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Date:   Fri, 25 Oct 2019 11:33:36 -0400
To:     "J. Bruce Fields" <bfields@redhat.com>
Cc:     Trond Myklebust <trondmy@hammerspace.com>,
        "linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>
Subject: Re: [PATCH v2] nfsd: Fix races between nfsd4_cb_release() and
 nfsd4_shutdown_callback()
Message-ID: <20191025153336.GA20283@fieldses.org>
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From:   bfields@fieldses.org (J. Bruce Fields)
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On Fri, Oct 25, 2019 at 11:21:19AM -0400, J. Bruce Fields wrote:
> On Fri, Oct 25, 2019 at 02:55:45PM +0000, Trond Myklebust wrote:
> > On Fri, 2019-10-25 at 10:51 -0400, J. Bruce Fields wrote:
> > > On Wed, Oct 23, 2019 at 05:43:18PM -0400, Trond Myklebust wrote:
> > > > When we're destroying the client lease, and we call
> > > > nfsd4_shutdown_callback(), we must ensure that we do not return
> > > > before all outstanding callbacks have terminated and have
> > > > released their payloads.
> > > 
> > > This is great, thanks!  We've seen what I'm fairly sure is the same
> > > bug
> > > from Red Hat users.  I think my blind spot was an assumption that
> > > rpc tasks wouldn't outlive rpc_shutdown_client().
> > > 
> > > However, it's causing xfstests runs to hang, and I haven't worked out
> > > why yet.
> > > 
> > > I'll spend some time on it this afternoon and let you know what I
> > > figure
> > > out.
> > > 
> > 
> > Is that happening with v2 or with v1? With v1 there is definitely a
> > hang in __destroy_client() due to the refcount leak that I believe I
> > fixed in v2.
> 
> I thought I was running v2, let me double-check....

Yes, with v2 I'm getting a hang on generic/013.

I checked quickly and didn't see anything interesting in the logs,
otherwise I haven't done any digging.

--b.