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s390: spinlock corner case.

PATCH New Martin Schwidefsky 1 participant 1 message Aug 29, 2005

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Martin Schwidefsky

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PATCH 9/10 s390: spinlock corner case.

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

From: Heiko Carstens <[email protected]>

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 <[email protected]>
Signed-off-by Martin Schwidefsky <[email protected]>

diffstat:

 include/asm-s390/spinlock.h |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
include/asm-s390/spinlock.h +2 -2
diff -urpN linux-2.6/include/asm-s390/spinlock.h linux-2.6-patched/include/asm-s390/spinlock.h
@@ -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;