X-Git-Url: https://gerrit.opnfv.org/gerrit/gitweb?a=blobdiff_plain;f=kernel%2FDocumentation%2Fatomic_ops.txt;h=c9d1cacb439590a02dbfb1282cbe0d3abe3a9b0d;hb=e09b41010ba33a20a87472ee821fa407a5b8da36;hp=dab6da3382d9f0b5f3c1e9f6e3fafc0cc2535de2;hpb=f93b97fd65072de626c074dbe099a1fff05ce060;p=kvmfornfv.git

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: