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authorEric Dumazet <eric.dumazet@gmail.com>2011-07-31 22:09:25 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2011-09-28 21:38:33 -0700
commitd322f45ceed525daa9401154590bbae3222cfefb (patch)
treef9c2534f0b10d149af2f899ad200125dc29f631b
parent7eb4f4553ceaa6c64da83c8a71d5a991c0188655 (diff)
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rcu: Make rcu_assign_pointer() unconditionally insert a memory barrier
Recent changes to gcc give warning messages on rcu_assign_pointers()'s checks that allow it to determine when it is OK to omit the memory barrier. Stephen Hemminger tried a number of gcc tricks to silence this warning, but #pragmas and CPP macros do not work together in the way that would be required to make this work. However, we now have RCU_INIT_POINTER(), which already omits this memory barrier, and which therefore may be used when assigning NULL to an RCU-protected pointer that is accessible to readers. This commit therefore makes rcu_assign_pointer() unconditionally emit the memory barrier. Reported-by: Stephen Hemminger <shemminger@vyatta.com> Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com> Acked-by: David S. Miller <davem@davemloft.net> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
-rw-r--r--include/linux/rcupdate.h4
1 files changed, 1 insertions, 3 deletions
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index caf22e84a743..d7accc5f8892 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -443,9 +443,7 @@ extern int rcu_my_thread_group_empty(void);
})
#define __rcu_assign_pointer(p, v, space) \
({ \
- if (!__builtin_constant_p(v) || \
- ((v) != NULL)) \
- smp_wmb(); \
+ smp_wmb(); \
(p) = (typeof(*v) __force space *)(v); \
})