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SubjectRe: SLOB lockup (was: Re: [tip:core/locking] lockdep: annotate reclaim context (__GFP_NOFS), fix SLOB)
Date
On Sunday 15 March 2009 17:48:18 Ingo Molnar wrote:

> > Cc: Nick Piggin <npiggin@suse.de>
> > Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
> > LKML-Reference: <20090128135457.350751756@chello.nl>
> > Signed-off-by: Ingo Molnar <mingo@elte.hu>
>
> and with this fixed, and with SLOB now being tested in -tip, the
> new lockdep assert attached below (followed by a real lockup)
> pops up.
>
> Seems like a genuine SLOB bug, probably present upstream as
> well.

Hmmf. debugobjects calls back into the slab allocator from the page
allocator. The following patch would improve SLOB, but I think it
would be a good idea to avoid a dependency in that direction. Can
debugobjects defer this freeing?

---
mm/slob.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

Index: linux-2.6/mm/slob.c
===================================================================
--- linux-2.6.orig/mm/slob.c
+++ linux-2.6/mm/slob.c
@@ -390,13 +390,14 @@ static void slob_free(void *block, int s
spin_lock_irqsave(&slob_lock, flags);

if (sp->units + units == SLOB_UNITS(PAGE_SIZE)) {
+ spin_lock_irqrestore(&slob_lock, flags);
/* Go directly to page allocator. Do not pass slob allocator */
if (slob_page_free(sp))
clear_slob_page_free(sp);
clear_slob_page(sp);
free_slob_page(sp);
free_page((unsigned long)b);
- goto out;
+ return;
}

if (!slob_page_free(sp)) {


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