Re: [bug report] fstests generic/774 hang again

[John Garry <john.garry@linux.dev>]

On 9/15/26 12:48, Shin'ichiro Kawasaki wrote:
> On Sep 15, 2026 / 11:00, John Garry wrote:
>> On 9/15/26 10:34, Shin'ichiro Kawasaki wrote:
>>> I observe the fstests test case generic/774 hangs, when I run it for xfs on 8GiB
>>> TCMU fileio devices. Actually I once reported this hang symptom in last October,
>>> and Darrick and John kindly took some actions [1]. Since then, the hang
>>> disappeared and I have not observed the hang almost one year. However, my test
>>> system started reporting the hang again last week.
>>>
>>> [1] https://lore.kernel.org/linux-xfs/cmk52aqexackyz65phxgme55a3tdrermo3o4skr4lo4pwvvvcp@jmcblnfikbp2/#t
>>
>> This was the series to resolve, I think:
>> https://lore.kernel.org/fstests/176279908967.605950.2192923313361120314.stgit@frogsfrogsfrogs/T/#t
>>
>> As an experiment, can you reduce the file size further, like:
>>
>> --- a/tests/generic/774
>> +++ b/tests/generic/774
>> @@ -29,7 +29,7 @@ aw_bsize=$(_max "$awu_min_write" "$((awu_max_write/4))")
>>   fsbsize=$(_get_block_size $SCRATCH_MNT)
>>
>>   threads=$(_min "$(($(nproc) * 2 * LOAD_FACTOR))" "100")
>> -filesize=$((aw_bsize * threads * 10))
>> +filesize=$((aw_bsize * threads))
>>   depth=$threads
>>   aw_io_size=$((filesize / threads))
>>   aw_io_inc=$aw_io_size
> 
> Thanks for the response. I repeated the test case 100 times with the change
> above, and I did not observe the hang. The change looks avoiding the hang.
> 
>>
>>>
>>> FYI, here I attache the kernel message [2].
>>
>> Is mainline baseline hanging, i.e. v7.3-rc2?
> 
> I will try this out tomorrow.

thanks

About the kernel code, I am wondering if using IOMAP_DIO_FORCE_WAIT for 
CoW-based atomics could help avoid this issue as we seem to be bogged 
down in lock contention.