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author | Eric Paris <eparis@redhat.com> | 2009-03-23 18:22:09 +0100 |
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committer | Ingo Molnar <mingo@elte.hu> | 2009-04-29 16:45:54 +0200 |
commit | b1fca26631f76a5e8b18435a43f5d82b8734da4b (patch) | |
tree | 6b8e651239219e85a6b3b9238878c4a6eb4f2d9c /include | |
parent | 56a50adda49b2020156616c4eb15353e0f9ad7de (diff) | |
download | linux-stable-b1fca26631f76a5e8b18435a43f5d82b8734da4b.tar.gz linux-stable-b1fca26631f76a5e8b18435a43f5d82b8734da4b.tar.bz2 linux-stable-b1fca26631f76a5e8b18435a43f5d82b8734da4b.zip |
mutex: add atomic_dec_and_mutex_lock()
Much like the atomic_dec_and_lock() function in which we take an hold a
spin_lock if we drop the atomic to 0 this function takes and holds the
mutex if we dec the atomic to 0.
Signed-off-by: Eric Paris <eparis@redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Orig-LKML-Reference: <20090323172417.410913479@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'include')
-rw-r--r-- | include/linux/mutex.h | 23 |
1 files changed, 23 insertions, 0 deletions
diff --git a/include/linux/mutex.h b/include/linux/mutex.h index 3069ec7e0ab8..93054fc3635c 100644 --- a/include/linux/mutex.h +++ b/include/linux/mutex.h @@ -151,4 +151,27 @@ extern int __must_check mutex_lock_killable(struct mutex *lock); extern int mutex_trylock(struct mutex *lock); extern void mutex_unlock(struct mutex *lock); +/** + * atomic_dec_and_mutex_lock - return holding mutex if we dec to 0 + * @cnt: the atomic which we are to dec + * @lock: the mutex to return holding if we dec to 0 + * + * return true and hold lock if we dec to 0, return false otherwise + */ +static inline int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock) +{ + /* dec if we can't possibly hit 0 */ + if (atomic_add_unless(cnt, -1, 1)) + return 0; + /* we might hit 0, so take the lock */ + mutex_lock(lock); + if (!atomic_dec_and_test(cnt)) { + /* when we actually did the dec, we didn't hit 0 */ + mutex_unlock(lock); + return 0; + } + /* we hit 0, and we hold the lock */ + return 1; +} + #endif |