* Re: [PATCH] tty/serial/8250: make touch watchdog settable
[not found] ` <X/VnrvmN4k8UrXad@jagdpanzerIV.localdomain>
@ 2021-01-06 9:28 ` chenzhen (R)
2021-01-06 10:14 ` Sergey Senozhatsky
0 siblings, 1 reply; 2+ messages in thread
From: chenzhen (R) @ 2021-01-06 9:28 UTC (permalink / raw)
To: Sergey Senozhatsky
Cc: gregkh, jirislaby, andriy.shevchenko, lukas, Sergey.Semin,
vigneshr, rose.chen, linux-kernel
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
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [PATCH] tty/serial/8250: make touch watchdog settable
2021-01-06 9:28 ` [PATCH] tty/serial/8250: make touch watchdog settable chenzhen (R)
@ 2021-01-06 10:14 ` Sergey Senozhatsky
0 siblings, 0 replies; 2+ messages in thread
From: Sergey Senozhatsky @ 2021-01-06 10:14 UTC (permalink / raw)
To: chenzhen (R)
Cc: Sergey Senozhatsky, gregkh, jirislaby, andriy.shevchenko, lukas,
Sergey.Semin, vigneshr, rose.chen, linux-kernel
On (21/01/06 17:28), chenzhen (R) wrote:
> 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.
This is the intention. Suppose that serial8250 triggers the lockup
watchdog, how are you going to fix it? If you need to write NNNNN
bytes to the slow 8250 port then there is nothing you can do about
it; triggering watchdog from the 8250 write path is certainly not
going to help. If you have an excessive number of printk()-s then
reduce the number of spurious printk()-s (ratelimit, etc).
-ss
^ permalink raw reply [flat|nested] 2+ messages in thread
end of thread, other threads:[~2021-01-06 10:14 UTC | newest]
Thread overview: 2+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
[not found] <20210106064641.2621838-1-chenzhen105@huawei.com>
[not found] ` <X/VnrvmN4k8UrXad@jagdpanzerIV.localdomain>
2021-01-06 9:28 ` [PATCH] tty/serial/8250: make touch watchdog settable chenzhen (R)
2021-01-06 10:14 ` Sergey Senozhatsky
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).