Re: [Patch] shmem_unuse race fix

From: Christoph Rohland (
Date: Thu Dec 28 2000 - 07:02:07 EST

Linus Torvalds <> writes:

> On 27 Dec 2000, Christoph Rohland wrote:
> Woul dyou mind testing this alternate fix instead:

Does not work, but is the right direction I think.

First we need the following patch since otherwise we use a swap entry
without having the count increased:

--- 4-13-4/mm/vmscan.c Fri Dec 22 10:05:38 2000
+++ m4-13-4/mm/vmscan.c Thu Dec 28 11:57:57 2000
@@ -93,8 +93,8 @@
                entry.val = page->index;
                if (pte_dirty(pte))
                set_pte(page_table, swp_entry_to_pte(entry));
@@ -185,7 +185,7 @@
         * we have the swap cache set up to associate the
         * page with that swap entry.
- entry = get_swap_page();
+ entry = __get_swap_page(2);
        if (!entry.val)
                goto out_unlock_restore; /* No swap space left */

Second there look at this in handle_pte_fault:

                 * If it truly wasn't present, we know that kswapd
                 * and the PTE updates will not touch it later. So
                 * drop the lock.
                if (pte_none(entry))
                        return do_no_page(mm, vma, address, write_access, pte);
                return do_swap_page(mm, vma, address, pte, pte_to_swp_entry(entry), write_access);

The comment is wrong. try_to_unuse will touch it. This stumbles over a
bad swap entry after try_to_unuse complaining about an undead swap

If I retry in try_to_unuse it goes into an infinite loop since it
deadlocks with this.


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