Re: [BUG] ALSA: core: pcm_memory: a possible data race in do_alloc_pages()

[Jaroslav Kysela]

On 26. 06. 23 13:02, Takashi Iwai wrote:
> On Mon, 26 Jun 2023 09:56:47 +0200,
> Jaroslav Kysela wrote:
> > On 26. 06. 23 9:33, Takashi Iwai wrote:
> > > On Mon, 26 Jun 2023 09:31:18 +0200,
> > > Tuo Li wrote:
> > > > Hello,
> > > >
> > > > Thank you for your reply!
> > >
> > > FWIW, the simplest fix would be something like below, just extending
> > > the mutex coverage.  But it'll serialize the all calls, so it might
> > > influence on the performance, while it's the safest way.
> >
> > It may be better to update total_pcm_alloc_bytes before
> > snd_dma_alloc_dir_pages() call and decrease this value when allocation
> > fails to allow parallel allocations. Then the mutex can be held only
> > for the total_pcm_alloc_bytes variable update.
>
> Yes, it'd work.  But a tricky part is that the actual allocation size
> can be bigger, and we need to correct the total_pcm_alloc_bytes after
> the allocation result.  So the end result would be a patch like below,
> which is a bit more complex than the previous simpler approach.  But
> it might be OK.

The patch looks good, but it may be better to move the "post" variable updates 
to an inline function (mutex lock - update - mutex unlock) for a better 
readability.

					Jaroslav

--
Jaroslav Kysela <perex@xxxxxxxx>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.