Re: [Bug #13112] Oops in drain_array

Jens Axboe
2009-04-28T18:22:48Z

On Tue, Apr 28 2009, FUJITA Tomonori wrote:
> On Tue, 28 Apr 2009 14:43:37 +0200 (CEST)
> Bart <mmx-G/jkD+u3s4s@public.gmane.org> wrote:
>
> > > On Mon, 27 Apr 2009 13:36:46 -0700 (PDT)
> > > David Rientjes <rientjes-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org> 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