Messages in this thread Patch in this message |  | | | Subject | Re: [PATCH 0/6] improve list_sort test | | From | Artem Bityutskiy <> | | Date | Sun, 08 Aug 2010 13:03:09 +0300 |
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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 <Artem.Bityutskiy@nokia.com> 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 <don.mullis@gmail.com> 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 <Artem.Bityutskiy@nokia.com> --- 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)
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