Re: [PATCH 10/10 v7] nfsd: Allows user un-mounting filesystem where nfsd exports base on

From: Al Viro <viro-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org>
To: NeilBrown <neilb-IBi9RG/b67k@public.gmane.org>
Cc: Kinglong Mee
	<kinglongmee-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
	"J. Bruce Fields"
	<bfields-uC3wQj2KruNg9hUCZPvPmw@public.gmane.org>,
	"linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
	<linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	Trond Myklebust
	<trond.myklebust-7I+n7zu2hftEKMMhf/gKZA@public.gmane.org>
Subject: Re: [PATCH 10/10 v7] nfsd: Allows user un-mounting filesystem where nfsd exports base on
Date: Mon, 13 Jul 2015 05:45:53 +0100	[thread overview]
Message-ID: <20150713044553.GN17109@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20150713142059.493a790e@noble>

On Mon, Jul 13, 2015 at 02:20:59PM +1000, NeilBrown wrote:

> Actually, with that change to pin_kill, this side of things becomes
> really easy.
> All expXXX_pin_kill needs to do is call your new cache_delete_entry.
> If that doesn't cause the entry to be put, then something else has a
> temporary reference which will be put soon.  In any case, pin_kill()
> will wait long enough, but not indefinitely.
> No need for kref_get_unless_zero() or any of that.

No.  You are seriously misunderstanding what ->kill() is for and what the
existing instances are doing.  Again, there is no promise whatsoever that
the object containing fs_pin instance will *survive* past ->kill().
At all.

RTFS, please.  What is sorely missing in this recurring patchset is a clear
description of lifetime rules and ordering (who waits for whom and how long).
For all the objects involved.
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