[PATCH 4.9 28/78] locking/lockdep: Fix overflow in presentation of average lock-time

Greg Kroah-Hartman
2020-09-01T15:16:36Z

From: Chris Wilson <chris@chris-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@chris-wilson.co.uk>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20200725185110.11588-1-chris@chris-wilson.co.uk
Signed-off-by: Sasha Levin <sashal@kernel.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 75d80809c48c9..09bad6cbb95cf 100644
--- a/kernel/locking/lockdep_proc.c
+++ b/kernel/locking/lockdep_proc.c
@@ -425,7 +425,7 @@ 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