Re: [PATCH V2 1/1] thermal/sysfs: Clear cooling_device_stats_attr_group before initialized

[Di Shen]

On Sat, Jul 23, 2022 at 1:18 AM Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote:
>
> On Fri, Jul 22, 2022 at 10:44 AM Di Shen <di.shen@xxxxxxxxxx> wrote:
> >
> > There's a space allocated for cooling_device_stats_attr_group
> > within cooling_device_attr_groups. This space is shared by all
> > cooling devices.
>
> That's correct.
>
> > If the stats structure of one cooling device successfully
> > creates stats sysfs. After that, another cooling device fails
> > to get max_states in cooling_device_stats_setup(). It can
> > return directly without initializing the stats structure, but
> > the cooling_device_stats_attr_group is still the attribute
> > group of the last cooling device.
>
> I cannot parse the above, sorry.
>
> For example, how can a "stats structure of one cooling device" create
> anything?   As a data structure, it is a passive entity, so it doesn't
> carry out any actions.
>

Sorry, I didn't describe it properly. I mean 'if it has been called back
cooling_device_stats_setup() successfully for a cooling device'.

> I think (but I am not sure) that you are referring to the error code
> path in which the ->get_max_state() callback fails for a cooling
> device after cooling_device_stats_setup() has completed successfully
> for another one.
>

That's it. As you say, ->get_max_state() callback fails for a cooling
device after cooling_device_stats_setup() has completed successfully
for another one.

> > At this time, read or write stats sysfs nodes can cause kernel
> > crash. Like the following, kernel crashed when
> > 'cat time_in_state_ms'.
> >
> > [<5baac8d4>] panic+0x1b4/0x3c8
> > [<9d287b0f>] arm_notify_die+0x0/0x78
> > [<094fc22c>] __do_kernel_fault+0x94/0xa4
> > [<3b4b69a4>] do_page_fault+0xd4/0x364
> > [<23793e7a>] do_translation_fault+0x38/0xc0
> > [<6e5cc52a>] do_DataAbort+0x4c/0xd0
> > [<a28c16b8>] __dabt_svc+0x5c/0xa0
> > [<747516ae>] _raw_spin_lock+0x20/0x60
> > [<9a9e4cd4>] time_in_state_ms_show+0x28/0x148
> > [<cb78325e>] dev_attr_show+0x38/0x64
> > [<aea3e364>] sysfs_kf_seq_show+0x8c/0xf0
> > [<c0a843ab>] seq_read+0x244/0x620
> > [<b316b374>] vfs_read+0xd8/0x218
> > [<3aebf5fa>] sys_read+0x80/0xe4
> > [<7cf100f5>] ret_fast_syscall+0x0/0x28
> > [<08cbe22f>] 0xbe8c1198
> >
> > stats sysfs:
> > phone:/sys/class/thermal/cooling_device2/stats # ls
> > reset  time_in_state_ms  total_trans  trans_table
> >
> > The same as cat total_trans, trans_table, and echo reset.
> >
> > To avoid kernel crash, this patch set clears the
> > cooling_device_attr_groups before stats structure is initialized.
> >
> > Signed-off-by: Di Shen <di.shen@xxxxxxxxxx>
> > ---
> >  drivers/thermal/thermal_sysfs.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/drivers/thermal/thermal_sysfs.c b/drivers/thermal/thermal_sysfs.c
> > index 1c4aac8464a7..e3fae63fa0f7 100644
> > --- a/drivers/thermal/thermal_sysfs.c
> > +++ b/drivers/thermal/thermal_sysfs.c
> > @@ -817,6 +817,9 @@ static void cooling_device_stats_setup(struct thermal_cooling_device *cdev)
> >         unsigned long states;
> >         int var;
> >
> > +       var = ARRAY_SIZE(cooling_device_attr_groups) - 2;
> > +       cooling_device_attr_groups[var] = NULL;
> > +
> >         if (cdev->ops->get_max_state(cdev, &states))
> >                 return;
> >
> > --

--
Best regards,
Di



Di