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    Subject[51/78] ALSA: aloop - Fix possible IRQ lock inversion
    2.6.38-stable review patch.  If anyone has any objections, please let us know.

    ------------------

    From: Takashi Iwai <tiwai@suse.de>

    commit 98d21df431ad55281e1abf780f8d51e3391900b2 upstream.

    loopback_pos_update() can be called in the timer callback, thus the lock
    held should be irq-safe. Otherwise you'll get AB/BA deadlock together
    with substream->self_group.lock.

    Reported-and-tested-by: Knut Petersen <Knut_Petersen@t-online.de>
    Signed-off-by: Takashi Iwai <tiwai@suse.de>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    sound/drivers/aloop.c | 19 +++++++++----------
    1 file changed, 9 insertions(+), 10 deletions(-)

    --- a/sound/drivers/aloop.c
    +++ b/sound/drivers/aloop.c
    @@ -482,8 +482,9 @@ static unsigned int loopback_pos_update(
    cable->streams[SNDRV_PCM_STREAM_CAPTURE];
    unsigned long delta_play = 0, delta_capt = 0;
    unsigned int running;
    + unsigned long flags;

    - spin_lock(&cable->lock);
    + spin_lock_irqsave(&cable->lock, flags);
    running = cable->running ^ cable->pause;
    if (running & (1 << SNDRV_PCM_STREAM_PLAYBACK)) {
    delta_play = jiffies - dpcm_play->last_jiffies;
    @@ -495,10 +496,8 @@ static unsigned int loopback_pos_update(
    dpcm_capt->last_jiffies += delta_capt;
    }

    - if (delta_play == 0 && delta_capt == 0) {
    - spin_unlock(&cable->lock);
    - return running;
    - }
    + if (delta_play == 0 && delta_capt == 0)
    + goto unlock;

    if (delta_play > delta_capt) {
    loopback_bytepos_update(dpcm_play, delta_play - delta_capt,
    @@ -510,14 +509,14 @@ static unsigned int loopback_pos_update(
    delta_capt = delta_play;
    }

    - if (delta_play == 0 && delta_capt == 0) {
    - spin_unlock(&cable->lock);
    - return running;
    - }
    + if (delta_play == 0 && delta_capt == 0)
    + goto unlock;
    +
    /* note delta_capt == delta_play at this moment */
    loopback_bytepos_update(dpcm_capt, delta_capt, BYTEPOS_UPDATE_COPY);
    loopback_bytepos_update(dpcm_play, delta_play, BYTEPOS_UPDATE_POSONLY);
    - spin_unlock(&cable->lock);
    + unlock:
    + spin_unlock_irqrestore(&cable->lock, flags);
    return running;
    }




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