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| -rw-r--r-- | Documentation/memory-barriers.txt | 10 |
1 files changed, 7 insertions, 3 deletions
diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt index 904ee42d078e..e26058d3e253 100644 --- a/Documentation/memory-barriers.txt +++ b/Documentation/memory-barriers.txt @@ -800,9 +800,13 @@ In summary: use smp_rmb(), smp_wmb(), or, in the case of prior stores and later loads, smp_mb(). - (*) If both legs of the "if" statement begin with identical stores - to the same variable, a barrier() statement is required at the - beginning of each leg of the "if" statement. + (*) If both legs of the "if" statement begin with identical stores to + 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. (*) Control dependencies require at least one run-time conditional between the prior load and the subsequent store, and this |