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| author | Jan Blunck <jblunck@suse.de> | 2009-06-16 15:33:33 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2009-06-16 19:47:47 -0700 |
| commit | 417dcdf99ec9f8d8d6917189130bdc17cb67c678 (patch) | |
| tree | 4a97ab3ec286dda502ee7b3a16e0b6186cdc30d9 | |
| parent | a7d932af06e8eee2163627d19898e18da5635449 (diff) | |
| download | lwn-417dcdf99ec9f8d8d6917189130bdc17cb67c678.tar.gz lwn-417dcdf99ec9f8d8d6917189130bdc17cb67c678.zip | |
atomic: only take lock when the counter drops to zero on UP as well
_atomic_dec_and_lock() should not unconditionally take the lock before
calling atomic_dec_and_test() in the UP case. For consistency reasons it
should behave exactly like in the SMP case.
Besides that this works around the problem that with CONFIG_DEBUG_SPINLOCK
this spins in __spin_lock_debug() if the lock is already taken even if the
counter doesn't drop to 0.
Signed-off-by: Jan Blunck <jblunck@suse.de>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Nick Piggin <npiggin@suse.de>
Cc: Valerie Aurora <vaurora@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
| -rw-r--r-- | lib/dec_and_lock.c | 3 |
1 files changed, 1 insertions, 2 deletions
diff --git a/lib/dec_and_lock.c b/lib/dec_and_lock.c index a65c31455541..e73822aa6e9a 100644 --- a/lib/dec_and_lock.c +++ b/lib/dec_and_lock.c @@ -19,11 +19,10 @@ */ int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock) { -#ifdef CONFIG_SMP /* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */ if (atomic_add_unless(atomic, -1, 1)) return 0; -#endif + /* Otherwise do it the slow way */ spin_lock(lock); if (atomic_dec_and_test(atomic)) |