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ALSA: oss: Fix potential deadlock at unregistration

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We took sound_oss_mutex around the calls of unregister_sound_special()
at unregistering OSS devices.  This may, however, lead to a deadlock,
because we manage the card release via the card's device object, and
the release may happen at unregister_sound_special() call -- which
will take sound_oss_mutex again in turn.

Although the deadlock might be fixed by relaxing the rawmidi mutex in
the previous commit, it's safer to move unregister_sound_special()
calls themselves out of the sound_oss_mutex, too.  The call is
race-safe as the function has a spinlock protection by itself.

Link: https://lore.kernel.org/r/CAB7eexJP7w1B0mVgDF0dQ+gWor7UdkiwPczmL7pn91xx8xpzOA@mail.gmail.com
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20221011070147.7611-2-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Takashi Iwai 2022-10-11 09:01:47 +02:00
parent a70aef7982
commit 97d917879d
1 changed files with 9 additions and 4 deletions
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13
sound/core/sound_oss.c
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@ -162,7 +162,6 @@ int snd_unregister_oss_device(int type, struct snd_card *card, int dev)
mutex_unlock(&sound_oss_mutex);
return -ENOENT;
}
unregister_sound_special(minor);
switch (SNDRV_MINOR_OSS_DEVICE(minor)) {
case SNDRV_MINOR_OSS_PCM:
track2 = SNDRV_MINOR_OSS(cidx, SNDRV_MINOR_OSS_AUDIO);
@ -174,12 +173,18 @@ int snd_unregister_oss_device(int type, struct snd_card *card, int dev)
track2 = SNDRV_MINOR_OSS(cidx, SNDRV_MINOR_OSS_DMMIDI1);
break;
}
if (track2 >= 0) {
unregister_sound_special(track2);
if (track2 >= 0)
snd_oss_minors[track2] = NULL;
}
snd_oss_minors[minor] = NULL;
mutex_unlock(&sound_oss_mutex);
/* call unregister_sound_special() outside sound_oss_mutex;
* otherwise may deadlock, as it can trigger the release of a card
*/
unregister_sound_special(minor);
if (track2 >= 0)
unregister_sound_special(track2);
kfree(mptr);
return 0;
}