SUNRPC: Per-rpc_clnt task PIDs

The current range of RPC task PIDs is 0..65535. That's not adequate
for distinguishing tasks across multiple rpc_clnts running high
throughput workloads.

To help relieve this situation and to reduce the bottleneck of
having a single atomic for assigning all RPC task PIDs, assign task
PIDs per rpc_clnt.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

include/linux/sunrpc/clnt.h

@@ -40,6 +40,7 @@ struct rpc_clnt {
 	unsigned int		cl_clid;	/* client id */
 	struct list_head	cl_clients;	/* Global list of clients */
 	struct list_head	cl_tasks;	/* List of tasks */
+	atomic_t		cl_pid;		/* task PID counter */
 	spinlock_t		cl_lock;	/* spinlock */
 	struct rpc_xprt __rcu *	cl_xprt;	/* transport */
 	const struct rpc_procinfo *cl_procinfo;	/* procedure info */

net/sunrpc/sched.c

@@ -277,9 +277,17 @@ static int rpc_wait_bit_killable(struct wait_bit_key *key, int mode)
 #if IS_ENABLED(CONFIG_SUNRPC_DEBUG) || IS_ENABLED(CONFIG_TRACEPOINTS)
 static void rpc_task_set_debuginfo(struct rpc_task *task)
 {
-	static atomic_t rpc_pid;
+	struct rpc_clnt *clnt = task->tk_client;
 
-	task->tk_pid = atomic_inc_return(&rpc_pid);
+	/* Might be a task carrying a reverse-direction operation */
+	if (!clnt) {
+		static atomic_t rpc_pid;
+
+		task->tk_pid = atomic_inc_return(&rpc_pid);
+		return;
+	}
+
+	task->tk_pid = atomic_inc_return(&clnt->cl_pid);
 }
 #else
 static inline void rpc_task_set_debuginfo(struct rpc_task *task)