smb: client: add mid_counter_lock to protect the mid counter counter

This is step 2/4 of a patch series to fix mid_q_entry memory leaks
caused by race conditions in callback execution.

Add a dedicated mid_counter_lock to protect current_mid counter,
separating it from mid_queue_lock which protects pending_mid_q
operations. This reduces lock contention and prepares for finer-
grained locking in subsequent patches.

Changes:
- Add TCP_Server_Info->mid_counter_lock spinlock
- Rename CurrentMid to current_mid for consistency
- Use mid_counter_lock to protect current_mid access
- Update locking documentation in cifsglob.h

This separation allows mid allocation to proceed without blocking
queue operations, improving performance under heavy load.

Signed-off-by: Wang Zhaolong <[email protected]>
Acked-by: Enzo Matsumiya <[email protected]>
Signed-off-by: Steve French <[email protected]>

Author: Wang Zhaolong

fs/smb/client/cifsglob.h

@@ -733,6 +733,7 @@ struct TCP_Server_Info {
 	wait_queue_head_t response_q;
 	wait_queue_head_t request_q; /* if more than maxmpx to srvr must block*/
 	spinlock_t mid_queue_lock;  /* protect mid queue */
+	spinlock_t mid_counter_lock;
 	struct list_head pending_mid_q;
 	bool noblocksnd;		/* use blocking sendmsg */
 	bool noautotune;		/* do not autotune send buf sizes */
@@ -770,7 +771,7 @@ struct TCP_Server_Info {
 	/* SMB_COM_WRITE_RAW or SMB_COM_READ_RAW. */
 	unsigned int capabilities; /* selective disabling of caps by smb sess */
 	int timeAdj;  /* Adjust for difference in server time zone in sec */
-	__u64 CurrentMid;         /* multiplex id - rotating counter, protected by GlobalMid_Lock */
+	__u64 current_mid;	/* multiplex id - rotating counter, protected by mid_counter_lock */
 	char cryptkey[CIFS_CRYPTO_KEY_SIZE]; /* used by ntlm, ntlmv2 etc */
 	/* 16th byte of RFC1001 workstation name is always null */
 	char workstation_RFC1001_name[RFC1001_NAME_LEN_WITH_NULL];
@@ -2008,8 +2009,8 @@ require use of the stronger protocol */
  *				GlobalTotalActiveXid
  * TCP_Server_Info->srv_lock	(anything in struct not protected by another lock and can change)
  * TCP_Server_Info->mid_queue_lock	TCP_Server_Info->pending_mid_q	cifs_get_tcp_session
- *				->CurrentMid
  *				(any changes in mid_q_entry fields)
+ * TCP_Server_Info->mid_counter_lock    TCP_Server_Info->current_mid    cifs_get_tcp_session
  * TCP_Server_Info->req_lock	TCP_Server_Info->in_flight	cifs_get_tcp_session
  *				->credits
  *				->echo_credits

fs/smb/client/connect.c

@@ -358,7 +358,7 @@ static bool cifs_tcp_ses_needs_reconnect(struct TCP_Server_Info *server, int num
 	}
 
 	cifs_dbg(FYI, "Mark tcp session as need reconnect\n");
-	trace_smb3_reconnect(server->CurrentMid, server->conn_id,
+	trace_smb3_reconnect(server->current_mid, server->conn_id,
 			     server->hostname);
 	server->tcpStatus = CifsNeedReconnect;
 
@@ -1242,7 +1242,7 @@ smb2_add_credits_from_hdr(char *buffer, struct TCP_Server_Info *server)
 		spin_unlock(&server->req_lock);
 		wake_up(&server->request_q);
 
-		trace_smb3_hdr_credits(server->CurrentMid,
+		trace_smb3_hdr_credits(server->current_mid,
 				server->conn_id, server->hostname, scredits,
 				le16_to_cpu(shdr->CreditRequest), in_flight);
 		cifs_server_dbg(FYI, "%s: added %u credits total=%d\n",
@@ -1823,6 +1823,7 @@ cifs_get_tcp_session(struct smb3_fs_context *ctx,
 	spin_lock_init(&tcp_ses->req_lock);
 	spin_lock_init(&tcp_ses->srv_lock);
 	spin_lock_init(&tcp_ses->mid_queue_lock);
+	spin_lock_init(&tcp_ses->mid_counter_lock);
 	INIT_LIST_HEAD(&tcp_ses->tcp_ses_list);
 	INIT_LIST_HEAD(&tcp_ses->smb_ses_list);
 	INIT_DELAYED_WORK(&tcp_ses->echo, cifs_echo_request);

fs/smb/client/smb1ops.c

@@ -169,10 +169,9 @@ cifs_get_next_mid(struct TCP_Server_Info *server)
 	__u16 last_mid, cur_mid;
 	bool collision, reconnect = false;
 
-	spin_lock(&server->mid_queue_lock);
-
+	spin_lock(&server->mid_counter_lock);
 	/* mid is 16 bit only for CIFS/SMB */
-	cur_mid = (__u16)((server->CurrentMid) & 0xffff);
+	cur_mid = (__u16)((server->current_mid) & 0xffff);
 	/* we do not want to loop forever */
 	last_mid = cur_mid;
 	cur_mid++;
@@ -198,6 +197,7 @@ cifs_get_next_mid(struct TCP_Server_Info *server)
 			cur_mid++;
 
 		num_mids = 0;
+		spin_lock(&server->mid_queue_lock);
 		list_for_each_entry(mid_entry, &server->pending_mid_q, qhead) {
 			++num_mids;
 			if (mid_entry->mid == cur_mid &&
@@ -207,6 +207,7 @@ cifs_get_next_mid(struct TCP_Server_Info *server)
 				break;
 			}
 		}
+		spin_unlock(&server->mid_queue_lock);
 
 		/*
 		 * if we have more than 32k mids in the list, then something
@@ -223,12 +224,12 @@ cifs_get_next_mid(struct TCP_Server_Info *server)
 
 		if (!collision) {
 			mid = (__u64)cur_mid;
-			server->CurrentMid = mid;
+			server->current_mid = mid;
 			break;
 		}
 		cur_mid++;
 	}
-	spin_unlock(&server->mid_queue_lock);
+	spin_unlock(&server->mid_counter_lock);
 
 	if (reconnect) {
 		cifs_signal_cifsd_for_reconnect(server, false);

fs/smb/client/smb2ops.c

@@ -91,7 +91,7 @@ smb2_add_credits(struct TCP_Server_Info *server,
 	if (*val > 65000) {
 		*val = 65000; /* Don't get near 64K credits, avoid srv bugs */
 		pr_warn_once("server overflowed SMB3 credits\n");
-		trace_smb3_overflow_credits(server->CurrentMid,
+		trace_smb3_overflow_credits(server->current_mid,
 					    server->conn_id, server->hostname, *val,
 					    add, server->in_flight);
 	}
@@ -136,15 +136,15 @@ smb2_add_credits(struct TCP_Server_Info *server,
 	wake_up(&server->request_q);
 
 	if (reconnect_detected) {
-		trace_smb3_reconnect_detected(server->CurrentMid,
+		trace_smb3_reconnect_detected(server->current_mid,
 			server->conn_id, server->hostname, scredits, add, in_flight);
 
 		cifs_dbg(FYI, "trying to put %d credits from the old server instance %d\n",
 			 add, instance);
 	}
 
 	if (reconnect_with_invalid_credits) {
-		trace_smb3_reconnect_with_invalid_credits(server->CurrentMid,
+		trace_smb3_reconnect_with_invalid_credits(server->current_mid,
 			server->conn_id, server->hostname, scredits, add, in_flight);
 		cifs_dbg(FYI, "Negotiate operation when server credits is non-zero. Optype: %d, server credits: %d, credits added: %d\n",
 			 optype, scredits, add);
@@ -176,7 +176,7 @@ smb2_add_credits(struct TCP_Server_Info *server,
 		break;
 	}
 
-	trace_smb3_add_credits(server->CurrentMid,
+	trace_smb3_add_credits(server->current_mid,
 			server->conn_id, server->hostname, scredits, add, in_flight);
 	cifs_dbg(FYI, "%s: added %u credits total=%d\n", __func__, add, scredits);
 }
@@ -203,7 +203,7 @@ smb2_set_credits(struct TCP_Server_Info *server, const int val)
 	in_flight = server->in_flight;
 	spin_unlock(&server->req_lock);
 
-	trace_smb3_set_credits(server->CurrentMid,
+	trace_smb3_set_credits(server->current_mid,
 			server->conn_id, server->hostname, scredits, val, in_flight);
 	cifs_dbg(FYI, "%s: set %u credits\n", __func__, val);
 
@@ -288,7 +288,7 @@ smb2_wait_mtu_credits(struct TCP_Server_Info *server, size_t size,
 	in_flight = server->in_flight;
 	spin_unlock(&server->req_lock);
 
-	trace_smb3_wait_credits(server->CurrentMid,
+	trace_smb3_wait_credits(server->current_mid,
 			server->conn_id, server->hostname, scredits, -(credits->value), in_flight);
 	cifs_dbg(FYI, "%s: removed %u credits total=%d\n",
 			__func__, credits->value, scredits);
@@ -316,7 +316,7 @@ smb2_adjust_credits(struct TCP_Server_Info *server,
 				      server->credits, server->in_flight,
 				      new_val - credits->value,
 				      cifs_trace_rw_credits_no_adjust_up);
-		trace_smb3_too_many_credits(server->CurrentMid,
+		trace_smb3_too_many_credits(server->current_mid,
 				server->conn_id, server->hostname, 0, credits->value - new_val, 0);
 		cifs_server_dbg(VFS, "R=%x[%x] request has less credits (%d) than required (%d)",
 				subreq->rreq->debug_id, subreq->subreq.debug_index,
@@ -338,7 +338,7 @@ smb2_adjust_credits(struct TCP_Server_Info *server,
 				      server->credits, server->in_flight,
 				      new_val - credits->value,
 				      cifs_trace_rw_credits_old_session);
-		trace_smb3_reconnect_detected(server->CurrentMid,
+		trace_smb3_reconnect_detected(server->current_mid,
 			server->conn_id, server->hostname, scredits,
 			credits->value - new_val, in_flight);
 		cifs_server_dbg(VFS, "R=%x[%x] trying to return %d credits to old session\n",
@@ -358,7 +358,7 @@ smb2_adjust_credits(struct TCP_Server_Info *server,
 	spin_unlock(&server->req_lock);
 	wake_up(&server->request_q);
 
-	trace_smb3_adj_credits(server->CurrentMid,
+	trace_smb3_adj_credits(server->current_mid,
 			server->conn_id, server->hostname, scredits,
 			credits->value - new_val, in_flight);
 	cifs_dbg(FYI, "%s: adjust added %u credits total=%d\n",
@@ -374,19 +374,19 @@ smb2_get_next_mid(struct TCP_Server_Info *server)
 {
 	__u64 mid;
 	/* for SMB2 we need the current value */
-	spin_lock(&server->mid_queue_lock);
-	mid = server->CurrentMid++;
-	spin_unlock(&server->mid_queue_lock);
+	spin_lock(&server->mid_counter_lock);
+	mid = server->current_mid++;
+	spin_unlock(&server->mid_counter_lock);
 	return mid;
 }
 
 static void
 smb2_revert_current_mid(struct TCP_Server_Info *server, const unsigned int val)
 {
-	spin_lock(&server->mid_queue_lock);
-	if (server->CurrentMid >= val)
-		server->CurrentMid -= val;
-	spin_unlock(&server->mid_queue_lock);
+	spin_lock(&server->mid_counter_lock);
+	if (server->current_mid >= val)
+		server->current_mid -= val;
+	spin_unlock(&server->mid_counter_lock);
 }
 
 static struct mid_q_entry *
@@ -460,9 +460,9 @@ smb2_negotiate(const unsigned int xid,
 {
 	int rc;
 
-	spin_lock(&server->mid_queue_lock);
-	server->CurrentMid = 0;
-	spin_unlock(&server->mid_queue_lock);
+	spin_lock(&server->mid_counter_lock);
+	server->current_mid = 0;
+	spin_unlock(&server->mid_counter_lock);
 	rc = SMB2_negotiate(xid, ses, server);
 	return rc;
 }
@@ -2498,7 +2498,7 @@ smb2_is_status_pending(char *buf, struct TCP_Server_Info *server)
 		spin_unlock(&server->req_lock);
 		wake_up(&server->request_q);
 
-		trace_smb3_pend_credits(server->CurrentMid,
+		trace_smb3_pend_credits(server->current_mid,
 				server->conn_id, server->hostname, scredits,
 				le16_to_cpu(shdr->CreditRequest), in_flight);
 		cifs_dbg(FYI, "%s: status pending add %u credits total=%d\n",

fs/smb/client/transport.c

@@ -397,7 +397,7 @@ __smb_send_rqst(struct TCP_Server_Info *server, int num_rqst,
 		 * socket so the server throws away the partial SMB
 		 */
 		cifs_signal_cifsd_for_reconnect(server, false);
-		trace_smb3_partial_send_reconnect(server->CurrentMid,
+		trace_smb3_partial_send_reconnect(server->current_mid,
 						  server->conn_id, server->hostname);
 	}
 smbd_done:
@@ -509,7 +509,7 @@ wait_for_free_credits(struct TCP_Server_Info *server, const int num_credits,
 		in_flight = server->in_flight;
 		spin_unlock(&server->req_lock);
 
-		trace_smb3_nblk_credits(server->CurrentMid,
+		trace_smb3_nblk_credits(server->current_mid,
 				server->conn_id, server->hostname, scredits, -1, in_flight);
 		cifs_dbg(FYI, "%s: remove %u credits total=%d\n",
 				__func__, 1, scredits);
@@ -542,7 +542,7 @@ wait_for_free_credits(struct TCP_Server_Info *server, const int num_credits,
 				in_flight = server->in_flight;
 				spin_unlock(&server->req_lock);
 
-				trace_smb3_credit_timeout(server->CurrentMid,
+				trace_smb3_credit_timeout(server->current_mid,
 						server->conn_id, server->hostname, scredits,
 						num_credits, in_flight);
 				cifs_server_dbg(VFS, "wait timed out after %d ms\n",
@@ -585,7 +585,7 @@ wait_for_free_credits(struct TCP_Server_Info *server, const int num_credits,
 					spin_unlock(&server->req_lock);
 
 					trace_smb3_credit_timeout(
-							server->CurrentMid,
+							server->current_mid,
 							server->conn_id, server->hostname,
 							scredits, num_credits, in_flight);
 					cifs_server_dbg(VFS, "wait timed out after %d ms\n",
@@ -615,7 +615,7 @@ wait_for_free_credits(struct TCP_Server_Info *server, const int num_credits,
 			in_flight = server->in_flight;
 			spin_unlock(&server->req_lock);
 
-			trace_smb3_waitff_credits(server->CurrentMid,
+			trace_smb3_waitff_credits(server->current_mid,
 					server->conn_id, server->hostname, scredits,
 					-(num_credits), in_flight);
 			cifs_dbg(FYI, "%s: remove %u credits total=%d\n",
@@ -666,7 +666,7 @@ wait_for_compound_request(struct TCP_Server_Info *server, int num,
 		 */
 		if (server->in_flight == 0) {
 			spin_unlock(&server->req_lock);
-			trace_smb3_insufficient_credits(server->CurrentMid,
+			trace_smb3_insufficient_credits(server->current_mid,
 					server->conn_id, server->hostname, scredits,
 					num, in_flight);
 			cifs_dbg(FYI, "%s: %d requests in flight, needed %d total=%d\n",