linux-kernel - [PATCH] Wait to remove active timer when rescheduling hrtimer

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Date:	Fri, 21 Jan 2011 09:52:30 -0800
From:	Vernon Mauery <vernux@...ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Vernon Mauery <vernux@...ibm.com>
Subject: [PATCH] Wait to remove active timer when rescheduling hrtimer

In the current hrtimer implementation, when explicitly
removing a timer, the hrtimer_cancel function waits
until the timer is not currently running before actually
calling remove_hrtimer.  But in the __hrtimer_start_range_ns
function (called by hrtimer_start, among others), it
calls remove_hrtimer without checking to see if the
timer is currently running.  This doesn't seem to cause
much trouble in the vanilla kernel, but in the -RT
kernel, this causes a silent hang when exercising the
sch_htb module on a 10GbE interface.

Signed-off-by: Vernon Mauery <vernux@...ibm.com>
---
 kernel/hrtimer.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index 0c8d7c0..c7e8ba0 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -935,6 +935,11 @@ int __hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim,
 	base = lock_hrtimer_base(timer, &flags);

 	/* Remove an active timer from the queue: */
+	while (hrtimer_callback_running(timer)) {
+		unlock_hrtimer_base(timer, &flags);
+		hrtimer_wait_for_timer(timer);
+		base = lock_hrtimer_base(timer, &flags);
+	}
 	ret = remove_hrtimer(timer, base);

 	/* Switch the timer base, if necessary: */
-- 
1.7.1

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