[ofa-general] Re: [PATCH 08 of 11] anon-vma-rwsem

[Robin Holt]

On Wed, May 07, 2008 at 05:03:30PM -0700, Linus Torvalds wrote:
> 
> 
> On Wed, 7 May 2008, Christoph Lameter wrote:
> > 
> > Multiple vmas may share the same mapping or refer to the same anonymous 
> > vma. The above code will deadlock since we may take some locks multiple 
> > times.
> 
> Ok, so that actually _is_ a problem. It would be easy enough to also add 
> just a flag to the vma (VM_MULTILOCKED), which is still cleaner than doing 
> a vmalloc and a whole sort thing, but if this is really rare, maybe Ben's 
> suggestion of just using stop-machine is actually the right one just 
> because it's _so_ simple.

Also, stop-machine will not work if we come to the conclusion that
i_mmap_lock and anon_vma->lock need to be sleepable locks.

Thanks,
Robin Holt