On Mon, 19 Jul 2021 09:54:52 +0200, Daniel Bristot de Oliveira wrote:
> eventfd_signal assumes that spin_lock_irqsave/spin_unlock_irqrestore is
> non-preemptable and therefore increments and decrements the percpu
> variable inside the critical section.
>
> This obviously does not fly with PREEMPT_RT. If eventfd_signal is
> preempted and an unrelated thread calls eventfd_signal, the result is
> a spurious WARN. To avoid this, protect the percpu variable with a
> local_lock.
>
> Reported-by: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
> Fixes: b5e683d5cab8 ("eventfd: track eventfd_signal() recursion depth")
> Cc: He Zhe <zhe.he@xxxxxxxxxxxxx>
> Cc: Jens Axboe <axboe@xxxxxxxxx>
> Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Cc: linux-fsdevel@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Co-developed-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Signed-off-by: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
> ---
Tested-by: Nicolas Saenz Julienne <nsaenzju@xxxxxxxxxx>
Thanks!
--
Nicolás Sáenz
