linux-kernel - [PATCH tip/core/rcu 7/8] rcu: Add sparse check to rcu_assign

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Date:   Wed,  9 Jan 2019 13:41:41 -0800
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     linux-kernel@...r.kernel.org
Cc:     mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
        fweisbec@...il.com, oleg@...hat.com, joel@...lfernandes.org,
        "Paul E . McKenney" <paulmck@...ux.ibm.com>
Subject: [PATCH tip/core/rcu 7/8] rcu: Add sparse check to rcu_assign_pointer()

From: "Joel Fernandes (Google)" <joel@...lfernandes.org>

The rcu_assign_pointer() function currently doesn't do any sparse checking
on the assigned-to pointer.  So its possible that a pointer that is
not __rcu annotated is assigned with rcu_assign_pointer without sparse
complaints.  Because rcu_dereference() already does such checking,
this commit makes rcu_assign_pointer() to do the same. The extra
error could be helpful in cases where an RCU pointer is assigned with
rcu_assign_pointer() but not annotated with __rcu.

This doesn't generate any code in the normal case because __CHECKER__ is
defined only in the context of sparse.

This commit also renames rcu_dereference_sparse() to rcu_check_parse()
since the checking now happens not only during derereferencing but also
during assignment.

Test: Introduced an rcu_assign_pointer in code and checked the output of
sparse with and without this change. The change correctly causes sparse
to throw an error.

Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@...ux.ibm.com>
---
 include/linux/rcupdate.h | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index b4e99639d6d4..0bb5d906bff3 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -309,16 +309,16 @@ static inline void rcu_preempt_sleep_check(void) { }
  */
 
 #ifdef __CHECKER__
-#define rcu_dereference_sparse(p, space) \
+#define rcu_check_sparse(p, space) \
 	((void)(((typeof(*p) space *)p) == p))
 #else /* #ifdef __CHECKER__ */
-#define rcu_dereference_sparse(p, space)
+#define rcu_check_sparse(p, space)
 #endif /* #else #ifdef __CHECKER__ */
 
 #define __rcu_access_pointer(p, space) \
 ({ \
 	typeof(*p) *_________p1 = (typeof(*p) *__force)READ_ONCE(p); \
-	rcu_dereference_sparse(p, space); \
+	rcu_check_sparse(p, space); \
 	((typeof(*p) __force __kernel *)(_________p1)); \
 })
 #define __rcu_dereference_check(p, c, space) \
@@ -326,13 +326,13 @@ static inline void rcu_preempt_sleep_check(void) { }
 	/* Dependency order vs. p above. */ \
 	typeof(*p) *________p1 = (typeof(*p) *__force)READ_ONCE(p); \
 	RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \
-	rcu_dereference_sparse(p, space); \
+	rcu_check_sparse(p, space); \
 	((typeof(*p) __force __kernel *)(________p1)); \
 })
 #define __rcu_dereference_protected(p, c, space) \
 ({ \
 	RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \
-	rcu_dereference_sparse(p, space); \
+	rcu_check_sparse(p, space); \
 	((typeof(*p) __force __kernel *)(p)); \
 })
 #define rcu_dereference_raw(p) \
@@ -382,6 +382,7 @@ static inline void rcu_preempt_sleep_check(void) { }
 #define rcu_assign_pointer(p, v)					      \
 ({									      \
 	uintptr_t _r_a_p__v = (uintptr_t)(v);				      \
+	rcu_check_sparse(p, __rcu);				      \
 									      \
 	if (__builtin_constant_p(v) && (_r_a_p__v) == (uintptr_t)NULL)	      \
 		WRITE_ONCE((p), (typeof(p))(_r_a_p__v));		      \
@@ -785,7 +786,7 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
  */
 #define RCU_INIT_POINTER(p, v) \
 	do { \
-		rcu_dereference_sparse(p, __rcu); \
+		rcu_check_sparse(p, __rcu); \
 		WRITE_ONCE(p, RCU_INITIALIZER(v)); \
 	} while (0)
 
-- 
2.17.1