linux-kernel - [PATCH 3.2 109/200] compiler/gcc4: Make quirk for asm_volatile

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Message-ID: <lsq.1396221815.407981720@decadent.org.uk>
Date:	Mon, 31 Mar 2014 00:23:35 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Jakub Jelinek" <jakub@...hat.com>,
	"Ingo Molnar" <mingo@...nel.org>,
	"Richard Henderson" <rth@...ddle.net>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Steven Noonan" <steven@...inklabs.net>,
	"Peter Zijlstra" <peterz@...radead.org>,
	"Oleg Nesterov" <oleg@...hat.com>,
	"Steven Rostedt" <rostedt@...dmis.org>
Subject: [PATCH 3.2 109/200] compiler/gcc4: Make quirk for asm_volatile_goto()
 unconditional

3.2.56-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Steven Noonan <steven@...inklabs.net>

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@...ux-foundation.org>
Signed-off-by: Steven Noonan <steven@...inklabs.net>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Jakub Jelinek <jakub@...hat.com>
Cc: Richard Henderson <rth@...ddle.net>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Oleg Nesterov <oleg@...hat.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@...nel.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 include/linux/compiler-gcc4.h | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

--- a/include/linux/compiler-gcc4.h
+++ b/include/linux/compiler-gcc4.h
@@ -39,11 +39,7 @@
  *
  * (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)
 
 #if __GNUC_MINOR__ >= 5
 /*

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