Re: [PATCH] xprtrdam: Don't treat a call as bcall when bc_serv is NULL

From: Chuck Lever III <chuck.lever@oracle.com>
To: Kinglong Mee <kinglongmee@gmail.com>
Cc: Anna Schumaker <anna@kernel.org>,
	Linux NFS Mailing List <linux-nfs@vger.kernel.org>
Subject: Re: [PATCH] xprtrdam: Don't treat a call as bcall when bc_serv is NULL
Date: Sat, 21 May 2022 16:33:54 +0000	[thread overview]
Message-ID: <FE1A00F7-3CAF-4B62-9DD6-0EADF44D3059@oracle.com> (raw)
In-Reply-To: <3d65c9a2-6c3e-7224-5701-c3e0060b6df6@gmail.com>

> On May 21, 2022, at 5:51 AM, Kinglong Mee <kinglongmee@gmail.com> wrote:
> 
> When rdma server returns a fault reply, rpcrdma may treats it as a bcall.
> As using NFSv3, a bc server is never exist.
> rpcrdma_bc_receive_call will meets NULL pointer as,
> 
> [  226.057890] BUG: unable to handle kernel NULL pointer dereference at 00000000000000c8
> ...
> [  226.058704] RIP: 0010:_raw_spin_lock+0xc/0x20
> ...
> [  226.059732] Call Trace:
> [  226.059878]  rpcrdma_bc_receive_call+0x138/0x327 [rpcrdma]
> [  226.060011]  __ib_process_cq+0x89/0x170 [ib_core]
> [  226.060092]  ib_cq_poll_work+0x26/0x80 [ib_core]
> [  226.060257]  process_one_work+0x1a7/0x360
> [  226.060367]  ? create_worker+0x1a0/0x1a0
> [  226.060440]  worker_thread+0x30/0x390
> [  226.060500]  ? create_worker+0x1a0/0x1a0
> [  226.060574]  kthread+0x116/0x130
> [  226.060661]  ? kthread_flush_work_fn+0x10/0x10
> [  226.060724]  ret_from_fork+0x35/0x40
> ...
> 
> Signed-off-by: Kinglong Mee <kinglongmee@gmail.com>
> ---
> net/sunrpc/xprtrdma/rpc_rdma.c | 5 +++++
> 1 file changed, 5 insertions(+)
> 
> diff --git a/net/sunrpc/xprtrdma/rpc_rdma.c b/net/sunrpc/xprtrdma/rpc_rdma.c
> index 281ddb87ac8d..9486bb98eb2f 100644
> --- a/net/sunrpc/xprtrdma/rpc_rdma.c
> +++ b/net/sunrpc/xprtrdma/rpc_rdma.c
> @@ -1121,9 +1121,14 @@ static bool
> rpcrdma_is_bcall(struct rpcrdma_xprt *r_xprt, struct rpcrdma_rep *rep)
> #if defined(CONFIG_SUNRPC_BACKCHANNEL)
> {
> +	struct rpc_xprt *xprt = &r_xprt->rx_xprt;
> 	struct xdr_stream *xdr = &rep->rr_stream;
> 	__be32 *p;
> 
> +	/* no bc service, not a bcall. */
> +	if (xprt->bc_serv == NULL)
> +		return false;
> +
> 	if (rep->rr_proc != rdma_msg)
> 		return false;

I'm not sure what you mean above by "fault reply".

The check here for whether the RPC/RDMA procedure is an RDMA_MSG
is supposed to be enough to avoid any further processing of an
RDMA_ERR type procedure.

What kind of fault has occurred? Can you share with us the
actual RPC/RDMA transport header that triggers the BUG?

--
Chuck Lever