From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx172.postini.com [74.125.245.172]) by kanga.kvack.org (Postfix) with SMTP id 25F7E6B004D for ; Mon, 5 Nov 2012 20:32:47 -0500 (EST) Received: by mail-ie0-f169.google.com with SMTP id 10so11318678ied.14 for ; Mon, 05 Nov 2012 17:32:46 -0800 (PST) Date: Mon, 5 Nov 2012 17:32:41 -0800 (PST) From: Hugh Dickins Subject: [PATCH] tmpfs: fix shmem_getpage_gfp VM_BUG_ON In-Reply-To: Message-ID: References: <20121025023738.GA27001@redhat.com> <20121101191052.GA5884@redhat.com> <20121101232030.GA25519@redhat.com> <20121102014336.GA1727@redhat.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Dave Jones , Johannes Weiner , linux-mm@kvack.org, linux-kernel@vger.kernel.org Fuzzing with trinity hit the "impossible" VM_BUG_ON(error) (which Fedora has converted to WARNING) in shmem_getpage_gfp(): WARNING: at mm/shmem.c:1151 shmem_getpage_gfp+0xa5c/0xa70() Pid: 29795, comm: trinity-child4 Not tainted 3.7.0-rc2+ #49 Call Trace: [] warn_slowpath_common+0x7f/0xc0 [] warn_slowpath_null+0x1a/0x20 [] shmem_getpage_gfp+0xa5c/0xa70 [] shmem_fault+0x4f/0xa0 [] __do_fault+0x71/0x5c0 [] handle_pte_fault+0x97/0xae0 [] handle_mm_fault+0x289/0x350 [] __do_page_fault+0x18e/0x530 [] do_page_fault+0x2b/0x50 [] page_fault+0x28/0x30 [] tracesys+0xe1/0xe6 Thanks to Johannes for pointing to truncation: free_swap_and_cache() only does a trylock on the page, so the page lock we've held since before confirming swap is not enough to protect against truncation. What cleanup is needed in this case? Just delete_from_swap_cache(), which takes care of the memcg uncharge. Reported-by: Dave Jones Hypothesis-by: Johannes Weiner Signed-off-by: Hugh Dickins Cc: stable@vger.kernel.org --- mm/shmem.c | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-) --- 3.7-rc4/mm/shmem.c 2012-10-14 16:16:58.361309122 -0700 +++ linux/mm/shmem.c 2012-11-01 14:31:04.288185742 -0700 @@ -1145,8 +1145,22 @@ repeat: if (!error) { error = shmem_add_to_page_cache(page, mapping, index, gfp, swp_to_radix_entry(swap)); - /* We already confirmed swap, and make no allocation */ - VM_BUG_ON(error); + /* + * We already confirmed swap under page lock, and make + * no memory allocation here, so usually no possibility + * of error; but free_swap_and_cache() only trylocks a + * page, so it is just possible that the entry has been + * truncated or holepunched since swap was confirmed. + * shmem_undo_range() will have done some of the + * unaccounting, now delete_from_swap_cache() will do + * the rest (including mem_cgroup_uncharge_swapcache). + * Reset swap.val? No, leave it so "failed" goes back to + * "repeat": reading a hole and writing should succeed. + */ + if (error) { + VM_BUG_ON(error != -ENOENT); + delete_from_swap_cache(page); + } } if (error) goto failed; -- 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