linux-kernel - Re: [PATCH v3 1/2] livepatch: send a fake signal to all blocking tasks

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Date:   Mon, 6 Nov 2017 12:08:33 +0100
From:   Pavel Machek <pavel@....cz>
To:     Miroslav Benes <mbenes@...e.cz>
Cc:     jpoimboe@...hat.com, jeyu@...nel.org, jikos@...nel.org,
        pmladek@...e.com, lpechacek@...e.cz, live-patching@...r.kernel.org,
        linux-kernel@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        linuxppc-dev@...ts.ozlabs.org, x86@...nel.org
Subject: Re: [PATCH v3 1/2] livepatch: send a fake signal to all blocking
 tasks

Hi!

> --- a/Documentation/ABI/testing/sysfs-kernel-livepatch
> +++ b/Documentation/ABI/testing/sysfs-kernel-livepatch
> @@ -33,6 +33,15 @@ Contact:	live-patching@...r.kernel.org
>  		An attribute which indicates whether the patch is currently in
>  		transition.
>  
> +What:		/sys/kernel/livepatch/<patch>/signal
> +Date:		Oct 2017
> +KernelVersion:	4.15.0
> +Contact:	live-patching@...r.kernel.org
> +Description:
> +		A writable attribute that allows administrator to affect the
> +		course of an existing transition. Writing 1 sends a signal to
> +		all remaining blocking tasks.

What kind of signal?

>  What:		/sys/kernel/livepatch/<patch>/<object>
>  Date:		Nov 2014
>  KernelVersion:	3.19.0
> diff --git a/Documentation/livepatch/livepatch.txt b/Documentation/livepatch/livepatch.txt
> index ecdb18104ab0..6694530d0894 100644
> --- a/Documentation/livepatch/livepatch.txt
> +++ b/Documentation/livepatch/livepatch.txt
> @@ -178,6 +178,12 @@ transition, it shows -1.  Any tasks which are blocking the transition
>  can be signaled with SIGSTOP and SIGCONT to force them to change their
>  patched state.
>  
> +Administrator can also affect a transition through
> +/sys/kernel/livepatch/<patch>/signal attribute. Writing 1 to the attribute sends
> +a signal to all remaining blocking tasks. This is an alternative for
> +SIGSTOP/SIGCONT approach mentioned in the previous paragraph. It should also be
> +less harmful to the system.

Well... If SIGSTOP / SIGCONT is considered harmful (it probably is),
it should be mentioned above, and not in note here...
									Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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