Commit-ID: 96d7744e0a5631a1b5fef2a97658150b165f02b6 Gitweb: http://git.kernel.org/tip/96d7744e0a5631a1b5fef2a97658150b165f02b6 Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> AuthorDate: Mon, 13 Jul 2015 15:55:52 -0700 Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> CommitDate: Wed, 15 Jul 2015 14:43:14 -0700 doc: Call out smp_mb__after_unlock_lock() transitivity Although "full barrier" should be interpreted as providing transitivity, it is worth eliminating any possible confusion. This commit therefore adds "(including transitivity)" to eliminate any possible confusion. Reported-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> --- Documentation/memory-barriers.txt | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt index 470c07c..3185238 100644 --- a/Documentation/memory-barriers.txt +++ b/Documentation/memory-barriers.txt @@ -1858,11 +1858,12 @@ Similarly, the reverse case of a RELEASE followed by an ACQUIRE does not imply a full memory barrier. If it is necessary for a RELEASE-ACQUIRE pair to produce a full barrier, the ACQUIRE can be followed by an smp_mb__after_unlock_lock() invocation. This will produce a full barrier -if either (a) the RELEASE and the ACQUIRE are executed by the same -CPU or task, or (b) the RELEASE and ACQUIRE act on the same variable. -The smp_mb__after_unlock_lock() primitive is free on many architectures. -Without smp_mb__after_unlock_lock(), the CPU's execution of the critical -sections corresponding to the RELEASE and the ACQUIRE can cross, so that: +(including transitivity) if either (a) the RELEASE and the ACQUIRE are +executed by the same CPU or task, or (b) the RELEASE and ACQUIRE act on +the same variable. The smp_mb__after_unlock_lock() primitive is free +on many architectures. Without smp_mb__after_unlock_lock(), the CPU's +execution of the critical sections corresponding to the RELEASE and the +ACQUIRE can cross, so that: *A = a; RELEASE M -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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