Subject: timer-fd: Prevent live lock
From: Thomas Gleixner <tglx@linutronix.de>
Date: Wed, 25 Jan 2012 11:08:40 +0100
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.6/older/patches-4.6.2-rt5.tar.xz

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>

---
 fs/timerfd.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/fs/timerfd.c
+++ b/fs/timerfd.c
@@ -450,7 +450,10 @@ static int do_timerfd_settime(int ufd, i
 				break;
 		}
 		spin_unlock_irq(&ctx->wqh.lock);
-		cpu_relax();
+		if (isalarm(ctx))
+			hrtimer_wait_for_timer(&ctx->t.alarm.timer);
+		else
+			hrtimer_wait_for_timer(&ctx->t.tmr);
 	}
 
 	/*
