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SubjectRe: [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@joshtriplett.org>
> > Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.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 ",
> >
>

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