diff options
| author | Shaohua Li <shli@kernel.org> | 2012-10-08 16:32:18 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2012-10-09 16:22:46 +0900 |
| commit | e79bee24fd6134f90af4228cfebd010136d67631 (patch) | |
| tree | ecc678106bbf4672becca8f798aaf94276eaa2c4 /include/linux/atomic.h | |
| parent | 435b405c06119d93333738172b8060b0ed12af41 (diff) | |
atomic: implement generic atomic_dec_if_positive()
The x86 implementation of atomic_dec_if_positive is quite generic, so make
it available to all architectures.
This is needed for "swap: add a simple detector for inappropriate swapin
readahead".
[akpm@linux-foundation.org: do the "#define foo foo" trick in the conventional manner]
Signed-off-by: Shaohua Li <shli@fusionio.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Rik van Riel <riel@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Michal Simek <monstr@monstr.eu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include/linux/atomic.h')
| -rw-r--r-- | include/linux/atomic.h | 25 |
1 files changed, 25 insertions, 0 deletions
diff --git a/include/linux/atomic.h b/include/linux/atomic.h index 70cfcb2d63c4..5b08a8540ecf 100644 --- a/include/linux/atomic.h +++ b/include/linux/atomic.h @@ -86,6 +86,31 @@ static inline int atomic_dec_unless_positive(atomic_t *p) } #endif +/* + * atomic_dec_if_positive - decrement by 1 if old value positive + * @v: pointer of type atomic_t + * + * The function returns the old value of *v minus 1, even if + * the atomic variable, v, was not decremented. + */ +#ifndef atomic_dec_if_positive +static inline int atomic_dec_if_positive(atomic_t *v) +{ + int c, old, dec; + c = atomic_read(v); + for (;;) { + dec = c - 1; + if (unlikely(dec < 0)) + break; + old = atomic_cmpxchg((v), c, dec); + if (likely(old == c)) + break; + c = old; + } + return dec; +} +#endif + #ifndef CONFIG_ARCH_HAS_ATOMIC_OR static inline void atomic_or(int i, atomic_t *v) { |