results in an unexpected
> order of output:
>
>> @@ -56,9 +56,9 @@
>> wrote XXX/XXX bytes at offset XXX
>> XXX bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
>> blkdebug: Resuming request 'B'
>> +blkdebug: Resuming request 'A'
>> wrote XXX/XXX bytes at offset XXX
>> XXX bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
>> -blkdebug: Resuming request 'A'
>> wrote XXX/XXX bytes at offset XXX
>> XXX bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
>> wrote XXX/XXX bytes at offset XXX
>
> Filter out the "Resuming request" lines to make the output
> deterministic.
>
> Reported-by: Patchew <[email protected]>
> Signed-off-by: Fam Zheng <[email protected]>
> ---
> tests/qemu-iotests/077 | 3 ++-
> tests/qemu-iotests/077.out | 48
> ++++++++++++++++------------------------------
> 2 files changed, 18 insertions(+), 33 deletions(-)Thanks, applied to my block tree: https://github.com/XanClic/qemu/commits/block Max
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