From patchwork Fri Dec 7 16:05:45 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: [3.5.y.z, extended, stable] Patch "ALSA: usb-audio: Fix mutex deadlock at disconnection" has been added to staging queue Date: Fri, 07 Dec 2012 06:05:45 -0000 From: Herton Ronaldo Krzesinski X-Patchwork-Id: 204557 Message-Id: <1354896345-22832-1-git-send-email-herton.krzesinski@canonical.com> To: Takashi Iwai Cc: kernel-team@lists.ubuntu.com, Jiri Slaby This is a note to let you know that I have just added a patch titled ALSA: usb-audio: Fix mutex deadlock at disconnection to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree which can be found at: http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.5.y.z tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Herton ------ >From d3418cabb47e8c754ac2f199d6e9f3efc7b03117 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 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 Signed-off-by: Takashi Iwai Signed-off-by: Herton Ronaldo Krzesinski --- sound/usb/card.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) -- 1.7.9.5 diff --git a/sound/usb/card.c b/sound/usb/card.c index 486b4a6..b3f5ad4 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); } }