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

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Date:	Wed, 13 Jan 2016 08:27:33 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Kefeng Wang <wangkefeng.wang@...wei.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

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.

							Thanx, Paul

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