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documentation: Update rcu_dereference.txt based on WG21 discussions 

This commit provides another caveat for the care and feeding of pointers
returned by rcu_dereference() that was pointed out in discussions within
the C++ standards committee.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
This commit is contained in:
Paul E. McKenney 2015-04-07 12:45:41 -07:00
parent d956028e99
commit ee7c29be36
1 changed files with 5 additions and 0 deletions
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Documentation/RCU/rcu_dereference.txt
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@ -193,6 +193,11 @@ o Be very careful about comparing pointers obtained from
pointer. Note that the volatile cast in rcu_dereference()
will normally prevent the compiler from knowing too much.
However, please note that if the compiler knows that the
pointer takes on only one of two values, a not-equal
comparison will provide exactly the information that the
compiler needs to deduce the value of the pointer.
o Disable any value-speculation optimizations that your compiler
might provide, especially if you are making use of feedback-based
optimizations that take data collected from prior runs. Such