On Fri, Aug 22, 2014 at 04:26:05PM +0300, Andreea-Cristina Bernat wrote: > The use of "rcu_assign_pointer()" is NULLing out the pointer. > According to RCU_INIT_POINTER()'s block comment: > "1. This use of RCU_INIT_POINTER() is NULLing out the pointer" > it is better to use it instead of rcu_assign_pointer() because it has a > smaller overhead. > > The following Coccinelle semantic patch was used: > @@ > @@ > > - rcu_assign_pointer > + RCU_INIT_POINTER > (..., NULL) > > Signed-off-by: Andreea-Cristina Bernat <bernat....@gmail.com> > --- > kernel/events/core.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/events/core.c b/kernel/events/core.c > index 0d735be..4b84dd5 100644 > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -5744,7 +5744,7 @@ static void swevent_hlist_release(struct swevent_htable > *swhash) > if (!hlist) > return; > > - rcu_assign_pointer(swhash->swevent_hlist, NULL); > + RCU_INIT_POINTER(swhash->swevent_hlist, NULL); > kfree_rcu(hlist, rcu_head); > }
Paul, why not do something like the below and do away with all this
nonsense?
---
include/linux/rcupdate.h | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index d231aa17b1d7..38c3e629ae70 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -623,7 +623,13 @@ static inline void rcu_preempt_sleep_check(void)
* please be careful when making changes to rcu_assign_pointer() and the
* other macros that it invokes.
*/
-#define rcu_assign_pointer(p, v) smp_store_release(&p, RCU_INITIALIZER(v))
+#define rcu_assign_pointer(p, v) \
+do { \
+ if (__builtin_constant_p(v) && v == NULL) \
+ p = RCU_INITIALIZER(v); \
+ else \
+ smp_store_release(&p, RCU_INITIALIZER(v)); \
+} while (0)
/**
* rcu_access_pointer() - fetch RCU pointer with no dereferencing
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