The following commit has been merged into the locking/core branch of tip:
Commit-ID: 695ef796467ed228b60f1915995e390aea3d85c6
Gitweb: https://git.kernel.org/tip/695ef796467ed228b60f1915995e390aea3d85c6
Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate: Mon, 10 Jun 2024 14:46:37 +02:00
Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Tue, 11 Jun 2024 11:25:23 +02:00
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@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20240610124406.484973160@xxxxxxxxxxxxx
---
kernel/jump_label.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index 1f05a19..4d06ec2 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -132,12 +132,15 @@ bool static_key_fast_inc_not_disabled(struct static_key *key)
/*
* 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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