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| author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2015-07-14 00:55:52 +0200 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2015-07-15 23:43:14 +0200 |
| commit | 96d7744e0a5631a1b5fef2a97658150b165f02b6 (patch) | |
| tree | 659b750951bf907b949ce27758721a84cddb2437 /Documentation/memory-barriers.txt | |
| parent | documentation: Replace ACCESS_ONCE() by READ_ONCE() and WRITE_ONCE() (diff) | |
| download | linux-96d7744e0a5631a1b5fef2a97658150b165f02b6.tar.xz linux-96d7744e0a5631a1b5fef2a97658150b165f02b6.zip | |
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@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'Documentation/memory-barriers.txt')
| -rw-r--r-- | Documentation/memory-barriers.txt | 11 |
1 files changed, 6 insertions, 5 deletions
diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt index 470c07c868e4..318523872db5 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 |