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author | Takashi Iwai <tiwai@suse.de> | 2012-11-13 11:22:48 +0100 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2012-11-17 13:16:36 -0800 |
commit | 2ce3809e3420701b66bb4a6bebc69ddaf850394f (patch) | |
tree | c4f0b0a032903b72c98d0558e71beb227b1495bd /sound/usb/card.c | |
parent | 32896690903c576809f21724115612a82a102a52 (diff) | |
download | linux-stable-2ce3809e3420701b66bb4a6bebc69ddaf850394f.tar.gz linux-stable-2ce3809e3420701b66bb4a6bebc69ddaf850394f.tar.bz2 linux-stable-2ce3809e3420701b66bb4a6bebc69ddaf850394f.zip |
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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'sound/usb/card.c')
-rw-r--r-- | sound/usb/card.c | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/sound/usb/card.c b/sound/usb/card.c index 147a5c42b95d..388460d27311 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(®ister_mutex); down_write(&chip->shutdown_rwsem); chip->shutdown = 1; + up_write(&chip->shutdown_rwsem); + + mutex_lock(®ister_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(®ister_mutex); snd_card_free_when_closed(card); } else { - up_write(&chip->shutdown_rwsem); mutex_unlock(®ister_mutex); } } |