linux-kernel - Re: Regression :-) Re: [GIT PULL RESEND] x86/jumpmplabel changes for v3.12-rc1

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Date:	Wed, 11 Sep 2013 10:56:33 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Jason Baron <jbaron@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	boris.ostrovsky@...cle.com, david.vrabel@...rix.com
Subject: Re: Regression :-) Re: [GIT PULL RESEND] x86/jumpmplabel changes
 for v3.12-rc1

On Wed, 11 Sep 2013 10:25:45 -0400
Konrad Rzeszutek Wilk <konrad.wilk@...cle.com> wrote:

> > It seems to imply line 53 is the originating bug, so that would be:
> > 
> >  47         if (type == JUMP_LABEL_ENABLE) {
> >  48                 /*
> >  49                  * We are enabling this jump label. If it is not a nop
> >  50                  * then something must have gone wrong.
> >  51                  */
> >  52                 if (unlikely(memcmp((void *)entry->code, ideal_nop, 5) != 0))
> >  53                         bug_at((void *)entry->code, __LINE__);
> > 
> > But it is a NOP isn't it? The code is
> > 
> > Unexpected op at trace_clock_global+0x6b/0x120 [ffffffff8113a21b] (0f 1f 44 00 00) 53
> > 
> > Perhaps the ideal_nop has not been set yet?
> > 
> 
> And this looks to fix it for me.

I'm trying to understand how this will fix it for you. Are you sure you
removed 'xen_nopvspin'?

If you are calling static_key_slow_inc() before jump_label_init(), then
it should still fail. The static_key_slow_inc() eventually calls
arch_jump_label_transform(), which calls __jump_label_transform() with
init == 0.

The below code looks to me that it would still compare the contents
with the ideal_nop, which hasn't been set yet.

-- Steve

> 
> diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c
> index ee11b7d..d688348 100644
> --- a/arch/x86/kernel/jump_label.c
> +++ b/arch/x86/kernel/jump_label.c
> @@ -44,13 +44,20 @@ static void __jump_label_transform(struct jump_entry *entry,
>  	union jump_code_union code;
>  	const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];
>  
> +	if (init) {
> +		const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
> +		if (unlikely(memcmp((void *)entry->code, default_nop, 5) != 0))
> +			bug_at((void *)entry->code, __LINE__);
> +	}
>  	if (type == JUMP_LABEL_ENABLE) {
>  		/*
>  		 * We are enabling this jump label. If it is not a nop
>  		 * then something must have gone wrong.
>  		 */
> -		if (unlikely(memcmp((void *)entry->code, ideal_nop, 5) != 0))
> -			bug_at((void *)entry->code, __LINE__);
> +		if (!init) {
> +			if (unlikely(memcmp((void *)entry->code, ideal_nop, 5) != 0))
> +				bug_at((void *)entry->code, __LINE__);
> +		}
>  
>  		code.jump = 0xe9;
>  		code.offset = entry->target -
> @@ -62,11 +69,7 @@ static void __jump_label_transform(struct jump_entry *entry,
>  		 * If this is the first initialization call, then we
>  		 * are converting the default nop to the ideal nop.
>  		 */
> -		if (init) {
> -			const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
> -			if (unlikely(memcmp((void *)entry->code, default_nop, 5) != 0))
> -				bug_at((void *)entry->code, __LINE__);
> -		} else {
> +		if (!init) {
>  			code.jump = 0xe9;
>  			code.offset = entry->target -
>  				(entry->code + JUMP_LABEL_NOP_SIZE);

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