linux-kernel - Re: [PATCH] tty/serial/8250: make touch watchdog settable

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Message-ID: <db5f51df-3a3e-41a6-00e3-234575c07ec6@huawei.com>
Date:   Wed, 6 Jan 2021 17:28:57 +0800
From:   "chenzhen (R)" <chenzhen105@...wei.com>
To:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>
CC:     <gregkh@...uxfoundation.org>, <jirislaby@...nel.org>,
        <andriy.shevchenko@...ux.intel.com>, <lukas@...ner.de>,
        <Sergey.Semin@...kalelectronics.ru>, <vigneshr@...com>,
        <rose.chen@...wei.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tty/serial/8250: make touch watchdog settable


On 21/1/6 15:33, Sergey Senozhatsky wrote:
> On (21/01/06 14:46), chenzhen wrote:
>> Since 54f19b4a6(tty/serial/8250: Touch NMI watchdog in wait_for_xmitr), serial8250
>> will always touch watchdog in write and wait_for_xmitr. However, serial8250 may
>> become low speed thus take a long time to print. In this process, nmi and soft
>> watchdog on current CPU will be invalid.
>>
>> To resolve this problem, add a cmdline option "tty_watchdog_enable" to control
>> the touchdog in serial8250.
> Sorry, I don't understand - what does this fix?
>
> 	-ss
> .

It fixes that if serial8250 is low speed on some machine, when it writes for a long time, NMI/softlockup watchdog will never bark and potential rlock will not be detected. So an option to control the touchdog in serial8250 may help.

Thanks for your reply!

                                                                 -Zhen Chen