Re: md deadlock (was Re: 2.6.18-mm2)

Peter Zijlstra
2006-10-02T13:48:03Z

On Fri, 2006-09-29 at 16:03 +0200, Peter Zijlstra wrote:
> On Fri, 2006-09-29 at 22:52 +1000, Neil Brown wrote:
> > On Friday September 29, a.p.zijlstra@chello.nl wrote:
> > > On Thu, 2006-09-28 at 13:54 +0200, Michal Piotrowski wrote:
> > >
> > > Looks like a real deadlock here. It seems to me #2 is the easiest to
> > > break.
> >
> > I guess it could deadlock if you tried to add /dev/md0 as a component
> > of /dev/md0. I should probably check for that somewhere.
> > In other cases the array->member ordering ensures there is no
> > deadlock.
> >
>
>
> 1 2
>
> open(/dev/md0)
>
> open(/dev/md0)
> - do_open() -> bdev->bd_mutex
> ioctl(/dev/md0, hotadd)
> - md_ioctl() -> mddev->reconfig_mutex
> -- hot_add_disk()
> --- bind_rdev_to_array()
> ---- bd_claim_by_disk()
> ----- bd_claim_by_kobject()
> -- md_open()
> --- mddev_lock()
> ---- mutex_lock(mddev->reconfig_mutex)
> ------ mutex_lock(bdev->bd_mutex)
>

D'0h, 1:bdev->bd_mutex is ofcourse rdev->bd_mutex; the slave device's
mutex.

So mddev->bd_mutex wants to be another class all-together.