linux-kernel - [tip:timers/urgent] timerfd: Handle relative timers with CONFIG_TIME_LOW

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Date:	Sun, 17 Jan 2016 02:43:04 -0800
From:	tip-bot for Thomas Gleixner <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	john.stultz@...aro.org, peterz@...radead.org, tglx@...utronix.de,
	linux-kernel@...r.kernel.org, mingo@...nel.org, deller@....de,
	hpa@...or.com
Subject: [tip:timers/urgent] timerfd:
  Handle relative timers with CONFIG_TIME_LOW_RES proper

Commit-ID:  b62526ed11a1fe3861ab98d40b7fdab8981d788a
Gitweb:     http://git.kernel.org/tip/b62526ed11a1fe3861ab98d40b7fdab8981d788a
Author:     Thomas Gleixner <tglx@...utronix.de>
AuthorDate: Thu, 14 Jan 2016 16:54:46 +0000
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Sun, 17 Jan 2016 11:13:55 +0100

timerfd: Handle relative timers with CONFIG_TIME_LOW_RES proper

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@....de>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: John Stultz <john.stultz@...aro.org>
Cc: linux-m68k@...ts.linux-m68k.org
Cc: dhowells@...hat.com
Cc: stable@...r.kernel.org
Link: http://lkml.kernel.org/r/20160114164159.354500742@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 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;
 }