Re: [stable] [PATCH] lockdep fix incorrect percpu usage

Mathieu Desnoyers
2010-04-20T14:33:54Z

* Greg KH (greg@kroah.com) wrote:
> On Wed, Mar 31, 2010 at 11:43:16AM +0900, Tejun Heo wrote:
> > On 03/31/2010 12:05 AM, Mathieu Desnoyers wrote:
> > > I see. These patches are "on their way" to mainline, so it's better not to
> > > create conflicts. So the lockdep patch should only be applied to -stable, but
> > > separate module.c patch should apply to both -stable and mainline. Am I
> > > correct ?
> >
> > I'll push proper fixes to mainline in a few days. For -stable, yeah,
> > probably.
>
> Ok, did a patch ever end up in Linus's tree for this that I can pull
> into the -stable releases?
>
> thanks,
>
> greg k-h

Hi Greg,

Here is the updated patch, stating which mainline commit from Tejun fixes it by
refactoring the code. I'll leave the decision to pick this targeted fix or Tejun
refactoring into -stable up to you.

lockdep fix incorrect percpu usage

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.

It should be applied to stable 2.6.23.x to 2.6.33.x (or whichever of these
stable branches are still maintained).

The mainline kernel as of 2.6.34-rc5 is not affected by this problem because
commit 10fad5e46f6c7bdfb01b1a012380a38e3c6ab346 fixed it by refactoring.

(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.trees.git/kernel/lockdep.c
===================================================================
--- linux.trees.git.orig/kernel/lockdep.c 2010-03-19 16:18:34.000000000 -0400
+++ linux.trees.git/kernel/lockdep.c 2010-03-30 09:48:43.000000000 -0400
@@ -600,9 +600,9 @@ 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.