Re: [PATCH 2/2] Futex non-page-pinning fix

[Hugh Dickins]

On Wed, 27 Aug 2003, Andrew Morton wrote:
> Hugh Dickins <hugh@xxxxxxxxxxx> wrote:
> >
> > But I disagree over move_to/from_swap_cache: nothing should
> >  be done there at all.  Once you have mapping,index in struct
> >  futex_q, it's irrelevant what tmpfs might be doing to the
> >  page->mapping,page->index of the unmapped page.
> 
> But move_to_swap_cache() alters a page's ->mapping and ->index when that
> page is potentially mapped into user pagetables.

It'd better not: BUG_ON(page_mapped(page)) at start of shmem_writepage,
sole caller of move_to_swap_cache.  Things fall apart if tmpfs pages
get reassigned to swap while they're mapped.

Hugh

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