forked from Minki/linux
ALSA: oss: Fix potential deadlock at unregistration
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>
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@ -162,7 +162,6 @@ int snd_unregister_oss_device(int type, struct snd_card *card, int dev)
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mutex_unlock(&sound_oss_mutex);
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mutex_unlock(&sound_oss_mutex);
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return -ENOENT;
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return -ENOENT;
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}
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}
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unregister_sound_special(minor);
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switch (SNDRV_MINOR_OSS_DEVICE(minor)) {
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switch (SNDRV_MINOR_OSS_DEVICE(minor)) {
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case SNDRV_MINOR_OSS_PCM:
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case SNDRV_MINOR_OSS_PCM:
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track2 = SNDRV_MINOR_OSS(cidx, SNDRV_MINOR_OSS_AUDIO);
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track2 = SNDRV_MINOR_OSS(cidx, SNDRV_MINOR_OSS_AUDIO);
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@ -174,12 +173,18 @@ int snd_unregister_oss_device(int type, struct snd_card *card, int dev)
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track2 = SNDRV_MINOR_OSS(cidx, SNDRV_MINOR_OSS_DMMIDI1);
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track2 = SNDRV_MINOR_OSS(cidx, SNDRV_MINOR_OSS_DMMIDI1);
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break;
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break;
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}
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}
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if (track2 >= 0) {
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if (track2 >= 0)
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unregister_sound_special(track2);
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snd_oss_minors[track2] = NULL;
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snd_oss_minors[track2] = NULL;
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}
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snd_oss_minors[minor] = NULL;
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snd_oss_minors[minor] = NULL;
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mutex_unlock(&sound_oss_mutex);
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mutex_unlock(&sound_oss_mutex);
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/* call unregister_sound_special() outside sound_oss_mutex;
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* otherwise may deadlock, as it can trigger the release of a card
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*/
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unregister_sound_special(minor);
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if (track2 >= 0)
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unregister_sound_special(track2);
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kfree(mptr);
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kfree(mptr);
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return 0;
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return 0;
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}
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}
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