[tip:core/locking] futexes: Fix futex_hashsize initialization

From: tip-bot for Heiko Carstens
Date: Thu Jan 16 2014 - 09:19:14 EST

Commit-ID: 63b1a81699c2a45c9f737419b1ec1da0ecf92812
Gitweb: http://git.kernel.org/tip/63b1a81699c2a45c9f737419b1ec1da0ecf92812
Author: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
AuthorDate: Thu, 16 Jan 2014 14:54:50 +0100
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Thu, 16 Jan 2014 15:14:32 +0100

futexes: 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@xxxxxxxxxx>
Cc: Darren Hart <dvhart@xxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Waiman Long <Waiman.Long@xxxxxx>
Cc: Jason Low <jason.low2@xxxxxx>
Cc: Davidlohr Bueso <davidlohr@xxxxxx>
Link: 20140116135450.GA4345@osiris">http://lkml.kernel.org/r/20140116135450.GA4345@osiris
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
kernel/futex.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index 30971b5..1ddc449 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2844,6 +2844,7 @@ 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;

@@ -2855,8 +2856,9 @@ 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()
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