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

[Mike Snitzer <snitzer@redhat.com>]

On Sat, Mar 21 2015 at 11:11am -0400,
Mike Snitzer <snitzer@redhat.com> wrote:

> On Wed, Jan 14, 2015 at 4:42 AM, Christoph Hellwig <hch@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@lst.de>
> > Reviewed-by: Tejun Heo <tj@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.

FYI, here is the DM fix I've staged for 4.0-rc6.  I'll continue testing
the various DM targets before requesting Linus to pull.