From: Dave Chinner <david@fromorbit.com>
Subject: Re: [PATCH 2/2] generic: test I/O on dm error device
Date: Tue, 15 Mar 2016 13:46:16 +1100
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To: Eryu Guan <eguan@redhat.com>
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On Fri, Mar 11, 2016 at 11:40:22PM +0800, Eryu Guan wrote:
> This is a test that performs simple I/O on dm error device, which
> returns EIO on all I/O request.
> 
> This is motivated by an ext4 bug that crashes kernel on error path when
> trying to update atime. Following kernel patch should fix the issue
> 
>   ext4: fix NULL pointer dereference in ext4_mark_inode_dirty()

Why does this test require the loop device? Why can't you just
unmount the filesystem, run 'blkdev --flushbufs <dev>' to ensure
there are no cached buffers/pages on the block device, then mount
it again?

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com