Re: [PATCH] locking/locktorture: reject zero resolved worker threads

[Paul E. McKenney]

On Fri, Jun 05, 2026 at 06:47:05PM +0000, Samuel Moelius wrote:
> locktorture checks for a zero-worker configuration before it resolves
> the default reader count.  For reader-capable lock types, a user can
> pass nwriters_stress=0 and leave nreaders_stress at its default -1.
> This bypasses the early check, then derives the default real reader
> count from the real writer count, leaving both resolved counts at zero.
> 
> The module can then load successfully, optionally creating helper
> threads such as the stats thread, but no lock-torture worker threads.
> 
> Reject the resolved zero-worker state after reader defaults have been
> applied.
> 
> Assisted-by: Codex:gpt-5.5-cyber-preview
> Signed-off-by: Samuel Moelius <sam.moelius@xxxxxxxxxxxxxxx>
> ---
>  kernel/locking/locktorture.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/kernel/locking/locktorture.c b/kernel/locking/locktorture.c
> index e618bcf75e2d..7d553ecd3fab 100644
> --- a/kernel/locking/locktorture.c
> +++ b/kernel/locking/locktorture.c
> @@ -1320,6 +1320,13 @@ static int __init lock_torture_init(void)
>  			cxt.nrealreaders_stress = cxt.nrealwriters_stress;
>  		}
>  
> +		if (cxt.nrealwriters_stress == 0 &&
> +		    cxt.nrealreaders_stress == 0) {
> +			pr_alert("lock-torture: must run at least one locking thread\n");
> +			firsterr = -EINVAL;
> +			goto unwind;
> +		}
> +
>  		if (nreaders_stress) {
>  			cxt.lrsa = kmalloc_objs(*cxt.lrsa,
>  						cxt.nrealreaders_stress);

Fair point!

Though if we are to fully handle erroneous combinations of module
parameters to this debug module, there is also later code that updates
cxt.nrealwriters_stress *after* having allocated and initialized the
cxt.lwsa array.  And likely other issues.

Would you be willing to review lock_torture_init() to fix all aspects of
its error handling?  If we do it one at a time, we will after all likely
go in circles for some time.  And that won't be fun for any of us.  ;-)

							Thanx, Paul