[19/28] usb: musb: cppi41: restart hrtimer only if not yet done

Message ID 1413565804-13061-20-git-send-email-balbi@ti.com
State Accepted
Commit d2e6d62c9cbbc2da4211f672dbeea08960e29a80
Headers show

Commit Message

Felipe Balbi Oct. 17, 2014, 5:09 p.m.
From: Thomas Gleixner <tglx@linutronix.de>

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.

Cc: stable@vger.kernel.org
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>
---
 drivers/usb/musb/musb_cppi41.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Patch

diff --git a/drivers/usb/musb/musb_cppi41.c b/drivers/usb/musb/musb_cppi41.c
index acdfb3e..5a9b977 100644
--- a/drivers/usb/musb/musb_cppi41.c
+++ b/drivers/usb/musb/musb_cppi41.c
@@ -209,7 +209,8 @@  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, 20 * NSEC_PER_USEC));