2022-03-23 08:14:31

by Takashi Iwai

Subject: [PATCH 3/4] ALSA: pcm: Fix races among concurrent prepare and hw_params/hw_free calls

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: <[email protected]>
Signed-off-by: Takashi Iwai <[email protected]>
---
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);
@@ -1226,18 +1228,18 @@ static int snd_pcm_action_group(const struct action_ops *ops,
ops->post_action(s, state);
}
_unlock:
- if (do_lock) {
- /* unlock streams */
- snd_pcm_group_for_each_entry(s1, substream) {
- if (s1 != substream) {
- if (s1->pcm->nonatomic)
- mutex_unlock(&s1->self_group.mutex);
- else
- spin_unlock(&s1->self_group.lock);
- }
- if (s1 == s) /* end */
- break;
+ /* unlock streams */
+ snd_pcm_group_for_each_entry(s1, substream) {
+ if (s1 != substream) {
+ if (!stream_lock)
+ mutex_unlock(&s1->runtime->buffer_mutex);
+ else if (s1->pcm->nonatomic)
+ mutex_unlock(&s1->self_group.mutex);
+ else
+ spin_unlock(&s1->self_group.lock);
}
+ if (s1 == s) /* end */
+ break;
}
return res;
}
@@ -1367,10 +1369,12 @@ static int snd_pcm_action_nonatomic(const struct action_ops *ops,

/* Guarantee the group members won't change during non-atomic action */
down_read(&snd_pcm_link_rwsem);
+ mutex_lock(&substream->runtime->buffer_mutex);
if (snd_pcm_stream_linked(substream))
res = snd_pcm_action_group(ops, substream, state, false);
else
res = snd_pcm_action_single(ops, substream, state);
+ mutex_unlock(&substream->runtime->buffer_mutex);
up_read(&snd_pcm_link_rwsem);
return res;
}
--
2.31.1

2022-03-23 14:20:10

by Amadeusz Sławiński

Subject: Re: [PATCH 3/4] ALSA: pcm: Fix races among concurrent prepare and hw_params/hw_free calls

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: <[email protected]>
> Signed-off-by: Takashi Iwai <[email protected]>
> ---
> 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);
?

> @@ -1226,18 +1228,18 @@ static int snd_pcm_action_group(const struct action_ops *ops,
> ops->post_action(s, state);
> }
> _unlock:
> - if (do_lock) {
> - /* unlock streams */
> - snd_pcm_group_for_each_entry(s1, substream) {
> - if (s1 != substream) {
> - if (s1->pcm->nonatomic)
> - mutex_unlock(&s1->self_group.mutex);
> - else
> - spin_unlock(&s1->self_group.lock);
> - }
> - if (s1 == s) /* end */
> - break;
> + /* unlock streams */
> + snd_pcm_group_for_each_entry(s1, substream) {
> + if (s1 != substream) {
> + if (!stream_lock)
> + mutex_unlock(&s1->runtime->buffer_mutex);
> + else if (s1->pcm->nonatomic)
> + mutex_unlock(&s1->self_group.mutex);
> + else
> + spin_unlock(&s1->self_group.lock);

And similarly to above, use snd_pcm_group_unlock() here?

> }
> + if (s1 == s) /* end */
> + break;
> }
> return res;
> }
> @@ -1367,10 +1369,12 @@ static int snd_pcm_action_nonatomic(const struct action_ops *ops,
>
> /* Guarantee the group members won't change during non-atomic action */
> down_read(&snd_pcm_link_rwsem);
> + mutex_lock(&substream->runtime->buffer_mutex);
> if (snd_pcm_stream_linked(substream))
> res = snd_pcm_action_group(ops, substream, state, false);
> else
> res = snd_pcm_action_single(ops, substream, state);
> + mutex_unlock(&substream->runtime->buffer_mutex);
> up_read(&snd_pcm_link_rwsem);
> return res;
> }

2022-03-24 18:17:40

by Takashi Iwai

Subject: Re: [PATCH 3/4] ALSA: pcm: Fix races among concurrent prepare and hw_params/hw_free calls

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: <[email protected]>
> > Signed-off-by: Takashi Iwai <[email protected]>
> > ---
> > 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. That's why it
has been the open code beforehand, too.

> > @@ -1226,18 +1228,18 @@ static int snd_pcm_action_group(const struct action_ops *ops,
> > ops->post_action(s, state);
> > }
> > _unlock:
> > - if (do_lock) {
> > - /* unlock streams */
> > - snd_pcm_group_for_each_entry(s1, substream) {
> > - if (s1 != substream) {
> > - if (s1->pcm->nonatomic)
> > - mutex_unlock(&s1->self_group.mutex);
> > - else
> > - spin_unlock(&s1->self_group.lock);
> > - }
> > - if (s1 == s) /* end */
> > - break;
> > + /* unlock streams */
> > + snd_pcm_group_for_each_entry(s1, substream) {
> > + if (s1 != substream) {
> > + if (!stream_lock)
> > + mutex_unlock(&s1->runtime->buffer_mutex);
> > + else if (s1->pcm->nonatomic)
> > + mutex_unlock(&s1->self_group.mutex);
> > + else
> > + spin_unlock(&s1->self_group.lock);
>
> And similarly to above, use snd_pcm_group_unlock() here?

This side would be possible to use that macro but it's still better to
have the consistent call pattern.


thanks,

Takashi

2022-03-25 17:57:57

by Takashi Iwai

Subject: Re: [PATCH 3/4] ALSA: pcm: Fix races among concurrent prepare and hw_params/hw_free calls

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: <[email protected]>
> > > Signed-off-by: Takashi Iwai <[email protected]>
> > > ---
> > > 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