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

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Date:	Mon, 02 Oct 2006 15:47:38 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Neil Brown <neilb@...e.de>
Cc:	Michal Piotrowski <michal.k.k.piotrowski@...il.com>,
	Andrew Morton <akpm@...l.org>, Ingo Molnar <mingo@...e.hu>,
	linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: md deadlock (was Re: 2.6.18-mm2)

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@...llo.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. 

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