linux-kernel - [PATCH tip/core/rcu 4/5] rcu: Fix precedence error in cpu_needs_another

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Date:	Tue, 30 Oct 2012 10:19:22 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
	josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, edumazet@...gle.com, darren@...art.com,
	fweisbec@...il.com, sbw@....edu, patches@...aro.org,
	"Paul E. McKenney" <paul.mckenney@...aro.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 4/5] rcu: Fix precedence error in cpu_needs_another_gp()

From: "Paul E. McKenney" <paul.mckenney@...aro.org>

The fix introduced by a10d206e (rcu: Fix day-one dyntick-idle
stall-warning bug) has a C-language precedence error.  It turns out
that this error is harmless in that the same result is computed for all
inputs, but the code is nevertheless a potential source of confusion.
This commit therefore introduces parentheses in order to force the
execution of the code to reflect the intent.

Reported-by: Ben Hutchings <ben@...adent.org.uk>
Signed-off-by: Paul E. McKenney <paul.mckenney@...aro.org>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 kernel/rcutree.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index f9c17c3..effd47a 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -313,7 +313,7 @@ static int
 cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
 {
 	return *rdp->nxttail[RCU_DONE_TAIL +
-			     ACCESS_ONCE(rsp->completed) != rdp->completed] &&
+			     (ACCESS_ONCE(rsp->completed) != rdp->completed)] &&
 	       !rcu_gp_in_progress(rsp);
 }
 
-- 
1.7.8

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