[3.8.y.z extended stable] Patch "compiler/gcc4: Make quirk for asm_volatile_goto() unconditional" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    compiler/gcc4: Make quirk for asm_volatile_goto() unconditional

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.19.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 38faf88de86048216c000cac3dcafe340fb0b713 Mon Sep 17 00:00:00 2001
From: Steven Noonan <steven at uplinklabs.net>
Date: Wed, 12 Feb 2014 23:01:07 -0800
Subject: compiler/gcc4: Make quirk for asm_volatile_goto() unconditional

commit a9f180345f5378ac87d80ed0bea55ba421d83859 upstream.

I started noticing problems with KVM guest destruction on Linux
3.12+, where guest memory wasn't being cleaned up. I bisected it
down to the commit introducing the new 'asm goto'-based atomics,
and found this quirk was later applied to those.

Unfortunately, even with GCC 4.8.2 (which ostensibly fixed the
known 'asm goto' bug) I am still getting some kind of
miscompilation. If I enable the asm_volatile_goto quirk for my
compiler, KVM guests are destroyed correctly and the memory is
cleaned up.

So make the quirk unconditional for now, until bug is found
and fixed.

Suggested-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Steven Noonan <steven at uplinklabs.net>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Steven Rostedt <rostedt at goodmis.org>
Cc: Jakub Jelinek <jakub at redhat.com>
Cc: Richard Henderson <rth at twiddle.net>
Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Oleg Nesterov <oleg at redhat.com>
Link: http://lkml.kernel.org/r/1392274867-15236-1-git-send-email-steven@uplinklabs.net
Link: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58670
Signed-off-by: Ingo Molnar <mingo at kernel.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 include/linux/compiler-gcc4.h | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/include/linux/compiler-gcc4.h b/include/linux/compiler-gcc4.h
index e8f0bf9..a11c184 100644
--- a/include/linux/compiler-gcc4.h
+++ b/include/linux/compiler-gcc4.h
@@ -77,11 +77,7 @@
  *
  * (asm goto is automatically volatile - the naming reflects this.)
  */
-#if GCC_VERSION <= 40801
-# define asm_volatile_goto(x...)	do { asm goto(x); asm (""); } while (0)
-#else
-# define asm_volatile_goto(x...)	do { asm goto(x); } while (0)
-#endif
+#define asm_volatile_goto(x...)	do { asm goto(x); asm (""); } while (0)

 #ifdef CONFIG_ARCH_USE_BUILTIN_BSWAP
 #if __GNUC_MINOR__ >= 4
--
1.8.3.2