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authorTakashi Iwai <tiwai@suse.de>2012-11-13 11:22:48 +0100
committerBen Hutchings <ben@decadent.org.uk>2012-11-16 16:47:21 +0000
commitc585c4e138c4688a1492e7f8f0515eadae653040 (patch)
tree366d38d50b5e38639432843f203c83a50752bd20
parentbaf6d74e8693f8e71ccd2c47f0e1ee4480c9744f (diff)
ALSA: usb-audio: Fix mutex deadlock at disconnection
commit 10e44239f67d0b6fb74006e61a7e883b8075247a upstream. The recent change for USB-audio disconnection race fixes introduced a mutex deadlock again. There is a circular dependency between chip->shutdown_rwsem and pcm->open_mutex, depicted like below, when a device is opened during the disconnection operation: A. snd_usb_audio_disconnect() -> card.c::register_mutex -> chip->shutdown_rwsem (write) -> snd_card_disconnect() -> pcm.c::register_mutex -> pcm->open_mutex B. snd_pcm_open() -> pcm->open_mutex -> snd_usb_pcm_open() -> chip->shutdown_rwsem (read) Since the chip->shutdown_rwsem protection in the case A is required only for turning on the chip->shutdown flag and it doesn't have to be taken for the whole operation, we can reduce its window in snd_usb_audio_disconnect(). Reported-by: Jiri Slaby <jslaby@suse.cz> Signed-off-by: Takashi Iwai <tiwai@suse.de> Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
-rw-r--r--sound/usb/card.c6
1 files changed, 3 insertions, 3 deletions
diff --git a/sound/usb/card.c b/sound/usb/card.c
index 7003c1317723..566acb319581 100644
--- a/sound/usb/card.c
+++ b/sound/usb/card.c
@@ -555,9 +555,11 @@ static void snd_usb_audio_disconnect(struct usb_device *dev,
return;
card = chip->card;
- mutex_lock(&register_mutex);
down_write(&chip->shutdown_rwsem);
chip->shutdown = 1;
+ up_write(&chip->shutdown_rwsem);
+
+ mutex_lock(&register_mutex);
chip->num_interfaces--;
if (chip->num_interfaces <= 0) {
snd_card_disconnect(card);
@@ -574,11 +576,9 @@ static void snd_usb_audio_disconnect(struct usb_device *dev,
snd_usb_mixer_disconnect(p);
}
usb_chip[chip->index] = NULL;
- up_write(&chip->shutdown_rwsem);
mutex_unlock(&register_mutex);
snd_card_free_when_closed(card);
} else {
- up_write(&chip->shutdown_rwsem);
mutex_unlock(&register_mutex);
}
}