[PATCH] lockdep fix incorrect percpu usage

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

Should use per_cpu_ptr() to obfuscate the per cpu pointers (RELOC_HIDE is needed
for per cpu pointers).

git blame points to commit:

lockdep.c: commit 8e18257d29238311e82085152741f0c3aa18b74d

But it's really just moving the code around. But it's enough to say that the
problems appeared before Jul 19 01:48:54 2007, which brings us back to 2.6.23.

So it should be applied to stable 2.6.23.x to 2.6.33.x (or whichever of these
stable branches are still maintained) and to mainline 2.6.34-rc2.

This patch should be queued for the stable branch.
(tested on 2.6.33.1 x86_64)

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
CC: Randy Dunlap <randy.dunlap@oracle.com>
CC: Eric Dumazet <dada1@cosmosbay.com>
CC: Rusty Russell <rusty@rustcorp.com.au>
CC: Peter Zijlstra <a.p.zijlstra@chello.nl>
CC: Tejun Heo <tj@kernel.org>
CC: Ingo Molnar <mingo@elte.hu>
CC: Andrew Morton <akpm@linux-foundation.org>
CC: Linus Torvalds <torvalds@linux-foundation.org>
CC: Greg Kroah-Hartman <gregkh@suse.de>
CC: Steven Rostedt <rostedt@goodmis.org>
CC: stable <stable@kernel.org>
---
 kernel/lockdep.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Index: linux-2.6-lttng/kernel/lockdep.c
===================================================================
--- linux-2.6-lttng.orig/kernel/lockdep.c	2010-03-29 23:54:31.000000000 -0400
+++ linux-2.6-lttng/kernel/lockdep.c	2010-03-29 23:54:38.000000000 -0400
@@ -609,9 +609,9 @@ static int static_obj(void *obj)
 	 * percpu var?
 	 */
 	for_each_possible_cpu(i) {
-		start = (unsigned long) &__per_cpu_start + per_cpu_offset(i);
-		end   = (unsigned long) &__per_cpu_start + PERCPU_ENOUGH_ROOM
-					+ per_cpu_offset(i);
+		start = (unsigned long) per_cpu_ptr(&__per_cpu_start, i);
+		end   = (unsigned long) per_cpu_ptr(&__per_cpu_start
+						    + PERCPU_ENOUGH_ROOM, i);
 
 		if ((addr >= start) && (addr < end))
 			return 1;

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com