linux-kernel - [PATCH 3.16 002/136] tick: broadcast-hrtimer: Remove overly clever return value abuse

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Date:   Tue, 17 Dec 2019 00:45:36 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Frederic Weisbecker" <fweisbec@...il.com>,
        "Viresh Kumar" <viresh.kumar@...aro.org>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Peter Zijlstra" <peterz@...radead.org>,
        "Preeti U Murthy" <preeti@...ux.vnet.ibm.com>,
        "Marcelo Tosatti" <mtosatti@...hat.com>
Subject: [PATCH 3.16 002/136] tick: broadcast-hrtimer: Remove overly
 clever return value abuse

3.16.80-rc1 review patch.  If anyone has any objections, please let me know.

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

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

commit b8a62f1ff0ccb18fdc25c6150d1cd394610f4753 upstream.

The assignment of bc_moved in the conditional construct relies on the
fact that in the case of hrtimer_start() invocation the return value
is always 0. It took me a while to understand it.

We want to get rid of the hrtimer_start() return value. Open code the
logic which makes it readable as well.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Preeti U Murthy <preeti@...ux.vnet.ibm.com>
Acked-by: Peter Zijlstra <peterz@...radead.org>
Cc: Viresh Kumar <viresh.kumar@...aro.org>
Cc: Marcelo Tosatti <mtosatti@...hat.com>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Link: http://lkml.kernel.org/r/20150414203503.404751457@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
[bwh: Backported to 3.16 to ease backporting commit b9023b91dd02
 "tick: broadcast-hrtimer: Fix a race in bc_set_next"]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 kernel/time/tick-broadcast-hrtimer.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

--- a/kernel/time/tick-broadcast-hrtimer.c
+++ b/kernel/time/tick-broadcast-hrtimer.c
@@ -66,9 +66,11 @@ static int bc_set_next(ktime_t expires,
 	 * hrtimer_{start/cancel} functions call into tracing,
 	 * calls to these functions must be bound within RCU_NONIDLE.
 	 */
-	RCU_NONIDLE(bc_moved = (hrtimer_try_to_cancel(&bctimer) >= 0) ?
-		!hrtimer_start(&bctimer, expires, HRTIMER_MODE_ABS_PINNED) :
-			0);
+	RCU_NONIDLE({
+			bc_moved = hrtimer_try_to_cancel(&bctimer) >= 0;
+			if (bc_moved)
+				hrtimer_start(&bctimer, expires,
+					      HRTIMER_MODE_ABS_PINNED);});
 	if (bc_moved) {
 		/* Bind the "device" to the cpu */
 		bc->bound_on = smp_processor_id();