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authorTakashi Iwai <tiwai@suse.de>2012-11-13 11:22:48 +0100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2012-11-17 13:19:06 -0800
commit118ff53fa02dc7830e2f561b6aa2619ef41de6ab (patch)
treefe656eebebb2f3a610c95df9e6013cbaacc28ab2 /Makefile
parentf49c1beea97dfea9acb4a4dc213c12cf040b0280 (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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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