Re: [PATCH v2 4/4] test-ww_mutex: Retry lock acquisition after timeout if deadlocked

[John Stultz]

On Mon, Jul 13, 2026 at 9:37 AM Håkon Bugge <haakon.bugge@xxxxxxxxxx> wrote:
>
> stress_inorder_work() terminates when its timeout expires. If the
> final lock acquisition attempt returns -EDEADLK at that point, the
> test may report a false failure.
>
> With a high number of threads and few locks, there is a very high
> probability that a thread will be subject to lock contention. That
> implies, when the loop times out, we will most probably have been
> exposed to a -EDEADLK return.
>
> Therefore, we retry a finite number of times after timeout before
> reporting failure.
>
> We retry up to 10,000 loops after timeout. This value was determined
> empirically: 10 and 100 retries were insufficient on the test systems,
> while 10,000 provided stable results and avoided false negatives.
>
> Without this commit, we may see in the log:
>
>    Beginning ww (wound) mutex selftests
>    stress (stress_inorder_work) failed with -35
>
> Fixes: cfa92b6d5207 ("locking/ww_mutex/test: Make sure we bail out instead of livelock")
> Signed-off-by: Håkon Bugge <haakon.bugge@xxxxxxxxxx>

So I've utilized this in my testing with proxy-exec v31 and have not
seen any practical troubles with it.

However, I still am not very happy with the post-timeout retrys,
particularly as it is such a high retry value.

It still feels like we're papering over a problem we don't understand
well, and it might be better to leave it failing until we can better
articulate what's going on and why this is the right solution.

The rest of the patchset looks great, but I'd maybe drop this one from
the series for now.

thanks
-john