Commit-ID: efdcd51a4d5bd355796b1a757ff0355bb09ed394 Gitweb: http://git.kernel.org/tip/efdcd51a4d5bd355796b1a757ff0355bb09ed394 Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> AuthorDate: Mon, 4 Aug 2014 11:49:34 -0700 Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> CommitDate: Sun, 7 Sep 2014 16:15:52 -0700 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@xxxxxxxxxx> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> --- Documentation/memory-barriers.txt | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt index d67c508..600b45c 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. */ -- 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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