linux-kernel - Re: [PATCH v2 7/8] shift percpu_counter_destroy() into destroy_super

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Message-ID: <20150813133616.GC15609@redhat.com>
Date:	Thu, 13 Aug 2015 15:36:16 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Jan Kara <jack@...e.cz>
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	Dave Chinner <david@...morbit.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 7/8] shift percpu_counter_destroy() into
	destroy_super_work()

On 08/13, Jan Kara wrote:
>
> On Tue 11-08-15 19:04:16, Oleg Nesterov wrote:
> >
> > So this is just the temporary kludge which helps us to avoid the
> > conflicts with the changes which will be (hopefully) routed via
> > rcu tree.
> >
> > Signed-off-by: Oleg Nesterov <oleg@...hat.com>
>
> Looking into this again, it would seem somewhat cleaner to me to move the
> destruction to deactivate_locked_super() instead.

Heh ;) You know, I was looking at deactivate_locked_super(). However, I
simply do not understand this code enough, I failed to verify it would
be safe to destroy s_writers there.

And. Please note destroy_super() in alloc_super() error path, so this
needs a bit more changes in any case.

Can't we live with this hack for now? To remind, it will be reverted
(at least partially) in any case. Yes, yes, it is very ugly and the
changelog documents this fact. But it looks simple and safe. To me
it would be better to make the conversion first, then cleanup this
horror after another discussion.

What do you think?

Oleg.

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