linux-kernel - Re: [PATCH -next] SUNRPC: Clean XPRT_CONGESTED of xprt->state when rpc task is killed

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Date:   Mon, 20 Dec 2021 18:22:27 +0000
From:   Trond Myklebust <trondmy@...merspace.com>
To:     "cuibixuan@...ux.alibaba.com" <cuibixuan@...ux.alibaba.com>,
        "linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     "anna.schumaker@...app.com" <anna.schumaker@...app.com>,
        "xiaoh.peixh@...baba-inc.com" <xiaoh.peixh@...baba-inc.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "chuck.lever@...cle.com" <chuck.lever@...cle.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "bfields@...ldses.org" <bfields@...ldses.org>,
        "wenan.mwa@...baba-inc.com" <wenan.mwa@...baba-inc.com>,
        "weipu.zy@...baba-inc.com" <weipu.zy@...baba-inc.com>,
        "pete.wl@...baba-inc.com" <pete.wl@...baba-inc.com>
Subject: Re: [PATCH -next] SUNRPC: Clean XPRT_CONGESTED of xprt->state when
 rpc task is killed

On Mon, 2021-12-20 at 11:39 +0800, Bixuan Cui wrote:
> ping~
> 
> 在 2021/12/14 下午9:53, Bixuan Cui 写道:
> > When the values of tcp_max_slot_table_entries and
> > sunrpc.tcp_slot_table_entries are lower than the number of rpc
> > tasks,
> > xprt_dynamic_alloc_slot() in xprt_alloc_slot() will return -EAGAIN,
> > and
> > then set xprt->state to XPRT_CONGESTED:
> >    xprt_retry_reserve
> >      ->xprt_do_reserve
> >        ->xprt_alloc_slot
> >          ->xprt_dynamic_alloc_slot // return -EAGAIN and task-
> > >tk_rqstp is NULL
> >            ->xprt_add_backlog // set_bit(XPRT_CONGESTED, &xprt-
> > >state);
> > 
> > When rpc task is killed, XPRT_CONGESTED bit of xprt->state will not
> > be
> > cleaned up and nfs hangs:
> >    rpc_exit_task
> >      ->xprt_release // if (req == NULL) is true, then
> > XPRT_CONGESTED
> >                    // bit not clean
> > 
> > Add xprt_wake_up_backlog(xprt) to clean XPRT_CONGESTED bit in
> > xprt_release().

I'm not seeing how this explanation makes sense. If the task doesn't
hold a slot, then freeing that task isn't going to clear the congestion
caused by all the slots being in use.


-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@...merspace.com