linux-kernel - Re: Oops when using growisofs

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Date:	Tue, 24 Jun 2008 20:39:18 +0200
From:	Michael Buesch <mb@...sch.de>
To:	Jan Kara <jack@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Arnd Bergmann <arnd@...db.de>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Jens Axboe <axboe@...nel.dk>, Jan Kara <jack@....cz>
Subject: Re: Oops when using growisofs

On Tuesday 24 June 2008 19:28:12 Jan Kara wrote:
> > On Mon, 23 Jun 2008 00:28:20 +0200 Michael Buesch <mb@...sch.de> wrote:
> > 
> > > On Monday 23 June 2008 00:05:51 Michael Buesch wrote:
> > > > > Note: r9 and r3 are both NULL pointers. r3 is the value returned from alloc_page_buffers.
> > > > > R9 is a copy of that, which gets accessed.
> > > > 
> > > > Hm, yeah. I looked at that code already, but I can't see how it could return
> > > > a NULL pointer.
> > > 
> > > Well, actually, it can return a NULL pointer.
> > > 
> > >  928         head = NULL;
> > >  929         offset = PAGE_SIZE;
> > >  930         while ((offset -= size) >= 0) {
> > > ...
> > >  949         }
> > >  950         return head;
> > > 
> > > So if size, which is a passed in as parameter, is > PAGE_SIZE it will return NULL.
> > > 
> > > The size parameter is calculated by doing
> > > blocksize = 1 << inode->i_blkbits;
> > > in an earlier function in the callchain.
> > 
> > Yes, that's a more likely scenario.  isofs has a history of passing
> > garbage into the VFS.
> > 
> > > So, well. I dunno what i_blkbits is. There's no docs in struct inode.
> > 
> > It's log2 of the filesystem blocksize.  It'd be interesting to work out
> > what value isofs is setting it to, and why.
>   Well, yes, that looks as a reason at the first sight. But what I don't
> get is, how can isofs possibly set such a blocksize when it uses
> sb_set_blocksize() which checks whether blocksize isn't larger than page
> size... So it must be something less obvious.
>   bd_set_size() can possibly set blocksize larger than PAGE_SIZE and
> it's called from do_open() but it uses bdev_hardsect_size() and that
> shouldn't be larger than PAGE_SIZE either (at least drivers seem to take
> care of this).
>   I have seen one more report of this Oops for SLES10 kernel and also in that
> case an IO error happened so probably that is a trigger... But so far I
> don't get the details.

Yeah the IO error is the trigger.
I noticed that it had obvious troubles accessing the DVD that was in the drive.
It sweeped over it for several seconds, then hung the system for 2 or 3 seconds
and then oopsed. But after that everything continued to work as usual.
(Except kded of course)

-- 
Greetings Michael.
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