linux-kernel - [PATCH AUTOSEL 5.8 51/62] locking/lockdep: Fix overflow in presentation of average lock-time

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Date:   Fri, 21 Aug 2020 12:14:12 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Chris Wilson <chris@...is-wilson.co.uk>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH AUTOSEL 5.8 51/62] locking/lockdep: Fix overflow in presentation of average lock-time

From: Chris Wilson <chris@...is-wilson.co.uk>

[ Upstream commit a7ef9b28aa8d72a1656fa6f0a01bbd1493886317 ]

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>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Link: https://lore.kernel.org/r/20200725185110.11588-1-chris@chris-wilson.co.uk
Signed-off-by: Sasha Levin <sashal@...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 5525cd3ba0c83..02ef87f50df29 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)
-- 
2.25.1