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| -rw-r--r-- | Documentation/memory-barriers.txt | 7 |
1 files changed, 4 insertions, 3 deletions
diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt index 3729cbe60e41..ec1289042396 100644 --- a/Documentation/memory-barriers.txt +++ b/Documentation/memory-barriers.txt @@ -813,9 +813,10 @@ In summary: the same variable, then those stores must be ordered, either by preceding both of them with smp_mb() or by using smp_store_release() to carry out the stores. Please note that it is -not- sufficient - to use barrier() at beginning of each leg of the "if" statement, - as optimizing compilers do not necessarily respect barrier() - in this case. + to use barrier() at beginning of each leg of the "if" statement + because, as shown by the example above, optimizing compilers can + destroy the control dependency while respecting the letter of the + barrier() law. (*) Control dependencies require at least one run-time conditional between the prior load and the subsequent store, and this |