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

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Date:	Thu, 14 Jan 2016 09:38:04 +0800
From:	Kefeng Wang <wangkefeng.wang@...wei.com>
To:	<paulmck@...ux.vnet.ibm.com>
CC:	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	<linux-kernel@...r.kernel.org>, <guohanjun@...wei.com>
Subject: Re: [PATCH] locktorture: Fix NULL pointer when torture_type is
 invalid

Hi paul,

On 2016/1/14 0:27, Paul E. McKenney wrote:
> On Wed, Jan 13, 2016 at 10:06:22AM +0800, 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=0000000000000000
>> 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 stats_task in lock_torture_cleanup() to guard not into
>> a wrong path.
>>
>> Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.com>
> 
> Good catch!  One question below...
> 
>> ---
>>  kernel/locking/locktorture.c | 6 ++++--
>>  1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/locking/locktorture.c b/kernel/locking/locktorture.c
>> index 8ef1919..1afa8ad 100644
>> --- a/kernel/locking/locktorture.c
>> +++ b/kernel/locking/locktorture.c
>> @@ -764,8 +764,10 @@ static void lock_torture_cleanup(void)
>>  		reader_tasks = NULL;
>>  	}
>>
>> -	torture_stop_kthread(lock_torture_stats, stats_task);
>> -	lock_torture_stats_print();  /* -After- the stats thread is stopped! */
>> +	if (stats_task) {
>> +		torture_stop_kthread(lock_torture_stats, stats_task);
>> +		lock_torture_stats_print();  /* -After- the stats thread is stopped! */
>> +	}
> 
> Does it work to have the following?
> 
> +	if (stats_task)
> +		torture_stop_kthread(lock_torture_stats, stats_task);
> +	lock_torture_stats_print();  /* -After- the stats thread is stopped! */
> 
> We need to print the statistics at the end of the run, even if we chose
> not to print them periodically throughout the run.
> 

No, the pc is in __torture_print_stats(char *page, struct lock_stress_stats *statp, bool write),
that is 'long min = statp[0].n_lock_acquired;', if the torture_type is invalid, the statp is NULL,
because the cxt.lwsa and cxt.lwsa/cxt.lrsa are not initialized in lock_torture_init().

Thanks,
Kefeng

> 							Thanx, Paul
> 
>>  	if (atomic_read(&cxt.n_lock_torture_errors))
>>  		lock_torture_print_module_parms(cxt.cur_ops,
>> -- 
>> 1.7.12.4
>>
> 
> 
> .
>