Re: [PATCH v4] mm: per-thread vma caching

[Davidlohr Bueso]

On Sat, 2014-03-08 at 12:02 -0800, Linus Torvalds wrote:
> On Sat, Mar 8, 2014 at 11:44 AM, Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
> >
> > Sure. But another thread or CLONE_VM task can do vmacache_invalidate(),
> > hit vmacache_seqnum == 0 and call vmacache_flush_all() to solve the
> > problem with potential overflow.
> 
> How?
> 
> Any invalidation is supposed to hold the mm semaphore for writing. And
> we should have it for reading.

Yes, invalidations are always with the write lock held. In any case it's
a good candidate to use verify_mm_writelocked(), even if it's only under
debug environments.

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