From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH 2/9] writeback: switch to per-bdi threads for flushing
	data
Date: Thu, 6 Aug 2009 17:44:33 -0400
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Cc: Jens Axboe <jens.axboe@oracle.com>, linux-kernel@vger.kernel.org,
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To: Jan Kara <jack@suse.cz>
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On Wed, Aug 05, 2009 at 06:35:32PM +0200, Jan Kara wrote:
>   Jens, sorry about bitching about this again but you're silently changing
> substantial locking assumptions without writing it *anywhere* and without
> arguing it's safe.
>   Originally, generic_sync_sb_inodes() from writeback path have been
> called with
> a) s_umount_sem held
> b) sb->s_count elevated
>   The second still seems to be true since, if I'm right, we pass here
> non-NULL sb only from sync_filesystem() and that takes care of the
> superblock reference. So that is just a matter of documenting this fact
> before the function.

We'll defintively need to keep both to prevent races vs unmount.  And
with a NULL superblock passed I'm not even sure how we can take care of
it.