linux-kernel - [patch v2] sched/debug: Change need_resched warnings to pr

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Message-ID: <e8d52023-5291-26bd-5299-8bb9eb604929@google.com>
Date: Thu, 9 Jan 2025 16:24:33 -0800 (PST)
From: David Rientjes <rientjes@...gle.com>
To: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, 
    Juri Lelli <juri.lelli@...hat.com>, 
    Vincent Guittot <vincent.guittot@...aro.org>
cc: Dietmar Eggemann <dietmar.eggemann@....com>, 
    Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>, 
    Mel Gorman <mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>, 
    linux-kernel@...r.kernel.org, 
    Madadi Vineeth Reddy <vineethr@...ux.ibm.com>, 
    Josh Don <joshdon@...gle.com>
Subject: [patch v2] sched/debug: Change need_resched warnings to pr_err

need_resched warnings, if enabled, are treated as WARNINGs.  If
kernel.panic_on_warn is enabled, then this causes a kernel panic.

It's highly unlikely that a panic is desired for these warnings, only a
stack trace is normally required to debug and resolve.

Thus, switch need_resched warnings to simply be a printk with an
associated stack trace so they are no longer in scope for panic_on_warn.

Acked-by: Josh Don <joshdon@...gle.com>
Reviewed-by: Madadi Vineeth Reddy <vineethr@...ux.ibm.com>
Signed-off-by: David Rientjes <rientjes@...gle.com>
---
 v2: added Acked-by and Reviewed-by, dropped second patch in the series

 kernel/sched/debug.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -1295,8 +1295,10 @@ void resched_latency_warn(int cpu, u64 latency)
 {
 	static DEFINE_RATELIMIT_STATE(latency_check_ratelimit, 60 * 60 * HZ, 1);
 
-	WARN(__ratelimit(&latency_check_ratelimit),
-	     "sched: CPU %d need_resched set for > %llu ns (%d ticks) "
-	     "without schedule\n",
-	     cpu, latency, cpu_rq(cpu)->ticks_without_resched);
+	if (likely(!__ratelimit(&latency_check_ratelimit)))
+		return;
+
+	pr_err("sched: CPU %d need_resched set for > %llu ns (%d ticks) without schedule\n",
+	       cpu, latency, cpu_rq(cpu)->ticks_without_resched);
+	dump_stack();
 }