From: Hugh Dickins <hugh@veritas.com>
To: Marcelo Tosatti <marcelo@conectiva.com.br>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>, linux-kernel@vger.kernel.org
Subject: [PATCH] swap 2/4 unsafe SwapCache check
Date: Wed, 12 Jun 2002 04:05:31 +0100 (BST) [thread overview]
Message-ID: <Pine.LNX.4.21.0206120403280.1036-100000@localhost.localdomain> (raw)
In-Reply-To: <Pine.LNX.4.21.0206120359270.1036-100000@localhost.localdomain>
Recent testing has shown that the BUG() check in try_to_unuse is unsafe.
delete_from_swap_cache does final swap_free just after removing page
from swap cache, and add_to_swap_cache does swap_duplicate just before
putting page into swap cache, therefore swapin_readahead may resurrect
a dying swap entry and assign a new page to it. That's fine, there's
no need to change this ordering; but it does mean that try_to_unuse's
page may have left the swap cache yet its swap_map count still be set.
That BUG() has done good service for swapoff sanity, but now abandon it.
--- 2.4.19-pre10/mm/swapfile.c Tue Jun 4 13:54:20 2002
+++ linux/mm/swapfile.c Tue Jun 11 19:02:30 2002
@@ -671,10 +671,7 @@
* private" pages, but they are handled by tmpfs files.
* Note shmem_unuse already deleted its from swap cache.
*/
- swcount = *swap_map;
- if ((swcount > 0) != PageSwapCache(page))
- BUG();
- if ((swcount > 1) && PageDirty(page)) {
+ if ((*swap_map > 1) && PageDirty(page) && PageSwapCache(page)) {
rw_swap_page(WRITE, page);
lock_page(page);
}
next prev parent reply other threads:[~2002-06-12 3:05 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <Pine.LNX.4.21.0206120343290.1036-100000@localhost.localdomain>
2002-06-12 2:51 ` [PATCH] tmpfs 1/4 symlink unwind Hugh Dickins
2002-06-12 2:54 ` [PATCH] tmpfs 2/4 mknod times Hugh Dickins
2002-06-12 2:56 ` [PATCH] tmpfs 3/4 partial truncate Hugh Dickins
2002-06-12 2:58 ` [PATCH] tmpfs 4/4 swapoff tweaks Hugh Dickins
2002-06-12 3:03 ` [PATCH] swap 1/4 swapon memleak Hugh Dickins
2002-06-12 3:05 ` Hugh Dickins [this message]
2002-06-12 3:08 ` [PATCH] swap 3/4 unsafe Dirty check Hugh Dickins
2002-06-12 3:11 ` [PATCH] swap 4/4 redundant SwapCache checks Hugh Dickins
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