Re: [PATCH 1/2] s390/dasd: Add __context_unsafe() attribute to various functions

[Heiko Carstens <hca@linux.ibm.com>]

On Thu, Aug 06, 2026 at 01:09:16PM +0000, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
...
> >  static int dasd_eckd_pe_handler(struct dasd_device *device,
> >  				__u8 tbvpm, __u8 fcsecpm)
> > +__context_unsafe(/* Conditional locking */)
> >  {
> >  	struct pe_handler_work_data *data;
> 
> [Severity: High]
> This is a pre-existing issue, but does silencing this warning hide a
> legitimate cross-thread mutex unlock?
> 
> When kzalloc fails in dasd_eckd_pe_handler(), it calls mutex_trylock(),
> establishing the current interrupted task as the lock owner:
> 
> dasd_eckd_pe_handler() {
>     ...
>     data = kzalloc_obj(*data, GFP_ATOMIC | GFP_DMA);
>     if (!data) {
>         if (mutex_trylock(&dasd_pe_handler_mutex)) {
>             data = pe_handler_worker;
>             data->isglobal = 1;
>     ...
>     schedule_work(&data->worker);
> }
> 
> The lock is then released from a different task (the workqueue worker thread)
> in do_pe_handler_work():
> 
> do_pe_handler_work() {
>     ...
>     if (data->isglobal)
>         mutex_unlock(&dasd_pe_handler_mutex);
>     ...
> }
> 
> Unlocking a struct mutex from a task other than the one that acquired it
> strictly violates mutex semantics, which could cause debug warnings or
> panics.
> 
> Additionally, mutex_trylock() in atomic context (inferred from GFP_ATOMIC
> usage) violates lockdep wait-context rules and PREEMPT_RT requirements.
> 
> Could this code be restructured to avoid the cross-thread unlock rather than
> silencing the warning?

This looks indeed like a valid finding. Looking at the code it looks to me
like there is no need for a mutex at all. Instead a simple integer which
indicates if the global pe_handler_work_data is used should be
sufficient. Exclusive access would then be tried to get with xchg().

Jens, Stefan, should this be addressed before or after this small series?
I would prefer after this series, since in the meantime I dislike those
"pre-existing" bugs, which pile up :)