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authorpierre Kuo <vichy.kuo@gmail.com>2017-04-07 14:37:36 +0800
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2017-04-12 08:23:43 -0700
commitb26cfc48e3e03126c183f1f3960e6d69460bb852 (patch)
treeea7929ee20ba916595758350c958d1d81594d1e6
parentdoc: Emphasize that "toy" RCU requires recursive rwlock (diff)
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doc: Update control-dependencies section of memory-barriers.txt
In the following example, if MAX is defined to be 1, then the compiler knows (Q % MAX) is equal to zero. The compiler can therefore throw away the "then" branch (and the "if"), retaining only the "else" branch. q = READ_ONCE(a); if (q % MAX) { WRITE_ONCE(b, 1); do_something(); } else { WRITE_ONCE(b, 2); do_something_else(); } It is therefore necessary to modify the example like this: q = READ_ONCE(a); - WRITE_ONCE(b, 1); + WRITE_ONCE(b, 2); do_something_else(); Signed-off-by: pierre Kuo <vichy.kuo@gmail.com> Acked-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
-rw-r--r--Documentation/memory-barriers.txt2
1 files changed, 1 insertions, 1 deletions
diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
index d2b0a8d81258..08329cb857ed 100644
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -768,7 +768,7 @@ equal to zero, in which case the compiler is within its rights to
transform the above code into the following:
q = READ_ONCE(a);
- WRITE_ONCE(b, 1);
+ WRITE_ONCE(b, 2);
do_something_else();
Given this transformation, the CPU is not required to respect the ordering