From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Wed, 18 Jun 2008 10:13:49 +0900 From: KAMEZAWA Hiroyuki Subject: Re: [PATCH][RFC] fix kernel BUG at mm/migrate.c:719! in 2.6.26-rc5-mm3 Message-Id: <20080618101349.db4d5205.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20080617163501.7cf411ee.nishimura@mxp.nes.nec.co.jp> References: <20080611225945.4da7bb7f.akpm@linux-foundation.org> <20080617163501.7cf411ee.nishimura@mxp.nes.nec.co.jp> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Daisuke Nishimura Cc: Andrew Morton , Rik van Riel , Lee Schermerhorn , Kosaki Motohiro , Nick Piggin , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-testers@vger.kernel.org, "hugh@veritas.com" List-ID: On Tue, 17 Jun 2008 16:35:01 +0900 Daisuke Nishimura 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 Signed-off-by: KAMEZAWA Hiroyuki --- 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, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org