On Tue, 17 Jun 2008 16:35:01 +0900 Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx> wrote: > This patch also fixes a race between migrate_entry_wait and > page_freeze_refs in migrate_page_move_mapping. > Ok, let's fix one by one. please add your Signed-off-by if ok. This is a fix for page migration under speculative page lookup protocol. -Kame == In speculative page cache lookup protocol, page_count(page) is set to 0 while radix-tree midification 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@xxxxxxxxxxxxxxxxx> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> --- 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()) + goto out; pte_unmap_unlock(ptep, ptl); wait_on_page_locked(page); put_page(page); -- To unsubscribe from this list: send the line "unsubscribe kernel-testers" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
