documentation: State that rcu_dereference() reloads pointer

Make a note stating that repeated calls of rcu_dereference() may not
return the same pointer if update happens while in critical section.

Reported-by: Jeff Haran <jeff.haran@citrix.com>
Signed-off-by: Milos Vyletel <milos@redhat.com>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt
index 88dfce1..16622c9 100644 (file)
--- a/Documentation/RCU/whatisRCU.txt
+++ b/Documentation/RCU/whatisRCU.txt
@@ -256,7 +256,9 @@ rcu_dereference()
        If you are going to be fetching multiple fields from the
        RCU-protected structure, using the local variable is of
        course preferred.  Repeated rcu_dereference() calls look
-       ugly and incur unnecessary overhead on Alpha CPUs.
+       ugly, do not guarantee that the same pointer will be returned
+       if an update happened while in the critical section, and incur
+       unnecessary overhead on Alpha CPUs.
 
        Note that the value returned by rcu_dereference() is valid
        only within the enclosing RCU read-side critical section.