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    Subject[PATCH 3.13 129/162] usb: musb: cppi41: restart hrtimer only if not yet done
    Date
    3.13.11.11 -stable review patch.  If anyone has any objections, please let me know.

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

    From: Thomas Gleixner <tglx@linutronix.de>

    commit d2e6d62c9cbbc2da4211f672dbeea08960e29a80 upstream.

    commit c58d80f52 ("usb: musb: Ensure that cppi41 timer gets armed on
    premature DMA TX irq") fixed hrtimer scheduling bug. There is one left
    which does not trigger that often.
    The following scenario is still possible:

    lock(&x->lock);
    hrtimer_start(&x->t);
    unlock(&x->lock);

    expires:
    t->function();
    lock(&x->lock);
    lock(&x->lock); if (!hrtimer_queued(&x->t))
    hrtimer_start(&x->t);
    unlock(&x->lock);

    if (!list_empty(x->early_tx_list))
    ret = HRTIMER_RESTART;
    -> hrtimer_forward_now(...)
    } else
    ret = HRTIMER_NORESTART;

    unlock(&x->lock);

    and the timer callback returns HRTIMER_RESTART for an armed timer. This
    is wrong and we run into the BUG_ON() in __run_hrtimer().
    This can happens on SMP or PREEMPT-RT.
    The patch fixes the problem by only starting the timer if the timer is
    not yet queued.

    Reported-by: Torben Hohn <torbenh@linutronix.de>
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    [bigeasy: collected information and created a patch + description based
    on it]
    Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
    Signed-off-by: Felipe Balbi <balbi@ti.com>

    Signed-off-by: Kamal Mostafa <kamal@canonical.com>
    ---
    drivers/usb/musb/musb_cppi41.c | 3 ++-
    1 file changed, 2 insertions(+), 1 deletion(-)

    diff --git a/drivers/usb/musb/musb_cppi41.c b/drivers/usb/musb/musb_cppi41.c
    index 4a5af5c..3faaeb7 100644
    --- a/drivers/usb/musb/musb_cppi41.c
    +++ b/drivers/usb/musb/musb_cppi41.c
    @@ -190,7 +190,8 @@ static enum hrtimer_restart cppi41_recheck_tx_req(struct hrtimer *timer)
    }
    }

    - if (!list_empty(&controller->early_tx_list)) {
    + if (!list_empty(&controller->early_tx_list) &&
    + !hrtimer_is_queued(&controller->early_tx)) {
    ret = HRTIMER_RESTART;
    hrtimer_forward_now(&controller->early_tx,
    ktime_set(0, 150 * NSEC_PER_USEC));
    --
    1.9.1


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