linux-kernel - Re: klp_task_patch: was: [RFC PATCH v2 17/18] livepatch: change to a per-task consistency model

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Message-ID: <alpine.LNX.2.00.1605041651500.27942@cbobk.fhfr.pm>
Date:	Wed, 4 May 2016 16:56:34 +0200 (CEST)
From:	Jiri Kosina <jikos@...nel.org>
To:	Petr Mladek <pmladek@...e.com>
cc:	Josh Poimboeuf <jpoimboe@...hat.com>, Jessica Yu <jeyu@...hat.com>,
	Miroslav Benes <mbenes@...e.cz>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
	x86@...nel.org, linuxppc-dev@...ts.ozlabs.org,
	linux-s390@...r.kernel.org, Vojtech Pavlik <vojtech@...e.com>,
	Jiri Slaby <jslaby@...e.cz>,
	Chris J Arges <chris.j.arges@...onical.com>,
	Andy Lutomirski <luto@...nel.org>
Subject: Re: klp_task_patch: was: [RFC PATCH v2 17/18] livepatch: change to
 a per-task consistency model

On Wed, 4 May 2016, Petr Mladek wrote:

> > +
> > +		if (unlikely(klp_patch_pending(current)))
> > +			klp_patch_task(current);
> >  	}
> 
> Some more ideas from the world of crazy races. I was shaking my head
> if this was safe or not.
> 
> The problem might be if the task get rescheduled between the check
> for the pending stuff 

The code in question is running with preemption disabled.

> or inside the klp_patch_task() function. 

We must make sure that this function doesn't go to sleep. It's only used 
to clear the task_struct flag anyway.

-- 
Jiri Kosina
SUSE Labs