linux-kernel - [PATCH tip/core/rcu 03/24] rcu: Shut up spurious gcc uninitialized-variable warning

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Date:	Tue, 12 May 2015 15:30:33 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...nel.org, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
	dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com,
	bobby.prani@...il.com,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 03/24] rcu: Shut up spurious gcc uninitialized-variable warning

From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>

Because gcc doesn't realize that rcu_num_lvls must be strictly greater
than zero, some versions give a spurious warning about levelcnt[0] being
uninitialized in rcu_init_one().  This commit updates the condition on
the pre-existing panic() in order to educate gcc on this point.

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 kernel/rcu/tree.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index c34422d92aa9..9b076b284695 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3982,9 +3982,9 @@ static void __init rcu_init_one(struct rcu_state *rsp,
 
 	BUILD_BUG_ON(MAX_RCU_LVLS > ARRAY_SIZE(buf));  /* Fix buf[] init! */
 
-	/* Silence gcc 4.8 warning about array index out of range. */
-	if (rcu_num_lvls > RCU_NUM_LVLS)
-		panic("rcu_init_one: rcu_num_lvls overflow");
+	/* Silence gcc 4.8 false positive about array index out of range. */
+	if (rcu_num_lvls <= 0 || rcu_num_lvls > RCU_NUM_LVLS)
+		panic("rcu_init_one: rcu_num_lvls out of range");
 
 	/* Initialize the level-tracking arrays. */
 
-- 
1.8.1.5

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