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From: Guenter Roeck <linux@roeck-us.net>
To: Muni Sekhar <munisekharrms@gmail.com>,
	linux-watchdog@vger.kernel.org, linux-pci@vger.kernel.org,
	wim@linux-watchdog.org
Subject: Re: watchdog: how to enable?
Date: Fri, 15 Nov 2019 17:04:50 -0800
Message-ID: <0d5c20b1-6b0f-430b-17b0-d3624062020d@roeck-us.net> (raw)
In-Reply-To: <CAHhAz+h6SuGKWn0qNqsCdNjDks_vHuJW-KfiQja_b3x8x=vq_A@mail.gmail.com>

On 11/15/19 4:35 PM, Muni Sekhar wrote:
> [ Please keep me in CC as I'm not subscribed to the list]
> 
> Hi All,
> 
> My kernel is built with the following options:
> 
> $ cat /boot/config-5.0.1 | grep NO_HZ
> CONFIG_NO_HZ_COMMON=y
> CONFIG_NO_HZ_IDLE=y
> # CONFIG_NO_HZ_FULL is not set
> CONFIG_NO_HZ=y
> CONFIG_RCU_FAST_NO_HZ=y
> 
> I booted with watchdog enabled(nmi_watchdog=1) as given below:
> 
> BOOT_IMAGE=/boot/vmlinuz-5.0.1
> root=UUID=f65454ae-3f1d-4b9e-b4be-74a29becbe1e ro debug
> ignore_loglevel console=ttyUSB0,115200 console=tty0 console=tty1
> console=ttyS2,115200 memmap=1M!1023M nmi_watchdog=1
> crashkernel=384M-:128M
> 
> When the system is frozen or the kernel is locked up(I noticed that in
> this state kernel is not responding for ALT-SysRq-<command key>) but
> watchdog is not triggered. So I want to understand how to enable the
> watchdog timer and how to verify the basic watchdog functionality
> behavior?
>  > Any pointers on this will be greatly appreciated.
> 
Sorry, I do not have an answer. Please note that you are talking about
the NMI watchdog, which is completely unrelated to hardware watchdogs
and not handled by the watchdog subsystem. I would suggest to send
your question to the Linux kernel mailing list and clearly state
that you are talking about the NMI watchdog.

Please note that, for the NMI watchdog to do anything, you must have
CONFIG_HARDLOCKUP_DETECTOR enabled in your kernel configuration. I don't
know what if anything the configuration options you listed above have
to do with the NMI watchdog.

Another possibility, of course, might be to enable a hardware watchdog
in your system (assuming it supports one). I personally would not trust
the NMI watchdog because to detect a system hang, after all, there are
situations where even NMIs no longer work.

Guenter

  reply index

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-16  0:35 Muni Sekhar
2019-11-16  1:04 ` Guenter Roeck [this message]
2019-11-16  3:03   ` Muni Sekhar
2019-11-16 16:01     ` Guenter Roeck
2019-11-16 18:34       ` Muni Sekhar
2019-11-16 21:42         ` Guenter Roeck
2019-11-18  9:52           ` Muni Sekhar
2019-11-18 14:10             ` Guenter Roeck
2019-11-18 15:07               ` Muni Sekhar
2019-11-18 14:38 ` Bjorn Helgaas
2019-11-18 14:41   ` Bjorn Helgaas
2019-11-18 15:09   ` Muni Sekhar
2019-11-22 10:59     ` Guenter Roeck
2019-11-22 12:54       ` Muni Sekhar

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