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Commit 382225e6 authored by Takashi Iwai's avatar Takashi Iwai
Browse files

ALSA: usb-audio: fix oops due to cleanup race when disconnecting 



When a USB audio device is disconnected, snd_usb_audio_disconnect()
kills all audio URBs.  At the same time, the application, after being
notified of the disconnection, might close the device, in which case
ALSA calls the .hw_free callback, which should free the URBs too.

Commit de1b8b93 "[ALSA] Fix hang-up at disconnection of usb-audio"
prevented snd_usb_hw_free() from freeing the URBs to avoid a hang that
resulted from this race, but this introduced another race because the
URB callbacks could now be executed after snd_usb_hw_free() has
returned, and try to access already freed data.

Fix the first race by introducing a mutex to serialize the disconnect
callback and all PCM callbacks that manage URBs (hw_free and hw_params).

Reported-and-tested-by: default avatarPierre-Louis Bossart <pierre-louis.bossart@intel.com>
Cc: <stable@kernel.org>
[CL: also serialize hw_params callback]
Signed-off-by: default avatarClemens Ladisch <clemens@ladisch.de>
Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
parent 30649676

sound/usb/card.c

+4 −0
Original line number Diff line number Diff line
@@ -323,6 +323,7 @@ static int snd_usb_audio_create(struct usb_device *dev, int idx, 
		return -ENOMEM;

	}



	mutex_init(&chip->shutdown_mutex);

	chip->index = idx;

	chip->dev = dev;

	chip->card = card;
@@ -531,6 +532,7 @@ static void snd_usb_audio_disconnect(struct usb_device *dev, void *ptr) 
	chip = ptr;

	card = chip->card;

	mutex_lock(&register_mutex);

	mutex_lock(&chip->shutdown_mutex);

	chip->shutdown = 1;

	chip->num_interfaces--;

	if (chip->num_interfaces <= 0) {
@@ -548,9 +550,11 @@ static void snd_usb_audio_disconnect(struct usb_device *dev, void *ptr) 
			snd_usb_mixer_disconnect(p);

		}

		usb_chip[chip->index] = NULL;

		mutex_unlock(&chip->shutdown_mutex);

		mutex_unlock(&register_mutex);

		snd_card_free_when_closed(card);

	} else {

		mutex_unlock(&chip->shutdown_mutex);

		mutex_unlock(&register_mutex);

	}

}

sound/usb/pcm.c

+5 −2
Original line number Diff line number Diff line
@@ -361,6 +361,7 @@ static int snd_usb_hw_params(struct snd_pcm_substream *substream, 
	}



	if (changed) {

		mutex_lock(&subs->stream->chip->shutdown_mutex);

		/* format changed */

		snd_usb_release_substream_urbs(subs, 0);

		/* influenced: period_bytes, channels, rate, format, */
@@ -368,6 +369,7 @@ static int snd_usb_hw_params(struct snd_pcm_substream *substream, 
						  params_rate(hw_params),

						  snd_pcm_format_physical_width(params_format(hw_params)) *

							params_channels(hw_params));

		mutex_unlock(&subs->stream->chip->shutdown_mutex);

	}



	return ret;
@@ -385,8 +387,9 @@ static int snd_usb_hw_free(struct snd_pcm_substream *substream) 
	subs->cur_audiofmt = NULL;

	subs->cur_rate = 0;

	subs->period_bytes = 0;

	if (!subs->stream->chip->shutdown)

	mutex_lock(&subs->stream->chip->shutdown_mutex);

	snd_usb_release_substream_urbs(subs, 0);

	mutex_unlock(&subs->stream->chip->shutdown_mutex);

	return snd_pcm_lib_free_vmalloc_buffer(substream);

}

sound/usb/usbaudio.h

+1 −0
Original line number Diff line number Diff line
@@ -36,6 +36,7 @@ struct snd_usb_audio { 
	struct snd_card *card;

	u32 usb_id;

	int shutdown;

	struct mutex shutdown_mutex;

	unsigned int txfr_quirk:1; /* Subframe boundaries on transfers */

	int num_interfaces;

	int num_suspended_intf;