timer-fd-avoid-live-lock.patch

Subject: timer-fd: Prevent live lock
From: Thomas Gleixner <tglx@linutronix.de>
Date: Wed, 25 Jan 2012 11:08:40 +0100

If hrtimer_try_to_cancel() requires a retry, then depending on the
priority setting te retry loop might prevent timer callback completion
on RT. Prevent that by waiting for completion on RT, no change for a
non RT kernel.

Reported-by: Sankara Muthukrishnan <sankara.m@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable-rt@vger.kernel.org
---
 fs/timerfd.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-stable/fs/timerfd.c
===================================================================
--- linux-stable.orig/fs/timerfd.c
+++ linux-stable/fs/timerfd.c
@@ -313,7 +313,7 @@ SYSCALL_DEFINE4(timerfd_settime, int, uf
 		if (hrtimer_try_to_cancel(&ctx->tmr) >= 0)
 			break;
 		spin_unlock_irq(&ctx->wqh.lock);
-		cpu_relax();
+		hrtimer_wait_for_timer(&ctx->tmr);
 	}
 
 	/*