svcrdma: Hold private mutex while invoking rdma_accept()

stable inclusion
from stable-5.10.20
commit 426b8fb3d6724469937fb3d256397bdcf37d705d
bugzilla: 50608

--------------------------------

[ Upstream commit 0ac24c32 ]

RDMA core mutex locking was restructured by commit d114c6fe
("RDMA/cma: Add missing locking to rdma_accept()") [Aug 2020]. When
lock debugging is enabled, the RPC/RDMA server trips over the new
lockdep assertion in rdma_accept() because it doesn't call
rdma_accept() from its CM event handler.

As a temporary fix, have svc_rdma_accept() take the handler_mutex
explicitly. In the meantime, let's consider how to restructure the
RPC/RDMA transport to invoke rdma_accept() from the proper context.

Calls to svc_rdma_accept() are serialized with calls to
svc_rdma_free() by the generic RPC server layer.
Suggested-by: NJason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/linux-rdma/20210209154014.GO4247@nvidia.com/
Fixes: d114c6fe ("RDMA/cma: Add missing locking to rdma_accept()")
Signed-off-by: NChuck Lever <chuck.lever@oracle.com>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Acked-by: NXie XiuQi <xiexiuqi@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

net/sunrpc/xprtrdma/svc_rdma_transport.c

@@ -475,9 +475,6 @@ static struct svc_xprt *svc_rdma_accept(struct svc_xprt *xprt)
 	if (!svc_rdma_post_recvs(newxprt))
 		goto errout;
 
-	/* Swap out the handler */
-	newxprt->sc_cm_id->event_handler = svc_rdma_cma_handler;
-
 	/* Construct RDMA-CM private message */
 	pmsg.cp_magic = rpcrdma_cmp_magic;
 	pmsg.cp_version = RPCRDMA_CMP_VERSION;
@@ -498,7 +495,10 @@ static struct svc_xprt *svc_rdma_accept(struct svc_xprt *xprt)
 	}
 	conn_param.private_data = &pmsg;
 	conn_param.private_data_len = sizeof(pmsg);
+	rdma_lock_handler(newxprt->sc_cm_id);
+	newxprt->sc_cm_id->event_handler = svc_rdma_cma_handler;
 	ret = rdma_accept(newxprt->sc_cm_id, &conn_param);
+	rdma_unlock_handler(newxprt->sc_cm_id);
 	if (ret) {
 		trace_svcrdma_accept_err(newxprt, ret);
 		goto errout;