[patch 9/10] s390: spinlock corner case.

[Martin Schwidefsky <schwidefsky@de.ibm.com>]

[patch 9/10] s390: spinlock corner case.

From: Heiko Carstens <heiko.carstens@de.ibm.com>

On s390 the lock value used for spinlocks consists of the lower 32 bits
of the PSW that holds the lock. If this address happens to be on a four
gigabyte boundary the lock is left unlocked. This allows other cpus to
grab the same lock and enter a lock protected code path concurrently.
In theory this can happen if the vmalloc area for the code of a module
crosses a 4 GB boundary.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

diffstat:
 include/asm-s390/spinlock.h |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff -urpN linux-2.6/include/asm-s390/spinlock.h linux-2.6-patched/include/asm-s390/spinlock.h
--- linux-2.6/include/asm-s390/spinlock.h	2005-08-29 01:41:01.000000000 +0200
+++ linux-2.6-patched/include/asm-s390/spinlock.h	2005-08-29 19:18:12.000000000 +0200
@@ -47,7 +47,7 @@ extern int _raw_spin_trylock_retry(spinl
 
 static inline void _raw_spin_lock(spinlock_t *lp)
 {
-	unsigned long pc = (unsigned long) __builtin_return_address(0);
+	unsigned long pc = 1 | (unsigned long) __builtin_return_address(0);
 
 	if (unlikely(_raw_compare_and_swap(&lp->lock, 0, pc) != 0))
 		_raw_spin_lock_wait(lp, pc);
@@ -55,7 +55,7 @@ static inline void _raw_spin_lock(spinlo
 
 static inline int _raw_spin_trylock(spinlock_t *lp)
 {
-	unsigned long pc = (unsigned long) __builtin_return_address(0);
+	unsigned long pc = 1 | (unsigned long) __builtin_return_address(0);
 
 	if (likely(_raw_compare_and_swap(&lp->lock, 0, pc) == 0))
 		return 1;
-
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