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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20150929163036.a1260608ab9b13273eebf9cb@linux-foundation.org>
Date:	Tue, 29 Sep 2015 16:30:36 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Ulrich Obergfell <uobergfe@...hat.com>
Cc:	linux-kernel@...r.kernel.org, dzickus@...hat.com,
	atomlin@...hat.com
Subject: Re: [PATCH 0/5] improve handling of errors returned by
 kthread_park()

On Mon, 28 Sep 2015 22:44:07 +0200 Ulrich Obergfell <uobergfe@...hat.com> 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:
> 
> - 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
> 

hm, you made me look at kthread parking.  Why does it exist?  What is a
"parked" thread anyway, and how does it differ from, say, a sleeping
one?  The 2a1d446019f9a5983ec5a335b changelog is pretty useless and the
patch added no useful documentation, sigh.

Anwyay...  what inspired this patchset?  Are you experiencing
kthread_park() failures in practice?  If so, what is causing them?  And
what is the user-visible effect of these failures?  This is all pretty
important context for such a patchset.


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/