Re: BM_IO_ERROR flag is lost in TerminateBufferIO due to order of operations in UnlockBufHdrExt

27.03.2026 21:30, Yura Sokolov пишет:
> Good day,
>
> 27.03.2026 12:04, Yura Sokolov wrote:
>> 26.03.2026 23:29, Andres Freund wrote:
>>> Hi,
>>>
>>> On 2026-03-25 17:51:30 +0300, Yura Sokolov wrote:
>>>> UnlockBufHdrExt does:
>>>>
>>>> buf_state |= set_bits;
>>>> buf_state &= ~unset_bits;
>>>> buf_state &= ~BM_LOCKED;
>>>>
>>>> TerminateBufferIO unconditionally does:
>>>>
>>>> unset_flag_bits |= BM_IO_ERROR;
>>>>
>>>> Due to this, AbortBufferIO and buffer_readv_complete_one are failed
>>>> to set BM_IO_ERROR with call to TerminateBufferIO.
>>>>
>>>> It was found with proprietary code that was triggered on
>>>> PGAIO_RS_ERROR and made assertion on BM_IO_ERROR presence.
>>>
>>> That's clearly not right. Care to write a patch? I think we should add a
>>> test for this in src/test/modules/test_aio too. As we don't rely on things
>>> like BM_IO_ERROR this is quite easy to not notice.
>> I thought, fix is too small to go the way of patches.
>> I don't mind if you just push it.
>>
>> But if I can save your time on writing test, I'll try.
>>
>> ...
>>
>> I believe, proper way is to add assertion in UnlockBufHdrExt:
>>
>> Assert(!(set_bits & unset_bits));
>>
>> And make TerminateBufferIO to exclude BM_IO_ERROR if it is among
>> set_flag_bits.
>>
>> Is it ok?
>
> Here patchset is.
>
> I've tried to modify 001_aio.pl to test presence BM_IO_ERROR after read
> failure.
>
> I've also added FlushBuffer failure test in second patch (v1-002) using
> injection point. I don't know if 001-aio.pl is a good place for since write
> is not async yet.
>
> v1-003 just mades DebugPrintBufferRefcount prettier.

rebased.

--
regards
Yura Sokolov aka funny-falcon