linux-kernel - Re: [PATCH v6 2/2] misc: Add a mechanism to detect stalls on guest vCPUs

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Date:   Thu, 16 Jun 2022 06:08:51 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sebastian Ene <sebastianene@...gle.com>
Cc:     Rob Herring <robh+dt@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Dragan Cvetic <dragan.cvetic@...inx.com>,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        maz@...nel.org, will@...nel.org, vdonnefort@...gle.com,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH v6 2/2] misc: Add a mechanism to detect stalls on guest
 vCPUs

On 6/16/22 03:08, Greg Kroah-Hartman wrote:
> On Thu, Jun 16, 2022 at 09:27:39AM +0000, Sebastian Ene wrote:
>> This driver creates per-cpu hrtimers which are required to do the
>> periodic 'pet' operation. On a conventional watchdog-core driver, the
>> userspace is responsible for delivering the 'pet' events by writing to
>> the particular /dev/watchdogN node. In this case we require a strong
>> thread affinity to be able to account for lost time on a per vCPU.
>>
>> This part of the driver is the 'frontend' which is reponsible for
>> delivering the periodic 'pet' events, configuring the virtual peripheral
>> and listening for cpu hotplug events. The other part of the driver
>> handles the peripheral emulation and this part accounts for lost time by
>> looking at the /proc/{}/task/{}/stat entries and is located here:
>> https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/3548817
>>
>> Reported-by: kernel test robot <lkp@...el.com>
> 
> The robot reported stalls on vcpus?
> 

I have seen this a number of times when people fix issues reported by
the robot in their submissions, just because the robot asks them to
do so. This should really be part of the change log, such as

v17: Fixed the following issues issues reported by the kernel test robot:
      ...

Guenter