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futex: fix futex_hashsize initialization

PATCH New Heiko Carstens 2 participants 2 messages Jan 16, 2014 Linux-next tree

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Heiko Carstens

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PATCH 1/1 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 <[email protected]>
---
 kernel/futex.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)
kernel/futex.c +4 -2
index 3666aa0017ed..44a1261cb9ff 100644
@@ -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()
Signature · 1 line
1.8.4.5
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#1 lore raw

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

futexes: Fix futex_hashsize initialization
Commit-ID:  63b1a81699c2a45c9f737419b1ec1da0ecf92812
Gitweb:     http://git.kernel.org/tip/63b1a81699c2a45c9f737419b1ec1da0ecf92812
Author:     Heiko Carstens <[email protected]>
AuthorDate: Thu, 16 Jan 2014 14:54:50 +0100
Committer:  Ingo Molnar <[email protected]>
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 <[email protected]>
Cc Darren Hart <[email protected]>
Cc Peter Zijlstra <[email protected]>
Cc Paul E. McKenney <[email protected]>
Cc Waiman Long <[email protected]>
Cc Jason Low <[email protected]>
Cc Davidlohr Bueso <[email protected]>
Link http://lkml.kernel.org/r/20140116135450.GA4345@osiris open here
Signed-off-by Ingo Molnar <[email protected]>
---
 kernel/futex.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)
kernel/futex.c +4 -2
index 30971b5..1ddc449 100644
@@ -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;
 
 #if CONFIG_BASE_SMALL

@@ -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()