linux-kernel - Re: [Bug #13112] Oops in drain

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Date:	Tue, 28 Apr 2009 20:22:48 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
Cc:	mmx@....pl, rientjes@...gle.com, cl@...ux.com,
	penberg@...helsinki.fi, linux-kernel@...r.kernel.org,
	kernel-testers@...r.kernel.org, rjw@...k.pl,
	akpm@...ux-foundation.org
Subject: Re: [Bug #13112] Oops in drain_array

On Tue, Apr 28 2009, FUJITA Tomonori wrote:
> On Tue, 28 Apr 2009 14:43:37 +0200 (CEST)
> Bart <mmx@....pl> wrote:
> 
> > > On Mon, 27 Apr 2009 13:36:46 -0700 (PDT)
> > > David Rientjes <rientjes@...gle.com> wrote:
> > >
> > >> On Mon, 27 Apr 2009, Bart wrote:
> > >>
> > >>> After turning the suggested debuging options I've got tons of these when
> > >>> trying to stress the tape device like before:
> > >>>
> > >>> Apr 27 16:57:30 fs kernel: [   96.446708] slab error in verify_redzone_free():
> > >>> cache `size-128': memory outside object was overwritten
> > >>> Apr 27 16:57:30 fs kernel: [   96.446713] Pid: 0, comm: swapper Not tainted
> > >>> 2.6.29.1-64 #2
> > >>> Apr 27 16:57:30 fs kernel: [   96.446715] Call Trace:
> > >>> Apr 27 16:57:30 fs kernel: [   96.446717]  <IRQ>  [<ffffffff8029adc5>]
> > >>> __slab_error+0x1f/0x25
> > >>> Apr 27 16:57:30 fs kernel: [   96.446728]  [<ffffffff8029b24b>]
> > >>> cache_free_debugcheck+0x108/0x1d6
> > >>> Apr 27 16:57:30 fs kernel: [   96.446731]  [<ffffffff8029b473>]
> > >>> kfree+0x81/0xc2
> > >>> Apr 27 16:57:30 fs kernel: [   96.446735]  [<ffffffff802bd311>]
> > >>> bio_free_map_data+0xc/0x1e
> > >>
> > >> This appears to be kfree(bmd->iovecs) in bio_free_map_data().  It looks
> > >> like the memcpy size in bio_set_map_data() overrides the kmalloc size; in
> > >> other words, for a redzone error, bio->bi_vcnt > nr_pages in
> > >> bio_copy_user_iov().
> > >
> > > Can you try this?
> > >
> > > diff --git a/fs/bio.c b/fs/bio.c
> > > index 7bbc98f..6a09356 100644
> > > --- a/fs/bio.c
> > > +++ b/fs/bio.c
> > > @@ -817,6 +817,9 @@ struct bio *bio_copy_user_iov(struct request_queue *q,
> > > 		len += iov[i].iov_len;
> > > 	}
> > >
> > > +	if (offset)
> > > +		nr_pages += 1;
> > > +
> > > 	bmd = bio_alloc_map_data(nr_pages, iov_count, gfp_mask);
> > > 	if (!bmd)
> > > 		return ERR_PTR(-ENOMEM);
> > >
> > 
> > There are no more errors in the dmesg after applying this patch to 
> > 2.6.29.2.
> > 
> > Without this patch I can reproduce this kind of errors on 
> > 2.6.29.1, 2.6.29.2.
> > 
> > I've not tested this patch with 2.6.29.1 and 2.6.30rc3-git3.
> > I will try to reproduce the error on 2.6.30rc3-git3 as soon as I compile 
> > it.
> 
> Thanks for testing! And very sorry about the bug.
> 
> I'm sure that you hit the same bug with 2.6.30-rc3-git.
> 
> Jens, can you please apply this against 2.6.30-rc (and we need this
> for 2.6.29.x too)?
> 
> I know that bio_copy_user_iov() is hacky. I'll try to clean up the
> mapping API later.

I'll apply it for 2.6.30-rc and CC stable. bio_copy_user_iov() is indeed
not pretty, both the API and the implementation needs looking at...

-- 
Jens Axboe

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