[3.16.y-ckt extended stable] Patch "usb: musb: cppi41: restart hrtimer only if not yet done" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    usb: musb: cppi41: restart hrtimer only if not yet done

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt1.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From e74dd34fdd3a432875e2a9289355a1ee9a171c95 Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx at linutronix.de>
Date: Thu, 2 Oct 2014 17:32:16 +0200
Subject: usb: musb: cppi41: restart hrtimer only if not yet done

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 at linutronix.de>
Signed-off-by: Thomas Gleixner <tglx at linutronix.de>
[bigeasy: collected information and created a patch + description based
          on it]
Signed-off-by: Sebastian Andrzej Siewior <bigeasy at linutronix.de>
Signed-off-by: Felipe Balbi <balbi at ti.com>
Signed-off-by: Luis Henriques <luis.henriques at 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 5341bb223b7c..b4fe70355682 100644
--- a/drivers/usb/musb/musb_cppi41.c
+++ b/drivers/usb/musb/musb_cppi41.c
@@ -230,7 +230,8 @@ 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));
--
2.1.0