linux-kernel - [PATCH 3.10 44/52] nohz: Fix another inconsistency between CONFIG_NO

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Message-Id: <20140624154716.124452652@linuxfoundation.org>
Date:	Tue, 24 Jun 2014 11:50:59 -0400
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Michal Hocko <mhocko@...e.cz>,
	Borislav Petkov <bp@...en8.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Rui Xiang <rui.xiang@...wei.com>
Subject: [PATCH 3.10 44/52] nohz: Fix another inconsistency between CONFIG_NO_HZ=n and nohz=off

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

------------------

From: Thomas Gleixner <tglx@...utronix.de>

commit 0e576acbc1d9600cf2d9b4a141a2554639959d50 upstream.

If CONFIG_NO_HZ=n tick_nohz_get_sleep_length() returns NSEC_PER_SEC/HZ.

If CONFIG_NO_HZ=y and the nohz functionality is disabled via the
command line option "nohz=off" or not enabled due to missing hardware
support, then tick_nohz_get_sleep_length() returns 0. That happens
because ts->sleep_length is never set in that case.

Set it to NSEC_PER_SEC/HZ when the NOHZ mode is inactive.

Reported-by: Michal Hocko <mhocko@...e.cz>
Reported-by: Borislav Petkov <bp@...en8.de>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Rui Xiang <rui.xiang@...wei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 kernel/time/tick-sched.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -720,8 +720,10 @@ static bool can_stop_idle_tick(int cpu,
 		return false;
 	}
 
-	if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE))
+	if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) {
+		ts->sleep_length = (ktime_t) { .tv64 = NSEC_PER_SEC/HZ };
 		return false;
+	}
 
 	if (need_resched())
 		return false;


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