[PATCH RFC 02/16] rcu: Mark __rcu_access_pointer() as context_unsafe()

["Paul E. McKenney" <paulmck@kernel.org>]

A simple comparison of a pointer returned by rcu_access_pointer() results
in a context-analysis warning for lockless inspection of the RCU-protected
(also known as __rcu-protected) pointer.  This can be suppressed by
placing context_unsafe() calls around calls rcu_access_pointer(),
but this is messy and distracting.  This commit therefore wraps the
underlying __rcu_access_pointer() macro with a call to context_unsafe(),
thereby informing the context-analysis code that rcu_access_pointer()
may safely be invoked outside of an RCU read-side critical section.

Reported-by: Christoph Hellwig <hch@lst.de>
Suggested-by: Marco Elver <elver@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Tested-by: Nilay Shroff <nilay@linux.ibm.com>
Reviewed-by: Marco Elver <elver@google.com>
---
 include/linux/rcupdate.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 5e95acc33989b6..e40dc2e20c5b1f 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -490,12 +490,12 @@ context_unsafe(								\
  */
 #define unrcu_pointer(p) __unrcu_pointer(p, __UNIQUE_ID(rcu))
 
-#define __rcu_access_pointer(p, local, space) \
+#define __rcu_access_pointer(p, local, space) context_unsafe( \
 ({ \
 	typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \
 	rcu_check_sparse(p, space); \
 	((typeof(*p) __force __kernel *)(local)); \
-})
+}) )
 #define __rcu_dereference_check(p, local, c, space) \
 ({ \
 	/* Dependency order vs. p above. */ \
-- 
2.40.1