Re: xfs: log recovery hang fixes

[Matthew Wilcox <willy@infradead.org>]

On Mon, Mar 07, 2022 at 04:32:49PM +1100, Dave Chinner wrote:
> Willy reported generic/530 had started hanging on his test machines
> and I've tried to reproduce the problem he reported. While I haven't
> reproduced the exact hang he's been having, I've found a couple of
> others while running g/530 in a tight loop on a couple of test
> machines.
[...]
> 
> Willy, can you see if these patches fix the problem you are seeing?
> If not, I still think they stand alone as necessary fixes, but I'll
> have to keep digging to find out why you are seeing hangs in g/530.

I no longer see hangs, but I do see an interesting pattern in runtime
of g/530.  I was seeing hangs after only a few minutes of running g/530,
and I was using 15 minutes of success to say "git bisect good".  Now at 45
minutes of runtime with no hangs.  Specifically, I'm testing 0020a190cf3e
("xfs: AIL needs asynchronous CIL forcing"), plus these three patches.
If you're interested, I can see which of these three patches actually
fixes my hang.  I should also test these three patches on top of current
5.17-rc, but I wanted to check they were backportable to current stable
first.

Of the 120 times g/530 has run, I see 30 occurrences of the test taking
32-35 seconds.  I see one occurrence of the test taking 63 seconds.
Usually it takes 2-3s.  This smacks to me of a 30s timeout expiring.
Let me know if you want me to try to track down which one it is.