linux-kernel - Re: [BUG] hwmon: (adt7470) warning when removing the module

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Date:   Thu, 7 Apr 2022 07:01:44 +0200
From:   Armin Wolf <W_Armin@....de>
To:     Zheyu Ma <zheyuma97@...il.com>, jdelvare@...e.com,
        linux@...ck-us.net
Cc:     linux-hwmon@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [BUG] hwmon: (adt7470) warning when removing the module

Am 07.04.22 um 05:17 schrieb Zheyu Ma:

> I found a bug when removing the adt7470 module.
>
> The following log can reveal it:
>
> [   18.459479] ------------[ cut here ]------------
> [   18.459852] do not call blocking ops when !TASK_RUNNING; state=1
> set at [<ffffffffa006052b>] adt7470_update_thread+0x7b/0x130 [adt7470]
> [   18.460857] WARNING: CPU: 7 PID: 365 at kernel/sched/core.c:9660
> __might_sleep+0x96/0xb0
> [   18.461523] Modules linked in: adt7470(-)
> [   18.464568] RIP: 0010:__might_sleep+0x96/0xb0
> [   18.472577] Call Trace:
> [   18.472778]  <TASK>
> [   18.472957]  exit_signals+0x2f/0x3b0
> [   18.473251]  do_exit+0xcd/0x18c0
> [   18.473534]  ? __mutex_unlock_slowpath+0x1b8/0x740
> [   18.473927]  kthread_exit+0x42/0x60
> [   18.474212]  ? adt7470_detect+0x140/0x140 [adt7470]
> [   18.474622]  kthread+0x272/0x2e0
> [   18.474885]  ? adt7470_detect+0x140/0x140 [adt7470]
> [   18.475277]  ? kthread_blkcg+0xa0/0xa0
> [   18.475601]  ret_from_fork+0x22/0x30
> [   18.475901]  </TASK>
>
> Regards,
> Zheyu Ma

Please correct me if i am wrong, but i think the issue lies in adt7470_update_thread()
leaving the kthread in TASK_INTERRUPTIBLE state when the second check for kthread_should_stop()
returns true and causes the kthread to exit. Since kthread_exit() might sleep in exit_signals(),
we get this warning.
Maybe moving set_current_state(TASK_INTERRUPTIBLE) below the second check for kthread_should_stop()
would fix the issue?

Armin Wolf