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

[Haakon Bugge]

> On 13 Jul 2026, at 18:37, 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>

A gentle ping on this v2 of the series.


Thxs, Håkon

> 
> ---
> 
> v1 -> v2:
>      * Reworded commit message
> ---
> kernel/locking/test-ww_mutex.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/locking/test-ww_mutex.c b/kernel/locking/test-ww_mutex.c
> index 190b8ac5c5520..e97f7d94ca5ef 100644
> --- a/kernel/locking/test-ww_mutex.c
> +++ b/kernel/locking/test-ww_mutex.c
> @@ -457,6 +457,7 @@ static void stress_inorder_work(struct work_struct *work)
> 	struct ww_acquire_ctx ctx;
> 	int *order;
> 	int err;
> +	int attempts_after_tmout = 10000;
> 
> 	stress->result = -ENOMEM;
> 
> @@ -489,7 +490,7 @@ static void stress_inorder_work(struct work_struct *work)
> 			ww_mutex_unlock(&locks[order[n]]);
> 
> 		if (err == -EDEADLK) {
> -			if (!time_after(jiffies, stress->timeout)) {
> +			if ((!time_after(jiffies, stress->timeout)) || attempts_after_tmout--) {
> 				ww_mutex_lock_slow(&locks[order[contended]], &ctx);
> 				goto retry;
> 			}
> --
> 2.43.5