Re: [PATCH -alternative] mm: hugetlbfs: Close race during teardownof hugetlbfs shared page tables V2 (resend)

[Larry Woodman]

On 07/26/2012 01:42 PM, Rik van Riel wrote:
> On 07/23/2012 12:04 AM, Hugh Dickins wrote:
>
> > Please don't be upset if I say that I don't like either of your patches.
> > Mainly for obvious reasons - I don't like Mel's because anything with
> > trylock retries and nested spinlocks worries me before I can even start
> > to think about it; and I don't like Michal's for the same reason as Mel,
> > that it spreads more change around in common paths than we would like.
>
> I have a naive question.
>
> In huge_pmd_share, we protect ourselves by taking
> the mapping->i_mmap_mutex.
>
> Is there any reason we could not take the i_mmap_mutex
> in the huge_pmd_unshare path?

I think it is already taken on every path into huge_pmd_unshare().

Larry
> I see that hugetlb_change_protection already takes that
> lock. Is there something preventing __unmap_hugepage_range
> from also taking mapping->i_mmap_mutex?
>
> That way the sharing and the unsharing code are
> protected by the same, per shm segment, lock.

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