[PATCH 4.2.y-ckt 14/64] timerfd: Handle relative timers with CONFIG_TIME_LOW_RES proper

[Kamal Mostafa]

4.2.8-ckt4 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Thomas Gleixner <tglx at linutronix.de>

commit b62526ed11a1fe3861ab98d40b7fdab8981d788a upstream.

Helge reported that a relative timer can return a remaining time larger than
the programmed relative time on parisc and other architectures which have
CONFIG_TIME_LOW_RES set. This happens because we add a jiffie to the resulting
expiry time to prevent short timeouts.

Use the new function hrtimer_expires_remaining_adjusted() to calculate the
remaining time. It takes that extra added time into account for relative
timers.

Reported-and-tested-by: Helge Deller <deller at gmx.de>
Signed-off-by: Thomas Gleixner <tglx at linutronix.de>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: John Stultz <john.stultz at linaro.org>
Cc: linux-m68k at lists.linux-m68k.org
Cc: dhowells at redhat.com
Link: http://lkml.kernel.org/r/20160114164159.354500742@linutronix.de
Signed-off-by: Thomas Gleixner <tglx at linutronix.de>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 fs/timerfd.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/timerfd.c b/fs/timerfd.c
index b94fa6c..053818d 100644
--- a/fs/timerfd.c
+++ b/fs/timerfd.c
@@ -153,7 +153,7 @@ static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx)
 	if (isalarm(ctx))
 		remaining = alarm_expires_remaining(&ctx->t.alarm);
 	else
-		remaining = hrtimer_expires_remaining(&ctx->t.tmr);
+		remaining = hrtimer_expires_remaining_adjusted(&ctx->t.tmr);
 
 	return remaining.tv64 < 0 ? ktime_set(0, 0): remaining;
 }
-- 
1.9.1