Re: [PATCH v4] s390/pai: Handle multiple PMU stop callback invocations

On Wed, Aug 19, 2026 at 07:58:55AM +0200, Thomas Richter wrote:
> Handle the following scenario:
> The kernel protects itself against a very high sampling load and
> throttles the sampling using:
> 
>   perf_event_throttle() --> PMU->stop()
> 
> Shortly later the scheduler may terminate the task and removes it from the
> CPU. It again calls
> 
>   PMU->stop()
> 
> which results in two invocations of PMU->stop() called back to back.
> Protect against this and check the PERF_HES_STOPPED bit on function
> entry.  If it is already set return.
> Clear bit PERF_HES_STOPPED in PMU->start().
> 
> Prohibit ioctl(fd, PERF_EVENT_IOC_PERIOD, ...) call for this event.
> It sets perf_event::event_limit to a positive value and causes
> perf_event_overflow() to invoke pai_stop() call back function when
> perf_event::event_limit hits zero. This is not supported because the
> sample events CRYPTO_ALL and NNPA_ALL are only taken at schedule out
> of a task.
> 
> Use list_for_each_entry_safe() for safe iteration over syswide_list
> in pai_have_samples().
> 
>  #Cc: [email protected] # v6.19+
> Fixes: 9f66572f2889 ("s390/pai_crypto: Enable per-task and system-wide sampling event")
> Fixes: 582cc1b28e8c ("s390/pai_ext: Enable per-task and system-wide sampling event")
> Signed-off-by: Thomas Richter <[email protected]>
> Reviewed-by: Sumanth Korikkar <[email protected]>
> Suggested-by: Heiko Carstens <[email protected]>
> ---
>  arch/s390/kernel/perf_pai.c | 25 +++++++++++++++++++++++--
>  1 file changed, 23 insertions(+), 2 deletions(-)

Applied, thank you!