linux-ext4 - Re: ext4fs error "ext4_mb_generate_buddy:741:group 16, 8160 clusters in bitmap, 4064 in gd" (with repro)

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Date:	Thu, 9 Aug 2012 13:06:40 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Lukas Czerner <lczerner@...hat.com>
Cc:	Paolo Bonzini <pbonzini@...hat.com>,
	"Linux Kernel Mailinlinux-ext4@...r.kernel.orgg List" 
	<linux-kernel@...r.kernel.org>, linux-ext4@...r.kernel.org
Subject: Re: ext4fs error "ext4_mb_generate_buddy:741:group 16, 8160 clusters
 in bitmap, 4064 in gd" (with repro)

On Thu, Aug 09, 2012 at 12:00:09PM +0200, Paolo Bonzini wrote:
> Here is how to reproduce it.  It happens during fstrim.  I found other
> occurrences of the error in the mailing list, but they were not related
> to trim so they may be something different.
> 
> modprobe scsi_debug dev_size_mb=256 lbpws=1
> dd if=/dev/zero of=/dev/sdb bs=1M      
> fdisk /dev/sdb
>  >> create a new partition accepting all defaults
> fdisk -lu /dev/sdb|tail -1
>  >> should show: /dev/sdb1     57      524285      262114+  83  Linux
> 
> mkfs.ext4 /dev/sdb1
> mkdir test
> mount /dev/sdb1 test
> fstrim ./test

I can confirm that this accurately reproduces file system corruption
using a 3.5 kernel.  It looks like some block allocation bitmap blocks
is getting trimmed when it shouldn't have been.  Lukas, can you take a
look at this?

					- Ted
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