linux-kernel - Re: [origin tree SLAB corruption] BUG kmalloc-64: Poison overwritten, INFO: Allocated in bdi_alloc

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Date:	Mon, 14 Sep 2009 09:29:02 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Eric Paris <eparis@...hat.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Jens Axboe <jens.axboe@...cle.com>,
	James Morris <jmorris@...ei.org>, Thomas Liu <tliu@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [origin tree SLAB corruption] BUG kmalloc-64: Poison
	overwritten, INFO: Allocated in bdi_alloc_work+0x2b/0x100 age=175
	cpu=1 pid=3514

On Mon, Sep 14, 2009 at 07:40:27AM -0700, Linus Torvalds wrote:
> 
> 
> On Mon, 14 Sep 2009, Ingo Molnar wrote:
> > 
> > BUG kmalloc-64: Poison overwritten
> > -----------------------------------------------------------------------------
> > 
> > INFO: 0xf498f6a0-0xf498f6a7. First byte 0x90 instead of 0x6b
> > INFO: Allocated in bdi_alloc_work+0x2b/0x100 age=175 cpu=1 pid=3514
> > INFO: Freed in bdi_work_free+0x45/0x60 age=9 cpu=1 pid=3509
> > INFO: Slab 0xc3257d84 objects=36 used=11 fp=0xf498f690 flags=0x400000c3
> > INFO: Object 0xf498f690 @offset=1680 fp=0xf498fe00
> > 
> > Bytes b4 0xf498f680:  ab 0d 00 00 9c 27 ff ff 5a 5a 5a 5a 5a 5a 5a 5a ?....'??ZZZZZZZZ
> >   Object 0xf498f690:  6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
> >   Object 0xf498f6a0:  90 f3 98 f4 60 3c 11 c1 6b 6b 6b 6b 6b 6b 6b 6b .?.?`<.?kkkkkkkk
> 
> That's 8 bytes of 0xf498f398 and 0xc1113c60. Doesn't look like much, but 
> they're both valid kernel pointers, and the 0xf498f398 one is actually 
> into the same page as the corruption, so it's a pointer to the same slab 
> type (or at least same size). Which is a good hint in itself: we're 
> looking at a list or something.
> 
> And it's at offset 16 in the structure. 
> 
> That's almost certainly a "struct bdi_work", and the use-aftr-free thing 
> is the "struct rcu_head rcu_head" part of it. That first thing (pointer to 
> the same page) is 'next', and the second thing is a pointer to kernel text 
> (and I can pretty much guarantee that 0xc1113c60 is 'bdi_work_free').
> 
> So this is either a fs/fs-writeback.c bug, or it's a problem with RCU. 
> Both of them are new or hugely changed since 2.6.31.

If this run had used CONFIG_TREE_PREEMPT_RCU rather than the
CONFIG_TREE_RCU that it actually had used, I would suggest applying the
patchset I submitted yesterday (Sept 13).

	http://thread.gmane.org/gmane.linux.kernel/888803

Will take a look, regardless.

							Thanx, Paul
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