linux-kernel - [PATCH v2] rcu: Add necessary WRITE

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Message-Id: <20230620171346.207076-1-mmpgouride@gmail.com>
Date:   Tue, 20 Jun 2023 17:13:46 +0000
From:   Alan Huang <mmpgouride@...il.com>
To:     paulmck@...nel.org
Cc:     rcu@...r.kernel.org, linux-kernel@...r.kernel.org,
        Alan Huang <mmpgouride@...il.com>
Subject: [PATCH v2] rcu: Add necessary WRITE_ONCE()

Commit c54a2744497d("list: Add hlist_unhashed_lockless()") and
commit 860c8802ace1("rcu: Use WRITE_ONCE() for assignments to
->pprev for hlist_nulls") added various WRITE_ONCE() to pair with
the READ_ONCE() in hlist_unhashed_lockless(), but there are still
some places where WRITE_ONCE() was not added, this commit adds that.

Also add WRITE_ONCE() to pair with the READ_ONCE() in hlist_empty().

Signed-off-by: Alan Huang <mmpgouride@...il.com>
---
Changelog:
V1 -> V2: 
  Add WRITE_ONCE in hlist_del_init to pair with READ_ONCE in
  hlist_unhashed_lockless.

 include/linux/list.h          | 9 +++++----
 include/linux/list_nulls.h    | 2 +-
 include/linux/rculist_nulls.h | 2 +-
 3 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/include/linux/list.h b/include/linux/list.h
index ac366958ea..3a29b95bfe 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -912,7 +912,7 @@ static inline void hlist_del(struct hlist_node *n)
 {
 	__hlist_del(n);
 	n->next = LIST_POISON1;
-	n->pprev = LIST_POISON2;
+	WRITE_ONCE(n->pprev, LIST_POISON2);
 }
 
 /**
@@ -925,7 +925,8 @@ static inline void hlist_del_init(struct hlist_node *n)
 {
 	if (!hlist_unhashed(n)) {
 		__hlist_del(n);
-		INIT_HLIST_NODE(n);
+		n->next = NULL;
+		WRITE_ONCE(n->pprev, NULL);
 	}
 }
 
@@ -1026,8 +1027,8 @@ static inline void hlist_move_list(struct hlist_head *old,
 {
 	new->first = old->first;
 	if (new->first)
-		new->first->pprev = &new->first;
-	old->first = NULL;
+		WRITE_ONCE(new->first->pprev, &new->first);
+	WRITE_ONCE(old->first, NULL);
 }
 
 #define hlist_entry(ptr, type, member) container_of(ptr,type,member)
diff --git a/include/linux/list_nulls.h b/include/linux/list_nulls.h
index fa6e8471bd..b63b0589fa 100644
--- a/include/linux/list_nulls.h
+++ b/include/linux/list_nulls.h
@@ -95,7 +95,7 @@ static inline void hlist_nulls_add_head(struct hlist_nulls_node *n,
 
 	n->next = first;
 	WRITE_ONCE(n->pprev, &h->first);
-	h->first = n;
+	WRITE_ONCE(h->first, n);
 	if (!is_a_nulls(first))
 		WRITE_ONCE(first->pprev, &n->next);
 }
diff --git a/include/linux/rculist_nulls.h b/include/linux/rculist_nulls.h
index ba4c00dd80..c65121655b 100644
--- a/include/linux/rculist_nulls.h
+++ b/include/linux/rculist_nulls.h
@@ -138,7 +138,7 @@ static inline void hlist_nulls_add_tail_rcu(struct hlist_nulls_node *n,
 
 	if (last) {
 		n->next = last->next;
-		n->pprev = &last->next;
+		WRITE_ONCE(n->pprev, &last->next);
 		rcu_assign_pointer(hlist_nulls_next_rcu(last), n);
 	} else {
 		hlist_nulls_add_head_rcu(n, h);
-- 
2.34.1