linux-kernel - Re: [PATCH 0/5] improve handling of errors returned by kthread

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Date:	Mon, 12 Oct 2015 17:13:54 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	Ulrich Obergfell <uobergfe@...hat.com>
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	atomlin@...hat.com
Subject: Re: [PATCH 0/5] improve handling of errors returned by kthread_park()

On Mon, Sep 28, 2015 at 10:44:07PM +0200, Ulrich Obergfell wrote:
> The original watchdog_park_threads() function that was introduced by
> commit 81a4beef91ba4a9e8ad6054ca9933dff7e25ff28 takes a very simple
> approach to handle errors returned by kthread_park(): It attempts to
> roll back all watchdog threads to the unparked state. However, this
> may be undesired behaviour from the perspective of the caller which
> may want to handle errors as appropriate in its specific context.
> Currently, there are two possible call chains:


I spent a little time cleaning up some of my test scripts for this code.
Things seem to work well.  Hardlockups and softlockups work along with
enabling/disabling the various lockup knobs.

Acked-by: Don Zickus <dzickus@...hat.com>

> 
> - watchdog suspend/resume interface
> 
>     lockup_detector_suspend
>       watchdog_park_threads
> 
> - write to parameters in /proc/sys/kernel
> 
>     proc_watchdog_update
>       watchdog_enable_all_cpus
>         update_watchdog_all_cpus
>           watchdog_park_threads
> 
> Instead of 'blindly' attempting to unpark the watchdog threads if a 
> kthread_park() call fails, the new approach is to disable the lockup
> detectors in the above call chains. Failure becomes visible to the
> user as follows:
> 
> - error messages from lockup_detector_suspend()
>                    or watchdog_enable_all_cpus()
> 
> - the state that can be read from /proc/sys/kernel/watchdog_enabled
> 
> - the 'write' system call in the latter call chain returns an error
> 
> Ulrich Obergfell (5):
>   watchdog: fix error handling in proc_watchdog_thresh()
>   watchdog: move watchdog_disable_all_cpus() outside of ifdef
>   watchdog: implement error handling in update_watchdog_all_cpus() and
>     callers
>   watchdog: implement error handling in lockup_detector_suspend()
>   watchdog: do not unpark threads in watchdog_park_threads() on error
> 
>  kernel/watchdog.c | 60 +++++++++++++++++++++++++++++++++++++++----------------
>  1 file changed, 43 insertions(+), 17 deletions(-)
> 
> -- 
> 1.7.11.7
> 
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