diff options
| author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2014-08-04 11:49:34 -0700 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2014-09-07 16:15:52 -0700 |
| commit | efdcd51a4d5bd355796b1a757ff0355bb09ed394 (patch) | |
| tree | c8b39a7b01980753ff864c7a28bc9ac0ae180701 | |
| parent | 5646f7acc95f14873f1ec715380c1c493b4243ce (diff) | |
memory-barriers: Retain barrier() in fold-to-zero example
The transformation in the fold-to-zero example incorrectly omits the
barrier() directive. This commit therefore adds it back in.
Reported-by: Pranith Kumar <pranith@gatech.edu>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| -rw-r--r-- | Documentation/memory-barriers.txt | 9 |
1 files changed, 6 insertions, 3 deletions
diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt index d67c508eb660..600b45c6e2ad 100644 --- a/Documentation/memory-barriers.txt +++ b/Documentation/memory-barriers.txt @@ -679,12 +679,15 @@ equal to zero, in which case the compiler is within its rights to transform the above code into the following: q = ACCESS_ONCE(a); + barrier(); ACCESS_ONCE(b) = p; do_something_else(); -This transformation loses the ordering between the load from variable 'a' -and the store to variable 'b'. If you are relying on this ordering, you -should do something like the following: +This transformation fails to require that the CPU respect the ordering +between the load from variable 'a' and the store to variable 'b'. +Yes, the barrier() is still there, but it affects only the compiler, +not the CPU. Therefore, if you are relying on this ordering, you should +do something like the following: q = ACCESS_ONCE(a); BUILD_BUG_ON(MAX <= 1); /* Order load from a with store to b. */ |