Commit 695ef796 authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Peter Zijlstra
Browse files

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: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20240610124406.484973160@linutronix.de
parent 83ab38ef

kernel/jump_label.c

+6 −3
Original line number Diff line number Diff line
@@ -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)));