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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() pointer. Note that the volatile cast in rcu_dereference()
will normally prevent the compiler from knowing too much. 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 o Disable any value-speculation optimizations that your compiler
might provide, especially if you are making use of feedback-based might provide, especially if you are making use of feedback-based
optimizations that take data collected from prior runs. Such optimizations that take data collected from prior runs. Such