linux-kernel - Re: [Kernel BUG] ext4 for v2.6.32 round II

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Date:	Thu, 1 Oct 2009 04:15:31 +0200
From:	Markus Trippelsdorf <markus@...ppelsdorf.de>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Theodore Ts'o <tytso@....edu>, linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [Kernel BUG] ext4 for v2.6.32 round II

On Wed, Sep 30, 2009 at 06:57:00PM -0700, Linus Torvalds wrote:
> 
> 
> 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..
> 

You're right (with CONFIG_DEBUG_BUGVERBOSE=y):

------------[ cut here ]------------
kernel BUG at fs/ext4/inode.c:1184!
...

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

-- 
Markus
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