linux-kernel - [PATCH V2] futex: fix compiler warnings in exit_robust

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Date:	Thu,  4 Nov 2010 15:00:00 -0400
From:	Darren Hart <dvhart@...ux.intel.com>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc:	Darren Hart <dvhart@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Eric Dumazet <eric.dumazet@...il.com>,
	John Kacur <jkacur@...hat.com>
Subject: [PATCH V2] futex: fix compiler warnings in exit_robust_list

The following commit introduced a compiler warning:

Commit 1dcc41bb037533839753df983d31778b30b67d93
futex: Change 3rd arg of fetch_robust_entry() to unsigned int*

The following archs/compiler versions all report:
kernel/futex.c: In function ‘exit_robust_list’:
kernel/futex.c:2492: warning: ‘next_pi’ may be used uninitialized in this function

x86_64
gcc (Ubuntu 4.4.3-4ubuntu5) 4.4.3
gcc (GCC) 4.4.4 20100630 (Red Hat 4.4.4-10)
gcc (Ubuntu/Linaro 4.4.4-14ubuntu5) 4.4.5

sh
sh-linux-gnu-gcc (Sourcery G++ Lite 4.3-143) 4.3.3

arm
arm-1136jfs-linux-gnueabi-gcc (OSELAS.Toolchain-1.99.3) 4.3.2

The code path really can't result in next_pi being unitialized (or should
not), but let's keep the build clean. Annotate next_pi as an uninitialized_var.

V2: Implement Uwe's suggestion to use uninitialized_var()

Signed-off-by: Darren Hart <dvhart@...ux.intel.com>
Tested-by: Matt Fleming <matt@...sole-pimps.org>
Tested-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...e.hu>
CC: Eric Dumazet <eric.dumazet@...il.com>
CC: John Kacur <jkacur@...hat.com>
---
 kernel/futex.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index 6c683b3..40a8777 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2489,7 +2489,8 @@ void exit_robust_list(struct task_struct *curr)
 {
 	struct robust_list_head __user *head = curr->robust_list;
 	struct robust_list __user *entry, *next_entry, *pending;
-	unsigned int limit = ROBUST_LIST_LIMIT, pi, next_pi, pip;
+	unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
+	unsigned int uninitialized_var(next_pi);
 	unsigned long futex_offset;
 	int rc;
 
-- 
1.7.1

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