linux-kernel - [PATCH] locktorture: Fix Oops when reader/writer count is 0

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Date:   Tue, 10 Oct 2017 10:52:48 -0500
From:   Jeremy Linton <jeremy.linton@....com>
To:     linux-kernel@...r.kernel.org
Cc:     peterz@...radead.org, mingo@...hat.com,
        Jeremy Linton <jeremy.linton@....com>
Subject: [PATCH] locktorture: Fix Oops when reader/writer count is 0

If nwriters_stress=0 is passed to the lock torture test
it will panic in:

Internal error: Oops: 96000005 [#1] SMP
...
[<ffff000000b7022c>] __torture_print_stats+0x2c/0x1c8 [locktorture]
[<ffff000000b7070c>] lock_torture_stats_print+0x74/0x120 [locktorture]
[<ffff000000b707f8>] lock_torture_stats+0x40/0xa8 [locktorture]
[<ffff0000080f3570>] kthread+0x108/0x138
[<ffff000008084b90>] ret_from_fork+0x10/0x18

This is caused by the deference to a null statp. Fix that by
checking the n_stress for non zero count before referencing statp.

Signed-off-by: Jeremy Linton <jeremy.linton@....com>
---
 kernel/locking/locktorture.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/locking/locktorture.c b/kernel/locking/locktorture.c
index f24582d4dad3..8229ba7147e5 100644
--- a/kernel/locking/locktorture.c
+++ b/kernel/locking/locktorture.c
@@ -716,10 +716,14 @@ static void __torture_print_stats(char *page,
 	bool fail = 0;
 	int i, n_stress;
 	long max = 0;
-	long min = statp[0].n_lock_acquired;
+	long min = 0;
 	long long sum = 0;
 
 	n_stress = write ? cxt.nrealwriters_stress : cxt.nrealreaders_stress;
+
+	if (n_stress)
+		min = statp[0].n_lock_acquired;
+
 	for (i = 0; i < n_stress; i++) {
 		if (statp[i].n_lock_fail)
 			fail = true;
-- 
2.13.5