linux-kernel - Re: [RFC][PATCH 5/7] jump_label: Rework update logic

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Message-ID: <20150727090737.GO19282@twins.programming.kicks-ass.net>
Date:	Mon, 27 Jul 2015 11:07:37 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	linux-kernel@...r.kernel.org, mingo@...nel.org
Cc:	jasonbaron0@...il.com, bp@...en8.de, luto@...capital.net,
	tglx@...utronix.de, rostedt@...dmis.org, will.deacon@....com,
	liuj97@...il.com, rabin@....in, ralf@...ux-mips.org,
	ddaney@...iumnetworks.com, benh@...nel.crashing.org,
	michael@...erman.id.au, heiko.carstens@...ibm.com,
	davem@...emloft.net
Subject: Re: [RFC][PATCH 5/7] jump_label: Rework update logic

On Fri, Jul 24, 2015 at 07:52:14PM +0200, Peter Zijlstra wrote:
> @@ -330,8 +318,7 @@ static int jump_label_add_module(struct
>  		jlm->next = key->next;
>  		key->next = jlm;
>  
> -		if (jump_label_type(key) == JUMP_LABEL_JMP)
> -			__jump_label_update(key, iter, iter_stop, JUMP_LABEL_JMP);
> +		__jump_label_update(key, iter, iter_stop);
>  	}
>  
>  	return 0;

That is the fail; the arch_jump_label_transform() function (at least on
x86) double checks that we're changing the branch, so we cannot
unconditionally write whatever it should be.


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