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Date:   Fri, 6 Dec 2019 16:20:59 -0500
From:   "J. Bruce Fields" <bfields@fieldses.org>
To:     Vasily Averin <vvs@virtuozzo.com>
Cc:     "linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>,
        Chuck Lever <chuck.lever@oracle.com>,
        Trond Myklebust <trond.myklebust@hammerspace.com>,
        Anna Schumaker <anna.schumaker@netapp.com>
Subject: Re: unsafe req->rq_xprt using inside bc_svc_process() ?
Message-ID: <20191206212059.GD17524@fieldses.org>
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 <3b4bd000-13f6-bd4e-a0ea-3e4da3882135@virtuozzo.com>
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On Thu, Dec 05, 2019 at 11:40:04AM +0300, Vasily Averin wrote:
> I've found that Trond fixed it recently in commit 875f0706acc
> "SUNRPC: The TCP back channel mustn't disappear while requests are outstanding"

Thanks for following up!--b.

> 
> On 11/29/19 5:10 PM, Vasily Averin wrote:
> >OpenVz team got complain on crash in bc_svc_process().
> >Crashed node had 15 running containers with active nfsv4.1 mounts,
> >single nfsv4.1-svc thread was processed its back-channel requests.
> >In our case nfs41_callback_svc() took rpc_rqst *req from serv->sv_cb_list
> >started its processing but found that req->rq_xprt points to already freed
> >struct rpc_xprt aka part of struct sock_xprt transport.
> >
> >Back-channel request was submitted via xprt_complete_bc_request(),
> >its processing uses req->rq_xprt reference in many times,
> >however I did not found who keeps this reference.
> >It seems sock_xprt or even whole its net namespace can be freed before bc_svc_process() will start processing of submitted back-channel request, and req->rq_xprt using is unsafe in bc_svc_process()
> >
> >Am I missed something probably?