Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752874Ab0HHKFW (ORCPT ); Sun, 8 Aug 2010 06:05:22 -0400 Received: from smtp.nokia.com ([192.100.122.230]:29974 "EHLO mgw-mx03.nokia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752349Ab0HHKFS (ORCPT ); Sun, 8 Aug 2010 06:05:18 -0400 Subject: Re: [PATCH 0/6] improve list_sort test From: Artem Bityutskiy Reply-To: dedekind1@gmail.com To: Don Mullis Cc: linux-kernel@vger.kernel.org, David Airlie , Dave Chinner In-Reply-To: <1281168645-18413-1-git-send-email-dedekind1@gmail.com> References: <1281168645-18413-1-git-send-email-dedekind1@gmail.com> Content-Type: text/plain; charset="UTF-8" Date: Sun, 08 Aug 2010 13:03:09 +0300 Message-ID: <1281261789.2384.11.camel@localhost> Mime-Version: 1.0 X-Mailer: Evolution 2.30.2 (2.30.2-4.fc13) Content-Transfer-Encoding: 8bit X-OriginalArrivalTime: 08 Aug 2010 10:04:50.0864 (UTC) FILETIME=[23EFA300:01CB36E1] X-Nokia-AV: Clean Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3485 Lines: 105 On Sat, 2010-08-07 at 11:10 +0300, Artem Bityutskiy wrote: > Hi, > > while hunting a non-existing bug in 'list_sort()', I've improved the > 'list_sort_test()' function which tests the 'list_sort()' library call. Although > at the end I found a bug in my code, but not in 'list_sort()', I think my > clean-ups and improvements are worth merging because they make the test function > better. Actually, your 'list_sort()' version does have a problem. I found out that it calls 'cmp(priv, a, b)' with 'a = b' sometimes, and in these cases 'a' and 'b' can point to something which is not a valid element of the original list. Probably a senitel or something like that. It is easy to work around this by adding: if (a == b) return 0; in the 'cmp()' function, but this is nevertheless a bug (not too bad, though) and should be fixed. Also, the fact that 'cmp()' is called with 'a==b' sometimes should be documented. I'm CC-ing 2 other users of 'list_sort()' for head-ups (xfs, drm). I've fixed assertions in UBIFS using the following patch: =========================================================================== >From 3ea1708e2d0462dc8eaf1076ebf973d82700952b Mon Sep 17 00:00:00 2001 From: Artem Bityutskiy Date: Sun, 8 Aug 2010 12:45:23 +0300 Subject: [PATCHv2 8/9] UBIFS: fix assertion warnings in comparison function When running the integrity test ('integck' from mtd-utils) on current UBIFS on 2.6.35, I see that assertions in UBIFS 'list_sort()' comparison functions trigger sometimes, e.g.: UBIFS assert failed in data_nodes_cmp at 132 (pid 28311) My investigation showed that this happens when 'list_sort()' calls the 'cmp()' function with equivalent arguments. In this case, the 'struct list_head' parameter, passed to 'cmp()' is bogus, and it does not belong to any element in the original list. And this issue seems to be introduced by commit: commit 835cc0c8477fdbc59e0217891d6f11061b1ac4e2 Author: Don Mullis Date: Fri Mar 5 13:43:15 2010 -0800 It is easy to work around the issue by doing: if (a == b) return 0; in UBIFS. It works, but 'lib_sort()' should nevertheless be fixed. Although it is harmless to have this piece of code in UBIFS. This patch adds that code to both UBIFS 'cmp()' functions: 'data_nodes_cmp()' and 'nondata_nodes_cmp()'. Signed-off-by: Artem Bityutskiy --- fs/ubifs/gc.c | 6 ++++++ 1 files changed, 6 insertions(+), 0 deletions(-) diff --git a/fs/ubifs/gc.c b/fs/ubifs/gc.c index 8dbe36f..84ab9aa 100644 --- a/fs/ubifs/gc.c +++ b/fs/ubifs/gc.c @@ -125,6 +125,9 @@ int data_nodes_cmp(void *priv, struct list_head *a, struct list_head *b) struct ubifs_scan_node *sa, *sb; cond_resched(); + if (a == b) + return 0; + sa = list_entry(a, struct ubifs_scan_node, list); sb = list_entry(b, struct ubifs_scan_node, list); @@ -165,6 +168,9 @@ int nondata_nodes_cmp(void *priv, struct list_head *a, struct list_head *b) struct ubifs_scan_node *sa, *sb; cond_resched(); + if (a == b) + return 0; + sa = list_entry(a, struct ubifs_scan_node, list); sb = list_entry(b, struct ubifs_scan_node, list); -- 1.7.1.1 -- Best Regards, Artem Bityutskiy (Артём Битюцкий) -- 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/