Re: [PATCH stable] block: discard bdi_unregister() in favour of bdi_destroy()

From: Peter Zijlstra
Date: Thu Apr 30 2015 - 04:36:09 EST

On Thu, Apr 30, 2015 at 10:32:33AM +1000, NeilBrown wrote:
> bdi_unregister() now contains very little functionality.
> It contains a "WARN_ON" if bdi->dev is NULL. This warning is of no
> real consequence as bdi->dev isn't needed by anything else in the function,
> and it triggers if
> blk_cleanup_queue() -> bdi_destroy()
> is called before bdi_unregister, which a subsequent patch will make happen.
> So this isn't wanted.
> It also calls bdi_set_min_ratio(). This needs to be called after
> writes through the bdi have all been flushed, and before the bdi is destroyed.
> Calling it early is better than calling it late as it frees up a global
> resource.
> Calling it immediately after bdi_wb_shutdown() in bdi_destroy()
> perfectly fits these requirements.
> So bdi_unregister can be discarded with the important content moved to
> bdi_destroy, as can the
> writeback_bdi_unregister
> event which is already not used.
> This is tagged for 'stable' as it is a pre-requisite for a subsequent
> patch which moves calls to blk_cleanup_queue() before calls to
> del_gendisk(). The commit identified as 'Fixes' removed a lot of
> other functionality from bdi_unregister(), and made a change which
> necessitated moving the blk_cleanup_queue() calls.
> Reported-by: Mike Snitzer <snitzer@xxxxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx (v4.0)
> Fixes: c4db59d31e39ea067c32163ac961e9c80198fd37

Fixes: c4db59d31e39 ("fs: don't reassign dirty inodes to default_backing_dev_info")

> Signed-off-by: NeilBrown <neilb@xxxxxxx>

Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
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