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

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Date:	Wed, 11 Sep 2013 10:25:45 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	"H. Peter Anvin" <hpa@...ux.intel.com>
Cc:	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>,
	Steven Rostedt <rostedt@...dmis.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

> 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.

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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