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Re: [PATCH] xfsprogs: libxfs: Don't forget to initialize the radix tree

To: Alex Elder <aelder@xxxxxxx>
Subject: Re: [PATCH] xfsprogs: libxfs: Don't forget to initialize the radix tree subsystem
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Fri, 14 Oct 2011 09:47:44 +1100
Cc: xfs@xxxxxxxxxxx
In-reply-to: <201110131850.p9DIoEvU006578@xxxxxxxxxxxxxxxxxxxxxx>
References: <201110131850.p9DIoEvU006578@xxxxxxxxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Thu, Oct 13, 2011 at 01:50:14PM -0500, Alex Elder wrote:
> The libxfs code uses radix tree routines to manage a mount
> point's m_perag_tree.  But the radix tree routines assume
> that radix_tree_init() has been called to initialize the
> height_to_maxindex[] global array, and this was not being
> done.
> 
> This showed up when running mkfs.xfs on an ia64 system.  Since
> it wasn't initialized, the array was filled with zeroes.  The
> first time radix_tree_extend() got called (with index 0), the
> height would be set to 1 and all would seem fine.
> 
> The *second* time it got called (with index 1) a problem would
> arise--though we were apparently "lucky" enough for it not to
> matter.  The following loop would simply reference invalid slots
> beyond the end of the array until it happened upon one that was
> non-zero.  (I've expanded the function radix_tree_maxindex() here.)
> 
>         /* Figure out what the height should be.  */
>         height = root->height + 1;
>         while (index > height_to_maxindex[height])
>                 height++;
> 
> As an example, this looped 1937 times before it found a non-zere
> value that would cause it to break out of the loop.
> 
> Even that *seemed* to be OK.  But at the end of mkfs.xfs, when
> it calls libxfs_umount(), non-initialized "slots" are dereferenced
> and we hit a fault.
> 
> Wow.
> 
> Signed-off-by: Alex Elder <aelder@xxxxxxx>

/me wonders why valgrind didn't catch that

Anyway, the fix looks good, and well caught!

Reviewed-by: Dave Chinner <dchinner@xxxxxxxxxx>
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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