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

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Date:   Tue, 7 Nov 2017 14:01:58 -0600
From:   Jeremy Linton <jeremy.linton@....com>
To:     linux-kernel@...r.kernel.org
Cc:     peterz@...radead.org, mingo@...hat.com
Subject: Re: [PATCH] locktorture: Fix Oops when reader/writer count is 0

Hi,

On 10/10/2017 10:52 AM, Jeremy Linton wrote:
> If nwriters_stress=0 is passed to the lock torture test
> it will panic in:

Ping?

Has anyone had a chance to look at this?

Thanks,

> 
> 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;
>