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Message-ID: <20240610124406.484973160@linutronix.de>
Date: Mon, 10 Jun 2024 14:46:37 +0200 (CEST)
From: Thomas Gleixner <tglx@...utronix.de>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Steven Rostedt <rostedt@...dmis.org>,
Sam Sun <samsun1006219@...il.com>,
x86@...nel.org,
syzkaller-bugs@...glegroups.com,
xrivendell7@...il.com
Subject: [patch 3/4] jump_label: Clarify condition in
static_key_fast_inc_not_disabled()
The second part of
if (v <= 0 || (v + 1) < 0)
is not immediately obvious that it acts as overflow protection.
Check explicitely for v == INT_MAX instead and add a proper comment how
this is used at the call sites.
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
kernel/jump_label.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -132,12 +132,15 @@ bool static_key_fast_inc_not_disabled(st
/*
* Negative key->enabled has a special meaning: it sends
* static_key_slow_inc/dec() down the slow path, and it is non-zero
- * so it counts as "enabled" in jump_label_update(). Note that
- * atomic_inc_unless_negative() checks >= 0, so roll our own.
+ * so it counts as "enabled" in jump_label_update().
+ *
+ * The INT_MAX overflow condition is either used by the networking
+ * code to reset or detected in the slow path of
+ * static_key_slow_inc_cpuslocked().
*/
v = atomic_read(&key->enabled);
do {
- if (v <= 0 || (v + 1) < 0)
+ if (v <= 0 || v == INT_MAX)
return false;
} while (!likely(atomic_try_cmpxchg(&key->enabled, &v, v + 1)));
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