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From:   NeilBrown <neilb@suse.de>
To:     Trond Myklebust <trondmy@gmail.com>, linux-nfs@vger.kernel.org
Date:   Thu, 17 Oct 2019 09:24:53 +1100
Cc:     Chuck Lever <chuck.lever@oracle.com>,
        Anna Schumaker <Anna.Schumaker@netapp.com>,
        "J. Bruce Fields" <bfields@redhat.com>
Subject: Re: [PATCH 1/3] SUNRPC: The TCP back channel mustn't disappear while requests are outstanding
In-Reply-To: <20191016141546.32277-1-trond.myklebust@hammerspace.com>
References: <20191016141546.32277-1-trond.myklebust@hammerspace.com>
Message-ID: <87pniwpbuy.fsf@notabene.neil.brown.name>
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On Wed, Oct 16 2019, Trond Myklebust wrote:

> If there are TCP back channel requests either being processed by the
> server threads, then we should hold a reference to the transport
> to ensure it doesn't get freed from underneath us.
>
> Reported-by: Neil Brown <neilb@suse.de>
> Fixes: 2ea24497a1b3 ("SUNRPC: RPC callbacks may be split across several..=
")
> Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
> ---
>  net/sunrpc/backchannel_rqst.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/net/sunrpc/backchannel_rqst.c b/net/sunrpc/backchannel_rqst.c
> index 339e8c077c2d..7eb251372f94 100644
> --- a/net/sunrpc/backchannel_rqst.c
> +++ b/net/sunrpc/backchannel_rqst.c
> @@ -307,8 +307,8 @@ void xprt_free_bc_rqst(struct rpc_rqst *req)
>  		 */
>  		dprintk("RPC:       Last session removed req=3D%p\n", req);
>  		xprt_free_allocation(req);
> -		return;
>  	}
> +	xprt_put(xprt);
>  }
>=20=20
>  /*
> @@ -339,7 +339,7 @@ struct rpc_rqst *xprt_lookup_bc_request(struct rpc_xp=
rt *xprt, __be32 xid)
>  		spin_unlock(&xprt->bc_pa_lock);
>  		if (new) {
>  			if (req !=3D new)
> -				xprt_free_bc_rqst(new);
> +				xprt_free_allocation(new);
>  			break;
>  		} else if (req)
>  			break;
> @@ -368,6 +368,7 @@ void xprt_complete_bc_request(struct rpc_rqst *req, u=
int32_t copied)
>  	set_bit(RPC_BC_PA_IN_USE, &req->rq_bc_pa_state);
>=20=20
>  	dprintk("RPC:       add callback request to list\n");
> +	xprt_get(xprt);
>  	spin_lock(&bc_serv->sv_cb_lock);
>  	list_add(&req->rq_bc_list, &bc_serv->sv_cb_list);
>  	wake_up(&bc_serv->sv_cb_waitq);
> --=20
> 2.21.0

Looks good.
This and the next two:
 Reviewed-by: NeilBrown <neilb@suse.de>

It would help me if you could add a Fixes: tag to at least the first
two.

BTW, while reviewing I notices that bc_alloc_count and bc_slot_count are
almost identical.  The three places were that are changed separately are
probably (minor) bugs.
Do you recall why there were two different counters?  Has the reason
disappeared?

Thanks,
NeilBrown

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