linux-kernel - Re: [PATCH v2] locktorture: Fix NULL pointer when torture

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Date:	Sat, 30 Jan 2016 10:46:57 +0800
From:	Kefeng Wang <wangkefeng.wang@...wei.com>
To:	"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
	<linux-kernel@...r.kernel.org>
CC:	<peterz@...radead.org>, <mingo@...hat.com>,
	Josh Triplett <josh@...htriplett.org>,
	"Guohanjun (Hanjun Guo)" <guohanjun@...wei.com>
Subject: Re: [PATCH v2] locktorture: Fix NULL pointer when torture_type is
 invalid

Hi Paul,

On 2016/1/28 12:25, Kefeng Wang wrote:
> Insmod locktorture with torture_type=mutex will lead to crash,
> 
> Unable to handle kernel NULL pointer dereference at virtual address 00000008
> pgd = ffffffc0f6c10000
> [00000008] *pgd=000000013b221003, *pud=000000013b221003, *pmd=0000000000000000a
> Internal error: Oops: 94000006 [#1] PREEMPT SMP
> Modules linked in: locktorture(+) torture
> CPU: 2 PID: 1462 Comm: insmod Not tainted 4.4.0+ #19
> Hardware name: linux,dummy-virt (DT)
> task: ffffffc0fb2b3700 ti: ffffffc0fa938000 task.ti: ffffffc0fa938000
> PC is at __torture_print_stats+0x18/0x180 [locktorture]
> LR is at lock_torture_stats_print+0x68/0x110 [locktorture]
> pc : [<ffffffbffc017028>] lr : [<ffffffbffc017500>] pstate: 60000145
> sp : ffffffc0fa93bb20
> [snip...]
> Call trace:
> [<ffffffbffc017028>] __torture_print_stats+0x18/0x180 [locktorture]
> [<ffffffbffc017500>] lock_torture_stats_print+0x68/0x110 [locktorture]
> [<ffffffbffc0180fc>] lock_torture_cleanup+0xc4/0x278 [locktorture]
> [<ffffffbffc01d144>] lock_torture_init+0x144/0x5b0 [locktorture]
> [<ffffffc000082940>] do_one_initcall+0x94/0x1a0
> [<ffffffc000141888>] do_init_module+0x60/0x1c8
> [<ffffffc00011c628>] load_module+0x1880/0x1c9c
> [<ffffffc00011cc00>] SyS_finit_module+0x7c/0x88
> [<ffffffc000085cb0>] el0_svc_naked+0x24/0x28
> 
> Fix it by check statp in __torture_print_stats(), if it is NULL, just
> create a lock-torture-statistics message with zero statistic argument.

It is keep to get the statistics printout at the end if with bad argument,
what's your opinion about this version？

Thanks,
Kefeng

> 
> Cc: Josh Triplett <josh@...htriplett.org>
> Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.com>
> ---
>  kernel/locking/locktorture.c | 24 ++++++++++++++----------
>  1 file changed, 14 insertions(+), 10 deletions(-)
> 
> diff --git a/kernel/locking/locktorture.c b/kernel/locking/locktorture.c
> index 8ef1919..7f0cf9c 100644
> --- a/kernel/locking/locktorture.c
> +++ b/kernel/locking/locktorture.c
> @@ -647,19 +647,23 @@ 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;
> -	for (i = 0; i < n_stress; i++) {
> -		if (statp[i].n_lock_fail)
> -			fail = true;
> -		sum += statp[i].n_lock_acquired;
> -		if (max < statp[i].n_lock_fail)
> -			max = statp[i].n_lock_fail;
> -		if (min > statp[i].n_lock_fail)
> -			min = statp[i].n_lock_fail;
> +	if (statp) {
> +		min = statp[0].n_lock_acquired;
> +		n_stress = write ? cxt.nrealwriters_stress : cxt.nrealreaders_stress;
> +		for (i = 0; i < n_stress; i++) {
> +			if (statp[i].n_lock_fail)
> +				fail = true;
> +			sum += statp[i].n_lock_acquired;
> +			if (max < statp[i].n_lock_fail)
> +				max = statp[i].n_lock_fail;
> +			if (min > statp[i].n_lock_fail)
> +				min = statp[i].n_lock_fail;
> +		}
>  	}
> +
>  	page += sprintf(page,
>  			"%s:  Total: %lld  Max/Min: %ld/%ld %s  Fail: %d %s\n",
>  			write ? "Writes" : "Reads ",
>