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Date: Thu, 2 Dec 2010 09:11:34 -0500
From: Christoph Hellwig <hch@infradead.org>
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Subject: Re: [linux-lvm] Bugs in mkfs.xfs, device mapper, xfs, and /dev/ram
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To: Spelic <spelic@shiftmail.org>
Cc: linux-lvm@redhat.com, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, xfs@oss.sgi.com

I'm pretty sure you have CONFIG_DEBUG_BLOCK_EXT_DEVT enabled.  This
option must never be enabled, as it causes block devices to be
randomly renumered.  Together with the ramdisk driver overloading
the BLKFLSBUF ioctl to discard all data it guarantees you to get
data loss like yours.