Re: [PATCH] ALSA: timer: fix deadlock in _snd_pcm_stream_lock_irqsave

[Takashi Iwai]

On Thu, 21 Mar 2024 03:22:24 +0100,
Edward Adam Davis wrote:
> 
> [Syzbot reported]
> swapper/2/0 just changed the state of lock:
> ffff88802a304110 (&group->lock#2){..-.}-{2:2}, at: _snd_pcm_stream_lock_irqsave+0xa0/0xd0 sound/core/pcm_native.c:170
> but this lock took another, SOFTIRQ-unsafe lock in the past:
>  (&timer->lock){+.+.}-{2:2}
> 
> 
> and interrupts could create inverse lock ordering between them.
> 
> 
> other info that might help us debug this:
>  Possible interrupt unsafe locking scenario:
> 
>        CPU0                    CPU1
>        ----                    ----
>   lock(&timer->lock);
>                                local_irq_disable();
>                                lock(&group->lock#2);
>                                lock(&timer->lock);
>   <Interrupt>
>     lock(&group->lock#2);
> 
>  *** DEADLOCK ***
> [Fix]
> Ensure that the context interrupt state is the same before and after using the
> timer->lock.
> 
> Fixes: beb45974dd49 ("ALSA: timer: Use guard() for locking")
> Reported-and-tested-by: syzbot+18840ef96e57b83b7fea@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Edward Adam Davis <eadavis@xxxxxx>

This was already fixed in Linus tree commit
587d67fd929ad89801bcc429675bda90d53f6592.


thanks,

Takashi