linux-kernel - [RFC PATCH] rcu: rcupdate.h: Add missing parentheses around macro pointer dereference

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Message-Id: <20230503203236.1587590-1-mathieu.desnoyers@efficios.com>
Date:   Wed,  3 May 2023 16:32:36 -0400
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Josh Triplett <josh@...htriplett.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Zqiang <qiang1.zhang@...el.com>
Subject: [RFC PATCH] rcu: rcupdate.h: Add missing parentheses around macro pointer dereference

linux/rcupdate.h macros use the *p parameter without parentheses, e.g.:

  typeof(*p)

rather than

  typeof(*(p))

The following test-case shows how it can generate confusion due to C
operator precedence being reversed compared to the expectations:

    #define m(p) \
    do { \
            __typeof__(*p) v = 0; \
    } while (0)

    void fct(unsigned long long *p1)
    {
            m(p1 + 1);      /* works */
            m(1 + p1);      /* broken */
    }

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: "Paul E. McKenney" <paulmck@...nel.org>
Cc: Joel Fernandes <joel@...lfernandes.org>
Cc: Josh Triplett <josh@...htriplett.org>
Cc: Boqun Feng <boqun.feng@...il.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Lai Jiangshan <jiangshanlai@...il.com>
Cc: Zqiang <qiang1.zhang@...el.com>
---
 include/linux/rcupdate.h | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index dcd2cf1e8326..1565012fa47f 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -430,16 +430,16 @@ static inline void rcu_preempt_sleep_check(void) { }
 
 #ifdef __CHECKER__
 #define rcu_check_sparse(p, space) \
-	((void)(((typeof(*p) space *)p) == p))
+	((void)(((typeof(*(p)) space *)p) == p))
 #else /* #ifdef __CHECKER__ */
 #define rcu_check_sparse(p, space)
 #endif /* #else #ifdef __CHECKER__ */
 
 #define __unrcu_pointer(p, local)					\
 ({									\
-	typeof(*p) *local = (typeof(*p) *__force)(p);			\
+	typeof(*(p)) *local = (typeof(*(p)) *__force)(p);		\
 	rcu_check_sparse(p, __rcu);					\
-	((typeof(*p) __force __kernel *)(local)); 			\
+	((typeof(*(p)) __force __kernel *)(local));			\
 })
 /**
  * unrcu_pointer - mark a pointer as not being RCU protected
@@ -452,29 +452,29 @@ static inline void rcu_preempt_sleep_check(void) { }
 
 #define __rcu_access_pointer(p, local, space) \
 ({ \
-	typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \
+	typeof(*(p)) *local = (typeof(*(p)) *__force)READ_ONCE(p); \
 	rcu_check_sparse(p, space); \
-	((typeof(*p) __force __kernel *)(local)); \
+	((typeof(*(p)) __force __kernel *)(local)); \
 })
 #define __rcu_dereference_check(p, local, c, space) \
 ({ \
 	/* Dependency order vs. p above. */ \
-	typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \
+	typeof(*(p)) *local = (typeof(*(p)) *__force)READ_ONCE(p); \
 	RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \
 	rcu_check_sparse(p, space); \
-	((typeof(*p) __force __kernel *)(local)); \
+	((typeof(*(p)) __force __kernel *)(local)); \
 })
 #define __rcu_dereference_protected(p, local, c, space) \
 ({ \
 	RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \
 	rcu_check_sparse(p, space); \
-	((typeof(*p) __force __kernel *)(p)); \
+	((typeof(*(p)) __force __kernel *)(p)); \
 })
 #define __rcu_dereference_raw(p, local) \
 ({ \
 	/* Dependency order vs. p above. */ \
 	typeof(p) local = READ_ONCE(p); \
-	((typeof(*p) __force __kernel *)(local)); \
+	((typeof(*(p)) __force __kernel *)(local)); \
 })
 #define rcu_dereference_raw(p) __rcu_dereference_raw(p, __UNIQUE_ID(rcu))
 
-- 
2.25.1