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rcu: No ordering for rcu_assign_pointer() of NULL

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This commit does a compile-time check for rcu_assign_pointer() of NULL,
and uses WRITE_ONCE() rather than smp_store_release() in that case.

Reported-by: Christoph Hellwig <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
This commit is contained in:
Paul E. McKenney committed 2016-06-15 15:31:28 -07:00
1 parent 810ce8b5df
commit 3a37f7275c
1 file changed
+10 -1
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include/linux/rcupdate.h
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@@ -650,7 +650,16 @@ 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) \
({ \
uintptr_t _r_a_p__v = (uintptr_t)(v); \
\
if (__builtin_constant_p(v) && (_r_a_p__v) == (uintptr_t)NULL) \
WRITE_ONCE((p), (typeof(p))(_r_a_p__v)); \
else \
smp_store_release(&p, RCU_INITIALIZER((typeof(p))_r_a_p__v)); \
_r_a_p__v; \
})
/**
* rcu_access_pointer() - fetch RCU pointer with no dereferencing