linux-kernel - Re: [PATCH 1/1] thermal/sysfs: Clear the slot left in cooling_device_attr

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Date:   Wed, 22 Jun 2022 15:55:00 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Di Shen <di.shen@...soc.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        "Zhang, Rui" <rui.zhang@...el.com>, xuewen.yan@...soc.com,
        cindygm567@...il.com, Daniel Lezcano <daniel.lezcano@...aro.org>,
        Amit Kucheria <amitk@...nel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Lukasz Luba <lukasz.luba@....com>
Subject: Re: [PATCH 1/1] thermal/sysfs: Clear the slot left in cooling_device_attr_groups

On Mon, Jun 20, 2022 at 3:20 PM Di Shen <di.shen@...soc.com> wrote:
>
> There's a space allocated for cooling_device_stats_attr_group within co-

Please don't break words in the changelog (and variable names in
particular) like this.

> oling_device_attr_groups. This space is shared by all cooling devices.
>
> If not clear this space before cooling_device_stats_attr_group is initi-
> alized, the next cooling device will still create stats sysfs file node.
> At this time, read or write related nodes will cause kernel crash.

A bit more of an explanation here wouldn't hurt IMV.  In particular,
what does "the next cooling device" mean and what are "related nodes"?

> [exception_reboot_reason]: kernel_crash
> [exception_panic_reason]: Fatal exception
> [exception_time]: 2022-06-07_06-32-25
> [exception_file_info]: not-bugon
> [exception_task_id]: 3154
> [exception_task_family]: [cat, 3154][sh, 2597][sh, 2362][adbd, 1804]
> [exception_pc_symbol]: [<747516ae>] _raw_spin_lock+0x20/0x60
> [exception_stack_info]: [<4cbe9ac1>] prepare_exception_info+0x19c/0x1a4
> [<03041be7>] sysdump_panic_event+0x57c/0x6f4
> [<b16f865e>] atomic_notifier_call_chain+0x48/0x7c
> [<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
>
> So clear the slot left in cooling_device_attr_groups before cooling_dev-
> ice_stats_attr_group is initialized to avoid kernel crash.
>
> Signed-off-by: Di Shen <di.shen@...soc.com>
> ---
>  drivers/thermal/thermal_sysfs.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/drivers/thermal/thermal_sysfs.c b/drivers/thermal/thermal_sysfs.c
> index 1c4aac8464a7..fbc3dbc85841 100644
> --- a/drivers/thermal/thermal_sysfs.c
> +++ b/drivers/thermal/thermal_sysfs.c
> @@ -817,6 +817,11 @@ static void cooling_device_stats_setup(struct thermal_cooling_device *cdev)
>         unsigned long states;
>         int var;
>
> +       /* Clear the slot left in cooling_device_attr_groups */

The comment is a bit too vague IMO.  In particular, what slot do you mean?

> +       var = ARRAY_SIZE(cooling_device_attr_groups) - 2;
> +       if (cooling_device_attr_groups[var])
> +               cooling_device_attr_groups[var] = NULL;

The NULL check above is redundant (it can be cleared even if it is
NULL already) and it all can be done in one code line.

> +
>         if (cdev->ops->get_max_state(cdev, &states))
>                 return;
>
> --