Re: 2.6.17-rc6-mm1/pktcdvd - BUG: possible circular locking

[Jens Axboe]

On Mon, Jun 12 2006, Arjan van de Ven wrote:
> Laurent Riffard wrote:
> >Hello,
> >
> >This BUG happened while pktcdvd service was starting. 
> >Basically, the 2 following commands were issued:
> >- modprobe ptkcdvd
> >- pktsetup dvd /dev/dvd
> 
> This appears to be a real bug:
> 
> A normal pkt dvd block dev open takes the
> bdev_mutex in the regular block device open path, which takes
> ctl_mutex in the pkt_open function which gets called then from
> the block layer.
> 
> HOWEVER the IOCTL path does it the other way around:
> 
>                 mutex_lock(&ctl_mutex);
>                 ret = pkt_setup_dev(&ctrl_cmd);
>                 mutex_unlock(&ctl_mutex);
> 
> where pkt_setup_dev in term calls pkt_new_dev which
> calls blkdev_get(), which takes the bdev_mutex.
> 
> Looks very much like a AB-BA deadlock to me...

I'd say you are right, however I haven't touched that code since 2.5 I
think - CC'ing Peter for a fix!

-- 
Jens Axboe

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