linux-ext4 - Re: Commit c1a1e7fc24d6 causes segfault in ext2fs_new

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Date:	Wed, 04 Apr 2012 20:56:02 -0700
From:	Eric Sandeen <sandeen@...hat.com>
To:	"Richard W.M. Jones" <rjones@...hat.com>
CC:	Ext4 Developers List <linux-ext4@...r.kernel.org>,
	Sami Liedes <sami.liedes@....fi>
Subject: Re: Commit c1a1e7fc24d6 causes segfault in ext2fs_new_inode

On 3/30/12 5:57 AM, Richard W.M. Jones wrote:
> [I'm tracking this issue here:
> https://bugzilla.redhat.com/show_bug.cgi?id=808421]
> 
> febootstrap uses the ext2fs library to construct an ext2 filesystem.
> 
> Since we updated to the latest version in git, febootstrap segfaults
> in ext2fs_find_first_zero_generic_bmap (called from ext2fs_new_inode).
> There's a complete stack trace in the bug above.
> 
> I'm not claiming that we are calling this library correctly, but,
> you know, "it always worked until now".

Sami, can you take a look at this one?  It seems that your commit does
not handle 32-bit bitmaps.

Thanks,
-Eric

> Here is the calling code:
> 
> https://github.com/libguestfs/febootstrap/blob/636a80b5a70382f21da47c44a0acd3efa2bc7fcf/helper/ext2.c#L142
> 
> git bisect points to this change being the one which causes the
> problem:
> 
> c1a1e7fc24d6e37f931bbb8eeb29c90243f0a55d is the first bad commit
> commit c1a1e7fc24d6e37f931bbb8eeb29c90243f0a55d
> Author: Sami Liedes <sami.liedes@....fi>
> Date:   Sat Mar 10 22:36:12 2012 +0200
> 
>     libext2fs: Implement ext2fs_find_first_zero_generic_bmap().
>     
>     This function searches a bitmap for the first zero bit within a range.
>     It checks if there is a bitmap backend specific implementation
>     available (if the relevant field in bitmap_ops is non-NULL). If not,
>     it uses a generic and slow method by repeatedly calling test_bmap() in
>     a loop. Also change ext2fs_new_inode() to use this new function.
>     
>     This change in itself does not result in a large speedup, rather it
>     refactors the code in preparation for the introduction of a faster
>     find_first_zero() for bitarray based bitmaps.
>     
>     Signed-off-by: Sami Liedes <sami.liedes@....fi>
>     Signed-off-by: Theodore Ts'o <tytso@....edu>
> 
> Rich.
> 

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