linux-kernel - Re: [PATCH stable] block: discard bdi_unregister() in favour of bdi

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Date:	Thu, 30 Apr 2015 10:35:03 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	NeilBrown <neilb@...e.de>
Cc:	Jens Axboe <axboe@...com>, Christoph Hellwig <hch@....de>,
	Mike Snitzer <snitzer@...hat.com>,
	Azat Khuzhin <a3at.mail@...il.com>,
	"Kernel.org-Linux-RAID" <linux-raid@...r.kernel.org>,
	Guoqing Jiang <GQJiang@...e.com>, Tejun Heo <tj@...nel.org>,
	Jan Kara <jack@...e.cz>, lkml <linux-kernel@...r.kernel.org>,
	device-mapper development <dm-devel@...hat.com>
Subject: Re: [PATCH stable] block: discard bdi_unregister() in favour of
 bdi_destroy()

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@...hat.com>
> Cc: Christoph Hellwig <hch@....de>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: stable@...r.kernel.org (v4.0)
> Fixes: c4db59d31e39ea067c32163ac961e9c80198fd37

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

> Signed-off-by: NeilBrown <neilb@...e.de>

Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
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