* [PATCH 0/2] ALSA: pcm: stream linking locking fixes
@ 2020-06-08 10:06 Michał Mirosław
2020-06-08 10:06 ` [PATCH 2/2] ALSA: pcm: fix snd_pcm_link() lockdep splat Michał Mirosław
2020-06-08 10:06 ` [PATCH 1/2] ALSA: pcm: disallow linking stream to itself Michał Mirosław
0 siblings, 2 replies; 7+ messages in thread
From: Michał Mirosław @ 2020-06-08 10:06 UTC (permalink / raw)
To: Jaroslav Kysela, Takashi Iwai; +Cc: alsa-devel, linux-kernel
Two patches fixing locking issues for SNDRV_PCM_IOCTL_LINK handling:
first adds a check preventing linking a stream to itself, second quiets
lockdep warning about nested locks.
Michał Mirosław (2):
ALSA: pcm: disallow linking stream to itself
ALSA: pcm: fix snd_pcm_link() lockdep splat
sound/core/pcm_native.c | 20 ++++++++++++++++++--
1 file changed, 18 insertions(+), 2 deletions(-)
--
2.20.1
^ permalink raw reply [flat|nested] 7+ messages in thread
* [PATCH 1/2] ALSA: pcm: disallow linking stream to itself
2020-06-08 10:06 [PATCH 0/2] ALSA: pcm: stream linking locking fixes Michał Mirosław
2020-06-08 10:06 ` [PATCH 2/2] ALSA: pcm: fix snd_pcm_link() lockdep splat Michał Mirosław
@ 2020-06-08 10:06 ` Michał Mirosław
2020-06-08 12:48 ` Takashi Iwai
1 sibling, 1 reply; 7+ messages in thread
From: Michał Mirosław @ 2020-06-08 10:06 UTC (permalink / raw)
To: Jaroslav Kysela, Takashi Iwai; +Cc: alsa-devel, linux-kernel
Prevent SNDRV_PCM_IOCTL_LINK linking stream to itself - the code
can't handle it. Fixed commit is not where bug was introduced, but
changes the context significantly.
Cc: stable@vger.kernel.org
Fixes: 0888c321de70 ("pcm_native: switch to fdget()/fdput()")
Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
---
sound/core/pcm_native.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index aef860256278..3ad399cb6f30 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -2166,6 +2166,12 @@ static int snd_pcm_link(struct snd_pcm_substream *substream, int fd)
}
pcm_file = f.file->private_data;
substream1 = pcm_file->substream;
+
+ if (substream == substream1) {
+ res = -EDEADLK;
+ goto _badf;
+ }
+
group = kzalloc(sizeof(*group), GFP_KERNEL);
if (!group) {
res = -ENOMEM;
--
2.20.1
^ permalink raw reply related [flat|nested] 7+ messages in thread
* [PATCH 2/2] ALSA: pcm: fix snd_pcm_link() lockdep splat
2020-06-08 10:06 [PATCH 0/2] ALSA: pcm: stream linking locking fixes Michał Mirosław
@ 2020-06-08 10:06 ` Michał Mirosław
2020-06-08 13:02 ` Takashi Iwai
2020-06-08 10:06 ` [PATCH 1/2] ALSA: pcm: disallow linking stream to itself Michał Mirosław
1 sibling, 1 reply; 7+ messages in thread
From: Michał Mirosław @ 2020-06-08 10:06 UTC (permalink / raw)
To: Jaroslav Kysela, Takashi Iwai; +Cc: alsa-devel, linux-kernel
Add and use snd_pcm_stream_lock_nested() in snd_pcm_link/unlink
implementation. The code is fine, but generates a lockdep complaint:
============================================
WARNING: possible recursive locking detected
5.7.1mq+ #381 Tainted: G O
--------------------------------------------
pulseaudio/4180 is trying to acquire lock:
ffff888402d6f508 (&group->lock){-...}-{2:2}, at: snd_pcm_common_ioctl+0xda8/0xee0 [snd_pcm]
but task is already holding lock:
ffff8883f7a8cf18 (&group->lock){-...}-{2:2}, at: snd_pcm_common_ioctl+0xe4e/0xee0 [snd_pcm]
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0
----
lock(&group->lock);
lock(&group->lock);
*** DEADLOCK ***
May be due to missing lock nesting notation
2 locks held by pulseaudio/4180:
#0: ffffffffa1a05190 (snd_pcm_link_rwsem){++++}-{3:3}, at: snd_pcm_common_ioctl+0xca0/0xee0 [snd_pcm]
#1: ffff8883f7a8cf18 (&group->lock){-...}-{2:2}, at: snd_pcm_common_ioctl+0xe4e/0xee0 [snd_pcm]
[...]
Cc: stable@vger.kernel.org
Fixes: f57f3df03a8e ("ALSA: pcm: More fine-grained PCM link locking")
Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
---
sound/core/pcm_native.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index 3ad399cb6f30..5b36881f7095 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -138,6 +138,16 @@ void snd_pcm_stream_lock_irq(struct snd_pcm_substream *substream)
}
EXPORT_SYMBOL_GPL(snd_pcm_stream_lock_irq);
+static void snd_pcm_stream_lock_nested(struct snd_pcm_substream *substream)
+{
+ struct snd_pcm_group *group = &substream->self_group;
+
+ if (substream->pcm->nonatomic)
+ mutex_lock_nested(&group->mutex, SINGLE_DEPTH_NESTING);
+ else
+ spin_lock_nested(&group->lock, SINGLE_DEPTH_NESTING);
+}
+
/**
* snd_pcm_stream_unlock_irq - Unlock the PCM stream
* @substream: PCM substream
@@ -2200,7 +2210,7 @@ static int snd_pcm_link(struct snd_pcm_substream *substream, int fd)
snd_pcm_stream_unlock_irq(substream);
snd_pcm_group_lock_irq(target_group, nonatomic);
- snd_pcm_stream_lock(substream1);
+ snd_pcm_stream_lock_nested(substream1);
snd_pcm_group_assign(substream1, target_group);
refcount_inc(&target_group->refs);
snd_pcm_stream_unlock(substream1);
@@ -2216,7 +2226,7 @@ static int snd_pcm_link(struct snd_pcm_substream *substream, int fd)
static void relink_to_local(struct snd_pcm_substream *substream)
{
- snd_pcm_stream_lock(substream);
+ snd_pcm_stream_lock_nested(substream);
snd_pcm_group_assign(substream, &substream->self_group);
snd_pcm_stream_unlock(substream);
}
--
2.20.1
^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH 1/2] ALSA: pcm: disallow linking stream to itself
2020-06-08 10:06 ` [PATCH 1/2] ALSA: pcm: disallow linking stream to itself Michał Mirosław
@ 2020-06-08 12:48 ` Takashi Iwai
2020-06-08 16:50 ` [PATCH v2] " Michał Mirosław
0 siblings, 1 reply; 7+ messages in thread
From: Takashi Iwai @ 2020-06-08 12:48 UTC (permalink / raw)
To: Michał Mirosław
Cc: Jaroslav Kysela, Takashi Iwai, alsa-devel, linux-kernel
On Mon, 08 Jun 2020 12:06:32 +0200,
Michał Mirosław wrote:
>
> Prevent SNDRV_PCM_IOCTL_LINK linking stream to itself - the code
> can't handle it. Fixed commit is not where bug was introduced, but
> changes the context significantly.
>
> Cc: stable@vger.kernel.org
> Fixes: 0888c321de70 ("pcm_native: switch to fdget()/fdput()")
> Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Thanks for the fix. Just a minor point:
> @@ -2166,6 +2166,12 @@ static int snd_pcm_link(struct snd_pcm_substream *substream, int fd)
> }
> pcm_file = f.file->private_data;
> substream1 = pcm_file->substream;
> +
> + if (substream == substream1) {
> + res = -EDEADLK;
We've never used this error code, hence it may confuse the user-space
side. I'd use a more standard -EINVAL instead; the error is basically
an invalid argument, after all.
thanks,
Takashi
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH 2/2] ALSA: pcm: fix snd_pcm_link() lockdep splat
2020-06-08 10:06 ` [PATCH 2/2] ALSA: pcm: fix snd_pcm_link() lockdep splat Michał Mirosław
@ 2020-06-08 13:02 ` Takashi Iwai
0 siblings, 0 replies; 7+ messages in thread
From: Takashi Iwai @ 2020-06-08 13:02 UTC (permalink / raw)
To: Michał Mirosław
Cc: Jaroslav Kysela, Takashi Iwai, alsa-devel, linux-kernel
On Mon, 08 Jun 2020 12:06:32 +0200,
Michał Mirosław wrote:
>
> Add and use snd_pcm_stream_lock_nested() in snd_pcm_link/unlink
> implementation. The code is fine, but generates a lockdep complaint:
>
> ============================================
> WARNING: possible recursive locking detected
> 5.7.1mq+ #381 Tainted: G O
> --------------------------------------------
> pulseaudio/4180 is trying to acquire lock:
> ffff888402d6f508 (&group->lock){-...}-{2:2}, at: snd_pcm_common_ioctl+0xda8/0xee0 [snd_pcm]
>
> but task is already holding lock:
> ffff8883f7a8cf18 (&group->lock){-...}-{2:2}, at: snd_pcm_common_ioctl+0xe4e/0xee0 [snd_pcm]
>
> other info that might help us debug this:
> Possible unsafe locking scenario:
>
> CPU0
> ----
> lock(&group->lock);
> lock(&group->lock);
>
> *** DEADLOCK ***
>
> May be due to missing lock nesting notation
>
> 2 locks held by pulseaudio/4180:
> #0: ffffffffa1a05190 (snd_pcm_link_rwsem){++++}-{3:3}, at: snd_pcm_common_ioctl+0xca0/0xee0 [snd_pcm]
> #1: ffff8883f7a8cf18 (&group->lock){-...}-{2:2}, at: snd_pcm_common_ioctl+0xe4e/0xee0 [snd_pcm]
> [...]
>
> Cc: stable@vger.kernel.org
> Fixes: f57f3df03a8e ("ALSA: pcm: More fine-grained PCM link locking")
> Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Applied now. Thanks.
Takashi
^ permalink raw reply [flat|nested] 7+ messages in thread
* [PATCH v2] ALSA: pcm: disallow linking stream to itself
2020-06-08 12:48 ` Takashi Iwai
@ 2020-06-08 16:50 ` Michał Mirosław
2020-06-08 17:35 ` Takashi Iwai
0 siblings, 1 reply; 7+ messages in thread
From: Michał Mirosław @ 2020-06-08 16:50 UTC (permalink / raw)
To: Jaroslav Kysela, Takashi Iwai; +Cc: alsa-devel, linux-kernel
Prevent SNDRV_PCM_IOCTL_LINK linking stream to itself - the code
can't handle it. Fixed commit is not where bug was introduced, but
changes the context significantly.
Cc: stable@vger.kernel.org
Fixes: 0888c321de70 ("pcm_native: switch to fdget()/fdput()")
Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
---
v2: EDEADLK -> EINVAL
---
sound/core/pcm_native.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index aef860256278..434e7b604bad 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -2166,6 +2166,12 @@ static int snd_pcm_link(struct snd_pcm_substream *substream, int fd)
}
pcm_file = f.file->private_data;
substream1 = pcm_file->substream;
+
+ if (substream == substream1) {
+ res = -EINVAL;
+ goto _badf;
+ }
+
group = kzalloc(sizeof(*group), GFP_KERNEL);
if (!group) {
res = -ENOMEM;
--
2.20.1
^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH v2] ALSA: pcm: disallow linking stream to itself
2020-06-08 16:50 ` [PATCH v2] " Michał Mirosław
@ 2020-06-08 17:35 ` Takashi Iwai
0 siblings, 0 replies; 7+ messages in thread
From: Takashi Iwai @ 2020-06-08 17:35 UTC (permalink / raw)
To: Michał Mirosław
Cc: Jaroslav Kysela, Takashi Iwai, alsa-devel, linux-kernel
On Mon, 08 Jun 2020 18:50:39 +0200,
Michał Mirosław wrote:
>
> Prevent SNDRV_PCM_IOCTL_LINK linking stream to itself - the code
> can't handle it. Fixed commit is not where bug was introduced, but
> changes the context significantly.
>
> Cc: stable@vger.kernel.org
> Fixes: 0888c321de70 ("pcm_native: switch to fdget()/fdput()")
> Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
> ---
> v2: EDEADLK -> EINVAL
Applied now. Thanks!
Takashi
^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2020-06-08 17:36 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
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2020-06-08 10:06 [PATCH 0/2] ALSA: pcm: stream linking locking fixes Michał Mirosław
2020-06-08 10:06 ` [PATCH 2/2] ALSA: pcm: fix snd_pcm_link() lockdep splat Michał Mirosław
2020-06-08 13:02 ` Takashi Iwai
2020-06-08 10:06 ` [PATCH 1/2] ALSA: pcm: disallow linking stream to itself Michał Mirosław
2020-06-08 12:48 ` Takashi Iwai
2020-06-08 16:50 ` [PATCH v2] " Michał Mirosław
2020-06-08 17:35 ` Takashi Iwai
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