| From | "Paul E. McKenney" <> | Subject | [PATCH tip/core/rcu 32/55] rcu: Make rcu_assign_pointer() unconditionally insert a memory barrier | Date | Tue, 6 Sep 2011 11:00:26 -0700 |
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From: Eric Dumazet <eric.dumazet@gmail.com>
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> --- include/linux/rcupdate.h | 4 +--- 1 files changed, 1 insertions(+), 3 deletions(-)
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index ea80396..b2e5fe8 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); \ }) -- 1.7.3.2
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