smb3: display max smb3 requests in flight at any one time

Displayed in /proc/fs/cifs/Stats once for each
socket we are connected to.

This allows us to find out what the maximum number of
requests that had been in flight (at any one time). Note that
/proc/fs/cifs/Stats can be reset if you want to look for
maximum over a small period of time.

Sample output (immediately after mount):

Resources in use
CIFS Session: 1
Share (unique mount targets): 2
SMB Request/Response Buffer: 1 Pool size: 5
SMB Small Req/Resp Buffer: 1 Pool size: 30
Operations (MIDs): 0

0 session 0 share reconnects
Total vfs operations: 5 maximum at one time: 2

Max requests in flight: 2
1) \\localhost\scratch
SMBs: 18
Bytes read: 0 Bytes written: 0
...

Signed-off-by: Steve French <[e-mail]>
Reviewed-by: Pavel Shilovsky <[e-mail]>

fs/cifs/cifs_debug.c

···
 		list_for_each(tmp1, &cifs_tcp_ses_list) {
 			server = list_entry(tmp1, struct TCP_Server_Info,
 					    tcp_ses_list);
+			server->max_in_flight = 0;
 #ifdef CONFIG_CIFS_STATS2
 			for (i = 0; i < NUMBER_OF_SMB2_COMMANDS; i++) {
 				atomic_set(&server->num_cmds[i], 0);
···
 	list_for_each(tmp1, &cifs_tcp_ses_list) {
 		server = list_entry(tmp1, struct TCP_Server_Info,
 				    tcp_ses_list);
+		seq_printf(m, "\nMax requests in flight: %d", server->max_in_flight);
 #ifdef CONFIG_CIFS_STATS2
 		seq_puts(m, "\nTotal time spent processing by command. Time ");
 		seq_printf(m, "units are jiffies (%d per second)\n", HZ);

fs/cifs/cifsglob.h

···
 	unsigned int credits;  /* send no more requests at once */
 	unsigned int max_credits; /* can override large 32000 default at mnt */
 	unsigned int in_flight;  /* number of requests on the wire to server */
+	unsigned int max_in_flight; /* max number of requests that were on wire */
 	spinlock_t req_lock;  /* protect the two values above */
 	struct mutex srv_mutex;
 	struct task_struct *tsk;

fs/cifs/connect.c

···
 	tcp_ses->tcp_nodelay = volume_info->sockopt_tcp_nodelay;
 	tcp_ses->rdma = volume_info->rdma;
 	tcp_ses->in_flight = 0;
+	tcp_ses->max_in_flight = 0;
 	tcp_ses->credits = 1;
 	init_waitqueue_head(&tcp_ses->response_q);
 	init_waitqueue_head(&tcp_ses->request_q);

fs/cifs/smb2ops.c

···
 			credits->instance = server->reconnect_instance;
 			server->credits -= credits->value;
 			server->in_flight++;
+			if (server->in_flight > server->max_in_flight)
+				server->max_in_flight = server->in_flight;
 			break;
 		}
 	}

fs/cifs/transport.c

···
 	if ((flags & CIFS_TIMEOUT_MASK) == CIFS_NON_BLOCKING) {
 		/* oplock breaks must not be held up */
 		server->in_flight++;
+		if (server->in_flight > server->max_in_flight)
+			server->max_in_flight = server->in_flight;
 		*credits -= 1;
 		*instance = server->reconnect_instance;
 		spin_unlock(&server->req_lock);
···
 			if ((flags & CIFS_TIMEOUT_MASK) != CIFS_BLOCKING_OP) {
 				*credits -= num_credits;
 				server->in_flight += num_credits;
+				if (server->in_flight > server->max_in_flight)
+					server->max_in_flight = server->in_flight;
 				*instance = server->reconnect_instance;
 			}
 			spin_unlock(&server->req_lock);