linux-kernel - [RFC PATCH 3/4] rculist.h: Fix parentheses around macro pointer parameter use

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Date:   Wed,  3 May 2023 21:29:13 -0400
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.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>, rcu@...r.kernel.org
Subject: [RFC PATCH 3/4] rculist.h: Fix parentheses around macro pointer parameter use

Add missing parentheses around use of macro argument "pos" in those
patterns to ensure operator precedence behaves as expected:

- typeof(*pos)
- pos->member

This corrects the following usage pattern where operator precedence is
unexpected:

  LIST_HEAD(testlist);

  struct test {
          struct list_head node;
          int a;
  };

  // pos->member issue
  void f(void)
  {
          struct test *t1;
          struct test **t2 = &t1;

          list_for_each_entry_rcu((*t2), &testlist, node) {       /* works */
                  //...
          }
          list_for_each_entry_rcu(*t2, &testlist, node) { /* broken */
                  //...
          }
  }

The typeof(*pos) lack of parentheses around "pos" is not an issue per se
in the specific macros modified here because "pos" is used as an lvalue,
which should prevent use of any operator causing issue. Still add the
extra parentheses for consistency.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: "Paul E. McKenney" <paulmck@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Frederic Weisbecker <frederic@...nel.org>
Cc: Neeraj Upadhyay <quic_neeraju@...cinc.com>
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>
Cc: rcu@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
---
 include/linux/rculist.h | 28 ++++++++++++++--------------
 1 file changed, 14 insertions(+), 14 deletions(-)

diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index d29740be4833..d27aeff5447d 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -388,9 +388,9 @@ static inline void list_splice_tail_init_rcu(struct list_head *list,
  */
 #define list_for_each_entry_rcu(pos, head, member, cond...)		\
 	for (__list_check_rcu(dummy, ## cond, 0),			\
-	     pos = list_entry_rcu((head)->next, typeof(*pos), member);	\
-		&pos->member != (head);					\
-		pos = list_entry_rcu(pos->member.next, typeof(*pos), member))
+	     pos = list_entry_rcu((head)->next, typeof(*(pos)), member);\
+		&(pos)->member != (head);				\
+		pos = list_entry_rcu((pos)->member.next, typeof(*(pos)), member))
 
 /**
  * list_for_each_entry_srcu	-	iterate over rcu list of given type
@@ -407,9 +407,9 @@ static inline void list_splice_tail_init_rcu(struct list_head *list,
  */
 #define list_for_each_entry_srcu(pos, head, member, cond)		\
 	for (__list_check_srcu(cond),					\
-	     pos = list_entry_rcu((head)->next, typeof(*pos), member);	\
-		&pos->member != (head);					\
-		pos = list_entry_rcu(pos->member.next, typeof(*pos), member))
+	     pos = list_entry_rcu((head)->next, typeof(*(pos)), member);\
+		&(pos)->member != (head);				\
+		pos = list_entry_rcu((pos)->member.next, typeof(*(pos)), member))
 
 /**
  * list_entry_lockless - get the struct for this entry
@@ -441,9 +441,9 @@ static inline void list_splice_tail_init_rcu(struct list_head *list,
  * but never deleted.
  */
 #define list_for_each_entry_lockless(pos, head, member) \
-	for (pos = list_entry_lockless((head)->next, typeof(*pos), member); \
-	     &pos->member != (head); \
-	     pos = list_entry_lockless(pos->member.next, typeof(*pos), member))
+	for (pos = list_entry_lockless((head)->next, typeof(*(pos)), member); \
+	     &(pos)->member != (head); \
+	     pos = list_entry_lockless((pos)->member.next, typeof(*(pos)), member))
 
 /**
  * list_for_each_entry_continue_rcu - continue iteration over list of given type
@@ -464,9 +464,9 @@ static inline void list_splice_tail_init_rcu(struct list_head *list,
  * position.
  */
 #define list_for_each_entry_continue_rcu(pos, head, member) 		\
-	for (pos = list_entry_rcu(pos->member.next, typeof(*pos), member); \
-	     &pos->member != (head);	\
-	     pos = list_entry_rcu(pos->member.next, typeof(*pos), member))
+	for (pos = list_entry_rcu((pos)->member.next, typeof(*(pos)), member); \
+	     &(pos)->member != (head);	\
+	     pos = list_entry_rcu((pos)->member.next, typeof(*(pos)), member))
 
 /**
  * list_for_each_entry_from_rcu - iterate over a list from current point
@@ -486,8 +486,8 @@ static inline void list_splice_tail_init_rcu(struct list_head *list,
  * after the given position.
  */
 #define list_for_each_entry_from_rcu(pos, head, member)			\
-	for (; &(pos)->member != (head);					\
-		pos = list_entry_rcu(pos->member.next, typeof(*(pos)), member))
+	for (; &(pos)->member != (head);				\
+		pos = list_entry_rcu((pos)->member.next, typeof(*(pos)), member))
 
 /**
  * hlist_del_rcu - deletes entry from hash list without re-initialization
-- 
2.25.1