[PATCH 11/12] fs: don't reassign dirty inodes to default_backing_dev_info

[Mike Snitzer]

On Wed, Jan 14, 2015 at 4:42 AM, Christoph Hellwig <hch at lst.de> wrote:
> If we have dirty inodes we need to call the filesystem for it, even if the
> device has been removed and the filesystem will error out early.  The
> current code does that by reassining all dirty inodes to the default
> backing_dev_info when a bdi is unlinked, but that's pretty pointless given
> that the bdi must always outlive the super block.
>
> Instead of stopping writeback at unregister time and moving inodes to the
> default bdi just keep the current bdi alive until it is destroyed.  The
> containing objects of the bdi ensure this doesn't happen until all
> writeback has finished by erroring out.
>
> Signed-off-by: Christoph Hellwig <hch at lst.de>
> Reviewed-by: Tejun Heo <tj at kernel.org>
> ---
>  mm/backing-dev.c | 91 +++++++++++++++-----------------------------------------
>  1 file changed, 24 insertions(+), 67 deletions(-)

Hey Christoph,

Just a heads up: your commit c4db59d31e39ea067c32163ac961e9c80198fd37
is suspected as the first bad commit in a bisect performed to track
down the cause of DM crashes reported in this BZ:
https://bugzilla.redhat.com/show_bug.cgi?id=1202449

I've yet to look closely at _why_ this commit but figured I'd share
since this appears to be a 4.0-rcX regression.

Mike