linux-kernel - Re: [PATCH 10/16] writeback: splice dirty inode entries to default bdi on bdi

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Message-ID: <20090916182932.GR23126@kernel.dk>
Date:	Wed, 16 Sep 2009 20:29:32 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Jan Kara <jack@...e.cz>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	chris.mason@...cle.com, hch@...radead.org, tytso@....edu,
	akpm@...ux-foundation.org, trond.myklebust@....uio.no
Subject: Re: [PATCH 10/16] writeback: splice dirty inode entries to default
	bdi on bdi_destroy()

On Wed, Sep 16 2009, Jan Kara wrote:
> On Wed 16-09-09 15:24:48, Jens Axboe wrote:
> > We cannot safely ensure that the inodes are all gone at this point
> > in time, and we must not destroy this bdi with inodes having off it.
> > So just splice our entries to the default bdi since that one will
> > always persist.
>   I'd at least add a comment like
> "XXX: This is probably a bug but let's workaround it for now."
>   And either remove the code or update the comment when this gets resolved.

Thinking more about it - what if inodes happen to get requeued on the
final flush? bdi_destroy() likely can't wait for flushing to happen,
since (depending on the tear down cycle), part of the device may be gone
already.

And I did mean __sync_filesystem() -> __sync_blockdev(), since this is
what happen on last close. So it could also be that we need something
stronger to guarantee that things are really gone.

-- 
Jens Axboe

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