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From: Duncan <1i5t5.duncan@cox.net>
To: linux-btrfs@vger.kernel.org
Subject: Re: btrfs check segfaults after flipping 2 Bytes
Date: Mon, 6 Oct 2014 04:10:21 +0000 (UTC)	[thread overview]
Message-ID: <pan$37fbc$985496aa$c0a58ffc$edacda92@cox.net> (raw)
In-Reply-To: 5431FEA1.20803@cn.fujitsu.com

Qu Wenruo posted on Mon, 06 Oct 2014 10:29:53 +0800 as excerpted:

> 2 problems here.
> 
> [1] csum mismatch As already mentioned by Ducan and Brendan, the csum
> does not match.
> 
> What makes thing much worse, since small file's extent is inlined, the
> data is stored in metadata tree blocks,
> and the file system is almost empty so the inline extent lies in the
> *root* leaf of fs_tree.
> These two unfortunate facts makes the whole fs_tree corrupted(only one
> leaf, and its cusm dismatch),
> which cause btrfs-progs segfault.

So I nailed it. =:^)

> The good news is that, the bug in btrfs-progs is already fixed by Wang's
> patch:
> https://patchwork.kernel.org/patch/4254631/
> So at least, btrfs-progs will not segfault anymore.
> 
> [2] two occurences?
> So you definitely changed something you should not touch... maybe
> another tree root?

1) Single device btrfs, therefore...
2) DUP metadata by default.

3) Small file, therefore...
4) Inlined in (DUP) metadata, therefore...

5) Two occurrences, each a copy of the (metadata-inlined) file in its own 
instance of the (duped) metadata block.

I nailed it again. =:^)

But the connection between the mentioned tree root patch and this 
particular bug had escaped me, so that's useful new information to me 
too, resolving the problem that I spotted but had no clue whether it was 
even fixable.  Thanks.  =:^)

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman


  reply	other threads:[~2014-10-06  4:10 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-10-01 20:29 btrfs check segfaults after flipping 2 Bytes Niklas Fischer
2014-10-01 20:34 ` Niklas Fischer
2014-10-01 23:31 ` Duncan
2014-10-02  5:51   ` Brendan Hide
2014-10-02 10:58     ` Duncan
2014-10-02 18:38     ` Brendan Hide
2014-10-06  2:29 ` Qu Wenruo
2014-10-06  4:10   ` Duncan [this message]
2014-10-06  4:13     ` Qu Wenruo

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