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

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Date:	Sat, 30 Jan 2016 16:27:21 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Kefeng Wang <wangkefeng.wang@...wei.com>
Cc:	linux-kernel@...r.kernel.org, peterz@...radead.org,
	mingo@...hat.com, Josh Triplett <josh@...htriplett.org>,
	"Guohanjun (Hanjun Guo)" <guohanjun@...wei.com>, dave@...olabs.net
Subject: Re: [PATCH v2] locktorture: Fix NULL pointer when torture_type is
 invalid

On Sat, Jan 30, 2016 at 10:46:57AM +0800, Kefeng Wang wrote:
> 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？

Hello, Kefeng,

Well, it does look like it would prevent the NULL pointer dereference,
but I was hoping for something that would print the full statistics
at the end regardless of the periodic statistics.

But I am adding Davidlohr on CC, as he seems to be the major user
of locktorture.

							Thanx, Paul

> 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 ",
> > 
>