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    SubjectRe: [BUG][2.6.38] IRQ Lock Inversion / i915 fails
    At Thu, 17 Mar 2011 09:55:47 -0700,
    Linus Torvalds wrote:
    >
    > On Thu, Mar 17, 2011 at 2:40 AM, Knut Petersen
    > <Knut_Petersen@t-online.de> wrote:
    > >
    > > Well, I updated my test partition to opensuse 11.4.
    > >
    > > The opensuse standard kernel is unusable for me, booting hangs
    > > most of the time, the same is true for shutdown. If booting succeeds the
    > > system will fail after a short time of usage.
    > >
    > > So I installed kernel 2.6.38.  That helped a lot ... for a few minutes.
    > >
    > > A possible irq lock inversion is detected during boot, after a short time
    > > X fails, restarting the X server does not work, a reboot is necessary.
    >
    > Ok, so the lock inversion seems to be due to the sound/drivers/aloop.c
    > file, where the function "loopback_pos_update()" gets called from
    > within a softirq context. And it takes a lock (cable->lock) that is
    > also taken unprotected by loopback_trigger(). So that's liable to
    > deadlock as per lockdep. Jaroslav? Takashi?

    The trigger callback should be called always in irq-disabled context,
    so this should be OK. But loopback_pos_update() is called in the
    timer callback, and this can be the issue.

    Knut, how about the patch below?


    thanks,

    Takashi

    ---
    diff --git a/sound/drivers/aloop.c b/sound/drivers/aloop.c
    index 12b44b0..a0da775 100644
    --- a/sound/drivers/aloop.c
    +++ b/sound/drivers/aloop.c
    @@ -482,8 +482,9 @@ static unsigned int loopback_pos_update(struct loopback_cable *cable)
    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(struct loopback_cable *cable)
    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(struct loopback_cable *cable)
    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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