[3.11.y.z extended stable] Patch "ftrace/x86: One more missing sync after fixup of function modification failure" has been added to staging queue

[Luis Henriques]

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

    ftrace/x86: One more missing sync after fixup of function modification failure

to the linux-3.11.y-queue branch of the 3.11.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-3.11.y-queue

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

For more information about the 3.11.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From e86049813677c9c4a71c02372d1f47390bb86f94 Mon Sep 17 00:00:00 2001
From: Petr Mladek <pmladek at suse.cz>
Date: Mon, 24 Feb 2014 17:12:20 +0100
Subject: ftrace/x86: One more missing sync after fixup of function
 modification failure

commit 12729f14d8357fb845d75155228b21e76360272d upstream.

If a failure occurs while modifying ftrace function, it bails out and will
remove the tracepoints to be back to what the code originally was.

There is missing the final sync run across the CPUs after the fix up is done
and before the ftrace int3 handler flag is reset.

Here's the description of the problem:

	CPU0				CPU1
	----				----
  remove_breakpoint();
  modifying_ftrace_code = 0;

				[still sees breakpoint]
				<takes trap>
				[sees modifying_ftrace_code as zero]
				[no breakpoint handler]
				[goto failed case]
				[trap exception - kernel breakpoint, no
				 handler]
				BUG()

Link: http://lkml.kernel.org/r/1393258342-29978-2-git-send-email-pmladek@suse.cz

Fixes: 8a4d0a687a5 "ftrace: Use breakpoint method to update ftrace caller"
Acked-by: Frederic Weisbecker <fweisbec at gmail.com>
Acked-by: H. Peter Anvin <hpa at linux.intel.com>
Signed-off-by: Petr Mladek <pmladek at suse.cz>
Signed-off-by: Steven Rostedt <rostedt at goodmis.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 arch/x86/kernel/ftrace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index e625319..1ffc32d 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -659,8 +659,8 @@ ftrace_modify_code(unsigned long ip, unsigned const char *old_code,
 		ret = -EPERM;
 		goto out;
 	}
-	run_sync();
  out:
+	run_sync();
 	return ret;

  fail_update:
--
1.9.1