linux-kernel - [PATCH v2 1/3] locking/csd_lock: Print large numbers as negatives

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Message-Id: <20240722133735.667161-1-neeraj.upadhyay@kernel.org>
Date: Mon, 22 Jul 2024 19:07:33 +0530
From: neeraj.upadhyay@...nel.org
To: linux-kernel@...r.kernel.org
Cc: rcu@...r.kernel.org,
	kernel-team@...a.com,
	rostedt@...dmis.org,
	mingo@...nel.org,
	peterz@...radead.org,
	paulmck@...nel.org,
	leobras@...hat.com,
	imran.f.khan@...cle.com,
	riel@...riel.com,
	neeraj.upadhyay@...nel.org,
	tglx@...utronix.de
Subject: [PATCH v2 1/3] locking/csd_lock: Print large numbers as negatives

From: "Paul E. McKenney" <paulmck@...nel.org>

The CSD-lock-hold diagnostics from CONFIG_CSD_LOCK_WAIT_DEBUG are
printed in nanoseconds as unsigned long longs, which is a bit obtuse for
human readers when timing bugs result in negative CSD-lock hold times.
Yes, there are some people to whom it is immediately obvious that
18446744073709551615 is really -1, but for the rest of us...

Therefore, print these numbers as signed long longs, making the negative
hold times immediately apparent.

Reported-by: Rik van Riel <riel@...riel.com>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
Cc: Imran Khan <imran.f.khan@...cle.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Leonardo Bras <leobras@...hat.com>
Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>
Cc: Rik van Riel <riel@...riel.com>
Reviewed-by: Rik van Riel <riel@...riel.com>
Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@...nel.org>
---
 kernel/smp.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/smp.c b/kernel/smp.c
index f085ebcdf9e7..81f7083a53e2 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -248,8 +248,8 @@ static bool csd_lock_wait_toolong(call_single_data_t *csd, u64 ts0, u64 *ts1, in
 	cpu_cur_csd = smp_load_acquire(&per_cpu(cur_csd, cpux)); /* Before func and info. */
 	/* How long since this CSD lock was stuck. */
 	ts_delta = ts2 - ts0;
-	pr_alert("csd: %s non-responsive CSD lock (#%d) on CPU#%d, waiting %llu ns for CPU#%02d %pS(%ps).\n",
-		 firsttime ? "Detected" : "Continued", *bug_id, raw_smp_processor_id(), ts_delta,
+	pr_alert("csd: %s non-responsive CSD lock (#%d) on CPU#%d, waiting %lld ns for CPU#%02d %pS(%ps).\n",
+		 firsttime ? "Detected" : "Continued", *bug_id, raw_smp_processor_id(), (s64)ts_delta,
 		 cpu, csd->func, csd->info);
 	/*
 	 * If the CSD lock is still stuck after 5 minutes, it is unlikely
-- 
2.40.1