On Wed, 23 Mar 2022 09:15:19 +0100,
Takashi Iwai wrote:
>
> On Wed, 23 Mar 2022 09:08:25 +0100,
> Amadeusz SX2awiX4ski wrote:
> >
> > On 3/22/2022 6:07 PM, Takashi Iwai wrote:
> > > Like the previous fixes to hw_params and hw_free ioctl races, we need
> > > to paper over the concurrent prepare ioctl calls against hw_params and
> > > hw_free, too.
> > >
> > > This patch implements the locking with the existing
> > > runtime->buffer_mutex for prepare ioctls. Unlike the previous case
> > > for snd_pcm_hw_hw_params() and snd_pcm_hw_free(), snd_pcm_prepare() is
> > > performed to the linked streams, hence the lock can't be applied
> > > simply on the top. For tracking the lock in each linked substream, we
> > > modify snd_pcm_action_group() slightly and apply the buffer_mutex for
> > > the case stream_lock=false (formerly there was no lock applied)
> > > there.
> > >
> > > Cc: <stable@xxxxxxxxxxxxxxx>
> > > Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
> > > ---
> > > sound/core/pcm_native.c | 32 ++++++++++++++++++--------------
> > > 1 file changed, 18 insertions(+), 14 deletions(-)
> > >
> > > diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
> > > index 266895374b83..0e4fbf5fd87b 100644
> > > --- a/sound/core/pcm_native.c
> > > +++ b/sound/core/pcm_native.c
> > > @@ -1190,15 +1190,17 @@ struct action_ops {
> > > static int snd_pcm_action_group(const struct action_ops *ops,
> > > struct snd_pcm_substream *substream,
> > > snd_pcm_state_t state,
> > > - bool do_lock)
> > > + bool stream_lock)
> > > {
> > > struct snd_pcm_substream *s = NULL;
> > > struct snd_pcm_substream *s1;
> > > int res = 0, depth = 1;
> > > snd_pcm_group_for_each_entry(s, substream) {
> > > - if (do_lock && s != substream) {
> > > - if (s->pcm->nonatomic)
> > > + if (s != substream) {
> > > + if (!stream_lock)
> > > + mutex_lock_nested(&s->runtime->buffer_mutex, depth);
> > > + else if (s->pcm->nonatomic)
> > > mutex_lock_nested(&s->self_group.mutex, depth);
> > > else
> > > spin_lock_nested(&s->self_group.lock, depth);
> >
> > Maybe
> > if (!stream_lock)
> > mutex_lock_nested(&s->runtime->buffer_mutex, depth);
> > else
> > snd_pcm_group_lock(&s->self_group, s->pcm->nonatomic);
> > ?
>
> No, it must be nested locks with the given subclass.
FWIW, the reason is that lockdep would complain otherwise as if it
were a deadlock. That is, this is a workaround for avoiding false
lockdep warnings.
Takashi
