linux-kernel - [PATCH] locking/lockdep: Fix overflow in presentation of average lock-time

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Message-Id: <20200725185110.11588-1-chris@chris-wilson.co.uk>
Date:   Sat, 25 Jul 2020 19:51:10 +0100
From:   Chris Wilson <chris@...is-wilson.co.uk>
To:     linux-kernel@...r.kernel.org
Cc:     Chris Wilson <chris@...is-wilson.co.uk>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>
Subject: [PATCH] locking/lockdep: Fix overflow in presentation of average lock-time

Though the number of lock-acquisitions is tracked as unsigned long, this
is passed as the divisor to div_s64() which interprets it as a s32,
giving nonsense values with more than 2 billion acquisitons. E.g.

  acquisitions   holdtime-min   holdtime-max holdtime-total   holdtime-avg
  -------------------------------------------------------------------------
    2350439395           0.07         353.38   649647067.36          0.-32

Signed-off-by: Chris Wilson <chris@...is-wilson.co.uk>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Will Deacon <will@...nel.org>
---
 kernel/locking/lockdep_proc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/locking/lockdep_proc.c b/kernel/locking/lockdep_proc.c
index 5525cd3ba0c8..02ef87f50df2 100644
--- a/kernel/locking/lockdep_proc.c
+++ b/kernel/locking/lockdep_proc.c
@@ -423,7 +423,7 @@ static void seq_lock_time(struct seq_file *m, struct lock_time *lt)
 	seq_time(m, lt->min);
 	seq_time(m, lt->max);
 	seq_time(m, lt->total);
-	seq_time(m, lt->nr ? div_s64(lt->total, lt->nr) : 0);
+	seq_time(m, lt->nr ? div64_u64(lt->total, lt->nr) : 0);
 }
 
 static void seq_stats(struct seq_file *m, struct lock_stat_data *data)
-- 
2.20.1