Re: [bug report] fstests generic/774 hang

[John Garry <john.g.garry@oracle.com>]

>>>>
>>>> Shinichiro, do the other atomic writes tests run ok, like 775, 767? You
>>>> can check group "atomicwrites" to know which tests they are.
>>>>
>>>> 774 is the fio test.
> 
> I tried the other "atomicwrites" test. I found g778 took very long time.
> I think it implies that g778 may have similar problem as g774.
> 
>    g765: [not run] write atomic not supported by this block device
>    g767: 11s
>    g768: 13s
>    g769: 13s
>    g770: 35s
>    g773: [not run] write atomic not supported by this block device
>    g774: did not completed after 3 hours run (and kernel reported the INFO messages)
>    g775: 48s
>    g776: [not run] write atomic not supported by this block device
>    g778: did not completed after 50 minutes run
>    x838: [not run] External volumes not in use, skipped this test
>    x839: [not run] XFS error injection requires CONFIG_XFS_DEBUG
>    x840: [not run] write atomic not supported by this block device

This is testing software-based atomic writes, and they are just slow. 
Very slow, relative to HW-based atomic writes. And having bs=1M will 
make things worse, as we are locking out other threads for longer (when 
doing the write). So I think that we should limit the file size which we 
try to write.

> 
>>>>
>>>> Some things to try:
>>>> - use a physical disk for the TEST_DEV
> 
> I tried using a real HDD for TEST_DEV, but still observed the hang and INFO
> messages at g774.
> 
>>>> - Don't set LOAD_FACTOR (if you were setting it). If not, bodge 774 to
>>>> reduce $threads to a low value, say, 2
> 
> I do not set LOAD_FACTOR. I changed g775 script to set threads=2, then the
> test case completed quickly, within a few minutes. I'm suspecting that this
> short test time might hide the hang/INFO problem.
> 
>>>> - trying turning on XFS_DEBUG config
> 
> I turned on XFS_DEBUG, and still observed the hang and the INFO messages.
> 

I don't think that this will help.

>>>>
>>>> BTW, Darrick has posted some xfs atomics fixes @ https://urldefense.com/
>>>> v3/__https://urldefense.com/v3/__https://lore.kernel.org/linux-__;!!ACWV5N9M2RV99hQ!J3HKTWLF8Qx-j42OOJ4o1YAttSSoqOCm9ymJtisUYoOtGgOyNNGqHnjjl1Zd9DQXJvCz8zqPMG-kgeVdo9MQuupMlcAo$
>>>> xfs/20251105001200.GV196370@frogsfrogsfrogs/T/*t__;Iw!!ACWV5N9M2RV99hQ! IuEPY6yJ1ZEQu7dpfjUplkPJucOHMQ9cpPvIC4fiJhTi_X_7ImN0t6wGqxg9_GM6gWe4B1OBiBjEI8Gz_At0595tIQ$
>>>> . I doubt that they will help this, but worth trying.
> 
> I have not yet tried this. Will try it tomorrow.

Nor this.

Having a hang - even for the conditions set - should not produce a hang. 
I can check on whether we can improve the software-based atomic writes 
in xfs to avoid this.

Thanks,
John