linux-kernel - [PATCH v4 17/30] sched/clock, x86: Mark __sched_clock

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Message-ID: <20250114175143.81438-18-vschneid@redhat.com>
Date: Tue, 14 Jan 2025 18:51:30 +0100
From: Valentin Schneider <vschneid@...hat.com>
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Subject: [PATCH v4 17/30] sched/clock, x86: Mark __sched_clock_stable key as allowed in .noinstr

Later commits will cause objtool to warn about static keys being used in
.noinstr sections in order to safely defer instruction patching IPIs
targeted at NOHZ_FULL CPUs.

__sched_clock_stable is used in .noinstr code, and can be modified at
runtime (e.g. time_cpufreq_notifier()). Suppressing the text_poke_sync()
IPI has little benefits for this key, as NOHZ_FULL is incompatible with an
unstable TSC anyway.

Mark it to let objtool know not to warn about it.

Signed-off-by: Valentin Schneider <vschneid@...hat.com>
---
 kernel/sched/clock.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c
index 200e5568b9894..e59986bc14a43 100644
--- a/kernel/sched/clock.c
+++ b/kernel/sched/clock.c
@@ -75,8 +75,11 @@ static DEFINE_STATIC_KEY_FALSE_RO(sched_clock_running);
  *
  * Similarly we start with __sched_clock_stable_early, thereby assuming we
  * will become stable, such that there's only a single 1 -> 0 transition.
+ *
+ * Allowed in .noinstr as an unstable TLC is incompatible with NOHZ_FULL,
+ * thus the text patching IPI would be the least of our concerns.
  */
-static DEFINE_STATIC_KEY_FALSE(__sched_clock_stable);
+static DEFINE_STATIC_KEY_FALSE_NOINSTR(__sched_clock_stable);
 static int __sched_clock_stable_early = 1;
 
 /*
-- 
2.43.0