Race between try_to_swap_out() and swapin_readahead()

From: Marcelo Tosatti (marcelo@conectiva.com.br)
Date: Wed May 09 2001 - 12:52:28 EST

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Ok, what prevents this from happening:

CPU0 CPU1

try_to_swap_out()
...

entry = get_swap_page();
if (!entry.val)
goto out_unlock_restore;

                                swapin_readahead()
                                finds valid swap entry just allocated by try_to_swap_out()
                                lookup_swap_cache() fails...
                                new_page = alloc_page();
                                lock_page(new_page);
                                add_to_swap_cache(new_page, entry);
                                rw_swap_page(READ, new_page);
                                 return new_page;

/* Add it to the swap cache and mark it dirty */
add_to_swap_cache(page, entry);
set_page_dirty(page);

----

We'll end up with two pages with the same index in the hash tables, and one of them has crap read from swap.

I know the window is really really small, but anyway...

Comments?

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