linux-kernel - Re: [PATCH v2 1/8] x86: speed up int3-based patching using less paranoid write

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Date:	Fri, 8 Nov 2013 09:49:51 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	Petr Mladek <pmladek@...e.cz>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Jiri Kosina <jkosina@...e.cz>, linux-kernel@...r.kernel.org,
	x86@...nel.org
Subject: Re: [PATCH v2 1/8] x86: speed up int3-based patching using less
 paranoid write

On Fri, 08 Nov 2013 21:04:26 +0900
Masami Hiramatsu <masami.hiramatsu.pt@...achi.com> wrote:


> >  static void do_sync_core(void *info)
> >  {
> >  	sync_core();
> > @@ -648,15 +687,15 @@ void *text_poke_bp(void *addr, const void *opcode, size_t len, void *handler)
> >  	 */
> >  	smp_wmb();
> >  
> > -	text_poke(addr, &int3, sizeof(int3));
> > +	text_poke_part(addr, &int3, sizeof(int3));
> 
> Anyway, text_poke itself will cause a BUG if it hits an error, but text_poke_part() seems
> silently failing. It should handle the error correctly (or call BUG()).
> 

text_poke_part() shouldn't do a bug on error, but this code probably
should.

	if (text_poke_part(addr, &int3, sizeof(int3)))
		BUG();

Note, I would avoid doing:

	BUG_ON(text_poke_part(...));

as we don't want "side effects" in the BUG() macros. You may do:

	ret = text_poke_part(...);
	BUG_ON(ret);

Which has the added benefit of the implicit "unlikely" in the BUG_ON()
macro.

Or we can have do_sync_core() be able to handle errors and have their
callers handle them too.

-- Steve
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