On Wed, 18 Jun 2008 10:13:49 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:

quoted text
> +	if (!page_cache_get_speculative())
> +		goto out;
This is obviously buggy....sorry..quilt refresh miss..

==
In speculative page cache lookup protocol, page_count(page) is set to 0
while radix-tree modification is going on, truncation, migration, etc...

While page migration, a page fault to page under migration should wait
unlock_page() and migration_entry_wait() waits for the page from its
pte entry. It does get_page() -> wait_on_page_locked() -> put_page() now.

In page migration, page_freeze_refs() -> page_unfreeze_refs() is called.

Here, page_unfreeze_refs() expects page_count(page) == 0 and panics
if page_count(page) != 0. To avoid this, we shouldn't touch page_count()
if it is zero. This patch uses page_cache_get_speculative() to avoid
the panic.

From: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
 mm/migrate.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Index: test-2.6.26-rc5-mm3/mm/migrate.c
===================================================================
--- test-2.6.26-rc5-mm3.orig/mm/migrate.c
+++ test-2.6.26-rc5-mm3/mm/migrate.c
@@ -243,7 +243,8 @@ void migration_entry_wait(struct mm_stru
 
 	page = migration_entry_to_page(entry);
 
-	get_page(page);
+	if (!page_cache_get_speculative(page))
+		goto out;
 	pte_unmap_unlock(ptep, ptl);
 	wait_on_page_locked(page);
 	put_page(page);

--
unsubscribe notice
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/