From: Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [Kernel BUG] ext4 for v2.6.32 round II
Date: Wed, 30 Sep 2009 18:57:00 -0700 (PDT)
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Cc: "Theodore Ts'o" <tytso@mit.edu>, linux-ext4@vger.kernel.org,
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To: Markus Trippelsdorf <markus@trippelsdorf.de>
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On Thu, 1 Oct 2009, Markus Trippelsdorf wrote:
> 
> Running latest git I get the following kernel BUG message:
> 
> ------------[ cut here ]------------
> Kernel BUG at ffffffff810efa89 [verbose debug info unavailable]

You really shouldn't turn off verbose debug info unless you are _really_ 
tight on memory in some embedded device. It's not that complex, nor does 
it use a lot of memory, and it makes the error report much harder to 
figure out when the verbose debug output information isn't available.

But in this case I can do it by just looking at the function/offset:

> RIP: 0010:[<ffffffff810efa89>]  [<ffffffff810efa89>] ext4_num_dirty_pages+0x113/0x213

The only BUG_ON() that seems relevant in that function (at least with the 
config I tried with) ends up being

	fs/ext4/inode.c:1184

in my sources, which is from "page_buffers(page)", which has a

	BUG_ON(!PagePrivate(page));

in it. And that would have been much easier to figure out if you had had 
CONFIG_DEBUG_BUGVERBOSE enabled..

Now over to the ext4 people to actually hopefully _solve_ the bug. Maybe 
bisection would help.

		Linus