linux-kernel - [PATCH -next] futex: fix futex

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Date:	Thu, 16 Jan 2014 14:54:50 +0100
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Ingo Molnar <mingo@...e.hu>, Davidlohr Bueso <davidlohr@...com>
Cc:	linux-next@...r.kernel.org, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Darren Hart <dvhart@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Waiman Long <Waiman.Long@...com>, Jason Low <jason.low2@...com>
Subject: [PATCH -next] futex: fix futex_hashsize initialization

"futexes: Increase hash table size for better performance" introduces a new
alloc_large_system_hash() call. alloc_large_system_hash() however may allocate
less memory than requested, e.g. limited by MAX_ORDER.

Hence pass a pointer to alloc_large_system_hash() which will contain the hash
shift when the function returns. Afterwards correctly set futex_hashsize.

Fixes a crash on s390 where the requested allocation size was 4MB but only 1MB
was allocated.

Signed-off-by: Heiko Carstens <heiko.carstens@...ibm.com>
---
 kernel/futex.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index 3666aa0017ed..44a1261cb9ff 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2846,6 +2846,7 @@ SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
 static int __init futex_init(void)
 {
 	u32 curval;
+	unsigned int futex_shift;
 	unsigned long i;
 
 #if CONFIG_BASE_SMALL
@@ -2857,8 +2858,9 @@ static int __init futex_init(void)
 	futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues),
 					       futex_hashsize, 0,
 					       futex_hashsize < 256 ? HASH_SMALL : 0,
-					       NULL, NULL, futex_hashsize, futex_hashsize);
-
+					       &futex_shift, NULL,
+					       futex_hashsize, futex_hashsize);
+	futex_hashsize = 1UL << futex_shift;
 	/*
 	 * This will fail and we want it. Some arch implementations do
 	 * runtime detection of the futex_atomic_cmpxchg_inatomic()
-- 
1.8.4.5

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