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Subject: Re: unsafe req->rq_xprt using inside bc_svc_process() ?
From:   Vasily Averin <vvs@virtuozzo.com>
To:     "linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>,
        "J. Bruce Fields" <bfields@fieldses.org>,
        Chuck Lever <chuck.lever@oracle.com>,
        Trond Myklebust <trond.myklebust@hammerspace.com>,
        Anna Schumaker <anna.schumaker@netapp.com>
References: <79494560-1876-494a-0838-cc646eabf68c@virtuozzo.com>
Message-ID: <3b4bd000-13f6-bd4e-a0ea-3e4da3882135@virtuozzo.com>
Date:   Thu, 5 Dec 2019 11:40:04 +0300
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I've found that Trond fixed it recently in commit 875f0706acc
"SUNRPC: The TCP back channel mustn't disappear while requests are outstanding"

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?