LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Andi Kleen <andi@firstfloor.org>
To: Chuck Ebbert <cebbert@redhat.com>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
	Ingo Molnar <mingo@elte.hu>, Gerd Hoffmann <kraxel@redhat.com>
Subject: Re: The SMP alternatives code breaks exception fixup?
Date: 22 Jan 2008 06:26:03 +0100	[thread overview]
Message-ID: <p73zluymnx0.fsf@crumb.suse.de> (raw)
In-Reply-To: <479504F6.4080005@redhat.com>

Chuck Ebbert <cebbert@redhat.com> writes:
> 
> There is a fixup, so this should never happen. But the lock instruction
> was replaced with a nop by the altinstruction code, and that makes the fixup
> address wrong. AFAICT we don't fix up the exception table when we replace
> a lock with a nop, which makes the fixup table point to the nop instead
> of the cmpxchg instruction and causes us to miss the fixup.

Indeed.  Nasty issue.

A quick fix would be to add another fixup to handle both cases
I checked the other LOCK_PREFIX users and they look ok.

Does this fix it?

-Andi

(untested) 

---

Add exception handlers for both the LOCK and no LOCK prefix
case in futex.

Hopefully fixes https://bugzilla.redhat.com/show_bug.cgi?id=429412

Signed-off-by: Andi Kleen <ak@suse.de>

Index: linux/include/asm-x86/futex.h
===================================================================
--- linux.orig/include/asm-x86/futex.h
+++ linux/include/asm-x86/futex.h
@@ -30,7 +30,7 @@
 "1:	movl	%2, %0\n					\
 	movl	%0, %3\n"					\
 	insn "\n"						\
-"2:	" LOCK_PREFIX "cmpxchgl %3, %2\n			\
+"2:	" LOCK_PREFIX "\n5: cmpxchgl %3, %2\n			\
 	jnz	1b\n						\
 3:	.section .fixup,\"ax\"\n				\
 4:	mov	%5, %1\n					\
@@ -38,7 +38,7 @@
 	.previous\n						\
 	.section __ex_table,\"a\"\n				\
 	.align	8\n"						\
-	_ASM_PTR "1b,4b,2b,4b\n					\
+	_ASM_PTR "1b,4b,2b,4b,5b,4b\n				\
 	.previous"						\
 	: "=&a" (oldval), "=&r" (ret), "+m" (*uaddr),		\
 	  "=&r" (tem)						\

  parent reply	other threads:[~2008-01-22  5:26 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-01-21 20:47 Chuck Ebbert
2008-01-21 21:25 ` Chuck Ebbert
2008-01-22  5:26 ` Andi Kleen [this message]
2008-01-22 12:35   ` Thomas Gleixner
2008-01-22 20:19     ` Chuck Ebbert
2008-02-06 23:10       ` [stable] " Greg KH
2008-02-06 23:36         ` Linus Torvalds
2008-02-06 23:43           ` Ingo Molnar
2008-02-07  0:00             ` Greg KH
2008-02-07  6:55             ` Greg KH
2008-02-07 12:16         ` Thomas Gleixner

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=p73zluymnx0.fsf@crumb.suse.de \
    --to=andi@firstfloor.org \
    --cc=cebbert@redhat.com \
    --cc=kraxel@redhat.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@elte.hu \
    --subject='Re: The SMP alternatives code breaks exception fixup?' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).