linux-kernel - [PATCH v1] timerqueue: use rb_entry_safe() in timerqueue

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Date:   Thu, 27 Oct 2022 21:37:07 +0000
From:   Barnabás Pőcze <pobrn@...tonmail.com>
To:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH v1] timerqueue: use rb_entry_safe() in timerqueue_getnext()

When `timerqueue_getnext()` is called on an empty timerqueue
the returned rb_node pointer will be NULL. Using `rb_entry()`
on a potentially NULL pointer will only - coincidentally - work
if the offset of the rb_node member is 0. This is currently the
case for `timerqueue_node`, but should this ever change,
`timerqueue_getnext()` will no longer work correctly on empty
timerqueues. To avoid this, switch to using `rb_entry_safe()`.

Signed-off-by: Barnabás Pőcze <pobrn@...tonmail.com>
---
 include/linux/timerqueue.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/timerqueue.h b/include/linux/timerqueue.h
index 93884086f392..adc80e29168e 100644
--- a/include/linux/timerqueue.h
+++ b/include/linux/timerqueue.h
@@ -35,7 +35,7 @@ struct timerqueue_node *timerqueue_getnext(struct timerqueue_head *head)
 {
 	struct rb_node *leftmost = rb_first_cached(&head->rb_root);

-	return rb_entry(leftmost, struct timerqueue_node, node);
+	return rb_entry_safe(leftmost, struct timerqueue_node, node);
 }

 static inline void timerqueue_init(struct timerqueue_node *node)
--
2.38.1