[RFC PATCH 1/4] rcu: rcupdate.h: Add missing parentheses around macro pointer dereference

From: Mathieu Desnoyers
Date: Wed May 03 2023 - 21:29:33 EST


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@xxxxxxxxxxxx>
Reviewed-by: Boqun Feng <boqun.feng@xxxxxxxxx>
Reviewed-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Reviewed-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
Cc: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx>
Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Lai Jiangshan <jiangshanlai@xxxxxxxxx>
Cc: Zqiang <qiang1.zhang@xxxxxxxxx>
---
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..38e84f3d515e 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