Re: [RFC][PATCH 1/3] radix priority search tree - objrmap complexity fix

Andrea Arcangeli
2004-04-01T15:15:34Z

> diff -urNp --exclude CVS --exclude BitKeeper --exclude {arch} --exclude .arch-ids x-ref/mm/page_io.c x/mm/page_io.c
> --- x-ref/mm/page_io.c 2004-04-01 17:07:10.231289760 +0200
> +++ x/mm/page_io.c 2004-04-01 17:07:33.182800600 +0200
> @@ -139,7 +139,7 @@ struct address_space_operations swap_aop
>
> /*
> * A scruffy utility function to read or write an arbitrary swap page
> - * and wait on the I/O.
> + * and wait on the I/O. The caller must have a ref on the page.
> */
> int rw_swap_page_sync(int rw, swp_entry_t entry, struct page *page)
> {
> @@ -151,8 +151,16 @@ int rw_swap_page_sync(int rw, swp_entry_
> lock_page(page);
>
> BUG_ON(page->mapping);
> - page->mapping = &swapper_space;
> - page->index = entry.val;
> + ret = add_to_page_cache(page, &swapper_space, entry.val, GFP_KERNEL);
> + if (unlikely(ret)) {
> + unlock_page(page);
> + return ret;
> + }
> + /*
> + * get one more reference to make page non-exclusive so
> + * remove_exclusive_swap_page won't mess with it.
> + */
> + page_cache_get(page);
>
> if (rw == READ) {
> ret = swap_readpage(NULL, page);
> @@ -161,7 +169,13 @@ int rw_swap_page_sync(int rw, swp_entry_
> ret = swap_writepage(page, &swap_wbc);
> wait_on_page_writeback(page);
> }
> - page->mapping = NULL;
> +
> + lock_page(page);
> + remove_from_page_cache(page);
> + unlock_page(page);
> + page_cache_release(page);
> + page_cache_release(page); /* For add_to_page_cache() */
> +
> if (ret == 0 && (!PageUptodate(page) || PageError(page)))
> ret = -EIO;
> return ret;

incrementally to the above I applied this hardness checks in the
anon-vma patch, so we're safe against the problem Andrew outlined
(somebody attempting to do swapin/swapouts of anonymous pages through
that interface, something that shouldn't happen since we want only the
VM to deal with userspace mapped pages).

@@ -149,8 +149,14 @@ int rw_swap_page_sync(int rw, swp_entry_
};

lock_page(page);
-
+ /*
+ * This library call can be only used to do I/O
+ * on _private_ pages just allocated with alloc_pages().
+ */
BUG_ON(page->mapping);
+ BUG_ON(PageSwapCache(page));
+ BUG_ON(PageAnon(page));
+ BUG_ON(PageLRU(page));
ret = add_to_page_cache(page, &swapper_space, entry.val, GFP_KERNEL);
if (unlikely(ret)) {
unlock_page(page);