Gitweb:
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=02c608c1fefe821a4c6fc34c45a0dea3cebf4764
Commit: 02c608c1fefe821a4c6fc34c45a0dea3cebf4764
Parent: 2dda81ca31dc73e695ff8b83351f7aaefbef192a
Author: Oleg Nesterov <[EMAIL PROTECTED]>
AuthorDate: Sun Feb 24 00:03:29 2008 +0300
Committer: Linus Torvalds <[EMAIL PROTECTED]>
CommitDate: Sat Feb 23 17:52:36 2008 -0800
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 <[EMAIL PROTECTED]>
Acked-by: Nick Piggin <[EMAIL PROTECTED]>
Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
---
Documentation/atomic_ops.txt | 3 ++-
Documentation/memory-barriers.txt | 2 +-
2 files changed, 3 insertions(+), 2 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)
diff --git a/Documentation/memory-barriers.txt
b/Documentation/memory-barriers.txt
index 4e17beb..1f506f7 100644
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -1493,7 +1493,7 @@ explicit lock operations, described later). These
include:
atomic_dec_and_test();
atomic_sub_and_test();
atomic_add_negative();
- atomic_add_unless();
+ atomic_add_unless(); /* when succeeds (returns 1) */
test_and_set_bit();
test_and_clear_bit();
test_and_change_bit();
-
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