Re: 2.6.15 OOPS while trying to mount cdrom

[Chuck Ebbert]

In-Reply-To: <20060110184624.GA6721@xxxxxxxxxxxxx>

On Tue, 10 Jan 2006 Helge Hafting wrote:

> Kernel 2.6.15 amd64, gcc 4.1.0 from debian.
>
> The cdrom (/dev/hda) is usually fine.  I tried booting with
> hda=ide-scsi in order to read a scratched audio cd with cdparanoia.
> That way, I at least get error messages when the scratches are
> too bad.
> 
> I forgot about hda=ide-scsi, and tried to mount /dev/hda as
> usual in order to read an ordinary iso9660 cd.  This is
> probably not supposed to work when ide-scsi is using the device,
> but then I expect something like EBUSY rather than this oops:
> 
> ide-scsi: unsup command: dev hda: flags = REQ_SORTED REQ_CMD REQ_STARTED 
> REQ_ELVPRIV 
> sector 64, nr/cnr 2/2
> bio ffff8100044a9b40, biotail ffff8100044a9b40, buffer ffff81000cb4d000, data 
> 0000000000000000, len 0
> end_request: I/O error, dev hda, sector 64
> isofs_fill_super: bread failed, dev=hda, iso_blknum=16, block=32
> Unable to handle kernel NULL pointer dereference at 0000000000000000 RIP: 
> <ffffffff80235a92>{strlen+2}


The IDE driver probably shouldn't have allowed the bdev to be opened in
the first place.

After that happened, mount attempted to fill the superblock and the I/O
failed.  Upon failure, get_sb_bdev() called deactivate_super()
(fs/super.c line 718) and all hell broke loose.

        - deactivate_super() called fs->kill_sb() (super.c line 176) which
          pointed to kill_block_super() (fs/isofs/inode.c line 1411)

        - kill_block_super() called kobject_uevent() with action KOBJ_UMOUNT
          (Question: why is it sending UMOUNT for a mount that never happened?)

        - kobject_uevent() called kobject_get_path() and one of the objects
          had a null kobject.name, which caused strlen() to oops.

There seem to be several bugs here:

(1) IDE shouldn't have allowed the bdev to be opened.

(2) (maybe) kobject_uevent shouldn't have been called for an unmount event
    when the mount never succeeded.

(3) kobject_get_path() shouldn't oops when a path component has a NULL name,
    or else kobject should fail registration of any such object.


> The pc didn't seem to malfunction after this.

If you attempt to mount the CD a second time, mount will hang in D state; ps(1)
reports it's at text.lock.super.  System cannot be cleanly shut down after that --
shutdown(8) hangs and so does sync(1).


-- 
Chuck
Currently reading: _Olympos_ by Dan Simmons
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