Re: [PATCH 1/2] mm,migration: Prevent rmap_walk_[anon|ksm] seeingthe wrong VMA information

[Rik van Riel]

On 05/05/2010 01:34 PM, Linus Torvalds wrote:

>   - you always lock the _deepest_ anon_vma you can find.

The emphasis should be on "always" :)

> That means just a single lock. And the "deepest" anon_vma is well-defined
> for all anon_vma's, because each same_anon_vma chain is always rooted in
> the original anon_vma that caused it.

It should work, but only if we always take the deepest
anon_vma lock.

Not just in the migration code, but also in mmap, munmap,
mprotect (for split_vma), expand_stack, etc...

Otherwise we will still not provide exclusion of migrate
vs. those events.

I'm guessing that means changing both anon_vma_lock and
page_lock_anon_vma to always take the deepest anon_vma
lock - not introducing a new function that is only called
by the migration code.

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