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Date:   Sun, 22 May 2022 20:36:48 +0800
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Subject: [PATCH v2] xprtrdma: treat all calls not a bcall when bc_serv is NULL
Content-Language: en-US
To:     Chuck Lever III <chuck.lever@oracle.com>,
        Anna Schumaker <anna@kernel.org>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>
References: <3d65c9a2-6c3e-7224-5701-c3e0060b6df6@gmail.com>
 <FE1A00F7-3CAF-4B62-9DD6-0EADF44D3059@oracle.com>
 <09f0b58c-37d7-4b8d-0285-01ec11601d01@gmail.com>
 <9F4E9614-9891-4787-86DC-944BEB45C960@oracle.com>
From:   Kinglong Mee <kinglongmee@gmail.com>
In-Reply-To: <9F4E9614-9891-4787-86DC-944BEB45C960@oracle.com>
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When a rdma server returns a fault format reply, nfs v3 client may
treats it as a bcall when bc service is not exist.

The debug message at rpcrdma_bc_receive_call are,

[56579.837169] RPC:       rpcrdma_bc_receive_call: callback XID 
00000001, length=20
[56579.837174] RPC:       rpcrdma_bc_receive_call: 00 00 00 01 00 00 00 
00 00 00 00 00 00 00 00 00 00 00 00 04

After that, 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..190a4de239c8 100644
--- a/net/sunrpc/xprtrdma/rpc_rdma.c
+++ b/net/sunrpc/xprtrdma/rpc_rdma.c
@@ -1121,6 +1121,7 @@ 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;

@@ -1144,6 +1145,10 @@ rpcrdma_is_bcall(struct rpcrdma_xprt *r_xprt, 
struct rpcrdma_rep *rep)
  	if (*p != cpu_to_be32(RPC_CALL))
  		return false;

+	/* No bc service. */
+	if (xprt->bc_serv == NULL)
+		return false;
+
  	/* Now that we are sure this is a backchannel call,
  	 * advance to the RPC header.
  	 */
-- 
2.27.0