From 10e44239f67d0b6fb74006e61a7e883b8075247a Mon Sep 17 00:00:00 2001 From: Takashi Iwai Date: Tue, 13 Nov 2012 11:22:48 +0100 Subject: [PATCH] ALSA: usb-audio: Fix mutex deadlock at disconnection 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 Cc: Signed-off-by: Takashi Iwai --- sound/usb/card.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/sound/usb/card.c b/sound/usb/card.c index 282f0fc9fed1..dbf7999d18b4 100644 --- a/sound/usb/card.c +++ b/sound/usb/card.c @@ -559,9 +559,11 @@ 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); @@ -582,11 +584,9 @@ 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); } } -- 2.20.1