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authorOleg Nesterov <oleg@tv-sign.ru>2008-02-23 21:03:29 (GMT)
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2008-02-24 01:52:36 (GMT)
commit02c608c1fefe821a4c6fc34c45a0dea3cebf4764 (patch)
tree8fd360da8bc83dd45ecec5621791baa73ddfac70 /Documentation/atomic_ops.txt
parent2dda81ca31dc73e695ff8b83351f7aaefbef192a (diff)
documentation: atomic_add_unless() doesn't imply mb() on failure
(sorry for being offtpoic, but while experts are here...) A "typical" implementation of atomic_add_unless() can return 0 immediately after the first atomic_read() (before doing cmpxchg). In that case it doesn't provide any barrier semantics. See include/asm-ia64/atomic.h as an example. We should either change the implementation, or fix the docs. Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Acked-by: Nick Piggin <npiggin@suse.de> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation/atomic_ops.txt')
-rw-r--r--Documentation/atomic_ops.txt3
1 files changed, 2 insertions, 1 deletions
diff --git a/Documentation/atomic_ops.txt b/Documentation/atomic_ops.txt
index f20c10c..4ef2450 100644
--- a/Documentation/atomic_ops.txt
+++ b/Documentation/atomic_ops.txt
@@ -186,7 +186,8 @@ If the atomic value v is not equal to u, this function adds a to v, and
returns non zero. If v is equal to u then it returns zero. This is done as
an atomic operation.
-atomic_add_unless requires explicit memory barriers around the operation.
+atomic_add_unless requires explicit memory barriers around the operation
+unless it fails (returns 0).
atomic_inc_not_zero, equivalent to atomic_add_unless(v, 1, 0)

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