diff options
Diffstat (limited to 'kernel/Documentation/atomic_ops.txt')
| -rw-r--r-- | kernel/Documentation/atomic_ops.txt | 8 |
1 files changed, 7 insertions, 1 deletions
diff --git a/kernel/Documentation/atomic_ops.txt b/kernel/Documentation/atomic_ops.txt index dab6da338..c9d1cacb4 100644 --- a/kernel/Documentation/atomic_ops.txt +++ b/kernel/Documentation/atomic_ops.txt @@ -266,7 +266,9 @@ with the given old and new values. Like all atomic_xxx operations, atomic_cmpxchg will only satisfy its atomicity semantics as long as all other accesses of *v are performed through atomic_xxx operations. -atomic_cmpxchg must provide explicit memory barriers around the operation. +atomic_cmpxchg must provide explicit memory barriers around the operation, +although if the comparison fails then no memory ordering guarantees are +required. The semantics for atomic_cmpxchg are the same as those defined for 'cas' below. @@ -540,6 +542,10 @@ The routines xchg() and cmpxchg() must provide the same exact memory-barrier semantics as the atomic and bit operations returning values. +Note: If someone wants to use xchg(), cmpxchg() and their variants, +linux/atomic.h should be included rather than asm/cmpxchg.h, unless +the code is in arch/* and can take care of itself. + Spinlocks and rwlocks have memory barrier expectations as well. The rule to follow is simple: |