linux-kernel - Re: Kernel oops (bug) in fs/buffers.c:create_empty

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Message-ID: <20080709224637.GA30008@atrey.karlin.mff.cuni.cz>
Date:	Thu, 10 Jul 2008 00:46:37 +0200
From:	Jan Kara <jack@...e.cz>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Arjan van de Ven <arjan@...radead.org>,
	linux-kernel@...r.kernel.org, Al Viro <viro@...IV.linux.org.uk>
Subject: Re: Kernel oops (bug) in fs/buffers.c:create_empty_buffers

> On Sun, 6 Jul 2008 13:23:02 -0700 Arjan van de Ven <arjan@...radead.org> wrote:
> > Hi,
> > 
> > caught this one on kerneloops.org: 
> > http://www.kerneloops.org/searchweek.php?search=create_empty_buffers
> > 
> > void create_empty_buffers(struct page *page,
> >                         unsigned long blocksize, unsigned long b_state)
> > {
> >         struct buffer_head *bh, *head, *tail;
> > 
> >         head = alloc_page_buffers(page, blocksize, 1);
> >         bh = head;
> >         do {
> >                 bh->b_state |= b_state;
> >                 tail = bh;
> >                 bh = bh->b_this_page;
> >         } while (bh);
> > 
> > 
> > turns out, alloc_page_buffers() can fail and return NULL (for AIO for
> > example)... yet this code blindly dereferences the result, getting a
> > predictable NULL pointer fault.
> > 
> > It's not directly clear what to do about... make this function return
> > the failure to the caller?
> 
> isofs has a habit of returning impossible block sizes and the
> 
> 	while ((offset -= size) >= 0) {
> 
> consequently loops zero times and alloc_page_buffers() returns null.
> 
> Someone was having a look at it - maybe Jan?
  Yes, I was looking at that. Actually, I've pinpointed the cause of
the Oopses I've seen to a bug in ide-cd driver. It happily sets blocksize
to whatever value the drive reported and some drives have a habit of
reporting bogus values when unreadable medium is inserted.
  Jens has actually cooked up a fix for this bug
(http://thread.gmane.org/gmane.linux.kernel/696582) and it fixes the
problem at least for me.

> I assume that the kernloops.org records link back to the original
> report somewhere but I can't find it?

								Honza
-- 
Jan Kara <jack@...e.cz>
SuSE CR Labs
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