Re: [PATCH 1/5] NFSv4: Ensure we reference the inode for return-on-close in delegreturn

From: Trond Myklebust <trond.myklebust@primarydata.com>
To: Peng Tao <tao.peng@primarydata.com>
Cc: Linux NFS Mailing List <linux-nfs@vger.kernel.org>
Subject: Re: [PATCH 1/5] NFSv4: Ensure we reference the inode for return-on-close in delegreturn
Date: Thu, 5 Feb 2015 21:53:09 -0500	[thread overview]
Message-ID: <CAHQdGtQCLpWwV+wdu0-nyrrmemXYgsJWKqiU5yXmmZUYj2RHpg@mail.gmail.com> (raw)
In-Reply-To: <CAKVebiVX7Nd76_byoDgaZfP6ojVZ_WZ_rHu8T+K9TnrCphJ8wA@mail.gmail.com>

On Thu, Feb 5, 2015 at 8:57 PM, Peng Tao <tao.peng@primarydata.com> wrote:
>
> On Fri, Feb 6, 2015 at 9:45 AM, Peng Tao <tao.peng@primarydata.com> wrote:
> > On Fri, Feb 6, 2015 at 6:37 AM, Trond Myklebust
> > <trond.myklebust@primarydata.com> wrote:
> >> If we have to do a return-on-close in the delegreturn code, then
> >> we must ensure that the inode and super block remain referenced.
> >>
> ah, a second thought. I looked for call sites of nfs_sb_active() and
> it gets called at five places in current tree:
> alloc_nfs_open_context, nfs4_opendata_alloc, nfs4_do_close,
> nfs_do_call_unlink, nfs_do_call_unlink
>
> So it appears that sb is activated while any file keeps opened and
> between unlink calls. Then it looks that we are allowed to keep
> delegations after sb is released? Maybe the best way to fix the sb
> reference part is to pin sb when getting the first delegation.

The superblock reference is only there in order to allow us to perform
asynchronous delegreturns without any danger. The problem here is that
we'd end up pinning the superblock even after umount if there are
still unreturned delegations.
That said, I do see that there is a problem with calling
nfs_sb_active() when sb->s_active is zero, so I think I'd like to fix
that up.

-- 
Trond Myklebust
Linux NFS client maintainer, PrimaryData
trond.myklebust@primarydata.com