linux-kernel - Re: [PATCH block/for-4.5-fixes] writeback: keep superblock pinned during cgroup writeback association switches

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Message-ID: <20160219222609.GC17997@ZenIV.linux.org.uk>
Date:	Fri, 19 Feb 2016 22:26:09 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Tejun Heo <tj@...nel.org>
Cc:	Jan Kara <jack@...e.cz>, Tahsin Erdogan <tahsin@...gle.com>,
	Jens Axboe <axboe@...nel.dk>, cgroups@...r.kernel.org,
	Theodore Ts'o <tytso@....edu>,
	Nauman Rafique <nauman@...gle.com>,
	linux-kernel@...r.kernel.org, Jan Kara <jack@...e.com>
Subject: Re: [PATCH block/for-4.5-fixes] writeback: keep superblock pinned
 during cgroup writeback association switches

On Fri, Feb 19, 2016 at 05:15:12PM -0500, Tejun Heo wrote:

> > IOW, while fs shutdown may be async, making it *always* async would be a bad
> > bug.  And bumping ->s_active does just that.
> > 
> > I'd go for trylock inside that work + making generic_shutdown_super()
> > kill all such works.  I assume that it *can* be abandoned in situation
> > when we know that sync_filesystem() is about to be called and that
> > said sync_filesystem() won't, in turn, schedule any such works, of course...
> 
> I'll make generic_shutdown_super() to kill all such work items.  I
> don't think the work item itself would need further locking tho.  Can
> you please elaborate why you thought adding trylock to the work would
> be necessary?

Umm...  Not much, except that it would make the life cycle rules a bit
more regular.

Is that code OK with e.g. running in parallel with remounting filesystem r/o?