Re: [PATCH 2/5] HWPOISON: fix tasklist_lock/anon_vma locking order

[Nick Piggin <npiggin@suse.de>]

On Fri, Jun 12, 2009 at 12:03:08PM +0200, Andi Kleen wrote:
> On Thu, Jun 11, 2009 at 10:22:41PM +0800, Wu Fengguang wrote:
> > To avoid possible deadlock. Proposed by Nick Piggin:
> 
> I disagree with the description. There's no possible deadlock right now.
> It would be purely out of paranoia.
> 
> > 
> >   You have tasklist_lock(R) nesting outside i_mmap_lock, and inside anon_vma
> >   lock. And anon_vma lock nests inside i_mmap_lock.
> > 
> >   This seems fragile. If rwlocks ever become FIFO or tasklist_lock changes
> 
> I was a bit dubious on this reasoning. If rwlocks become FIFO a lot of
> stuff will likely break.
> 
> >   type (maybe -rt kernels do it), then you could have a task holding
> 
> I think they tried but backed off quickly again
> 
> It's ok with a less scare-mongering description.

There's simply no good reason to invert ordering of locks like
this.

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