smb: client: smb: client: eliminate mid_flags field

JIRA: https://issues.redhat.com/browse/RHEL-109507

commit 3fd8ec2
Author: Wang Zhaolong <[email protected]>
Date:   Mon Aug 4 21:40:05 2025 +0800

    smb: client: smb: client: eliminate mid_flags field

    This is step 3/4 of a patch series to fix mid_q_entry memory leaks
    caused by race conditions in callback execution.

    Replace the mid_flags bitmask with dedicated boolean fields to
    simplify locking logic and improve code readability:

    - Replace MID_DELETED with bool deleted_from_q
    - Replace MID_WAIT_CANCELLED with bool wait_cancelled
    - Remove mid_flags field entirely

    The new boolean fields have clearer semantics:
    - deleted_from_q: whether mid has been removed from pending_mid_q
    - wait_cancelled: whether request was cancelled during wait

    This change reduces memory usage (from 4-byte bitmask to 2 boolean
    flags) and eliminates confusion about which lock protects which
    flag bits, preparing for per-mid locking in the next patch.

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

Signed-off-by: Paulo Alcantara <[email protected]>

Author: pcacjr

fs/smb/client/cifsglob.h

@@ -1787,9 +1787,10 @@ struct mid_q_entry {
 	unsigned int resp_buf_size;
 	int mid_state;	/* wish this were enum but can not pass to wait_event */
 	int mid_rc;		/* rc for MID_RC */
-	unsigned int mid_flags;
 	__le16 command;		/* smb command code */
 	unsigned int optype;	/* operation type */
+	bool wait_cancelled:1;  /* Cancelled while waiting for response */
+	bool deleted_from_q:1;  /* Whether Mid has been dequeued frem pending_mid_q */
 	bool large_buf:1;	/* if valid response, is pointer to large buf */
 	bool multiRsp:1;	/* multiple trans2 responses for one request  */
 	bool multiEnd:1;	/* both received */
@@ -1951,10 +1952,6 @@ static inline bool is_replayable_error(int error)
 #define   MID_RESPONSE_READY 0x40 /* ready for other process handle the rsp */
 #define   MID_RC             0x80 /* mid_rc contains custom rc */
 
-/* Flags */
-#define   MID_WAIT_CANCELLED	 1 /* Cancelled while waiting for response */
-#define   MID_DELETED            2 /* Mid has been dequeued/deleted */
-
 /* Types of response buffer returned from SendReceive2 */
 #define   CIFS_NO_BUFFER        0    /* Response buffer not returned */
 #define   CIFS_SMALL_BUFFER     1
@@ -2066,7 +2063,7 @@ 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
- *				(any changes in mid_q_entry fields)
+ *				mid_q_entry->deleted_from_q
  * 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

fs/smb/client/connect.c

@@ -327,7 +327,7 @@ cifs_abort_connection(struct TCP_Server_Info *server)
 		if (mid->mid_state == MID_REQUEST_SUBMITTED)
 			mid->mid_state = MID_RETRY_NEEDED;
 		list_move(&mid->qhead, &retry_list);
-		mid->mid_flags |= MID_DELETED;
+		mid->deleted_from_q = true;
 	}
 	spin_unlock(&server->mid_queue_lock);
 	cifs_server_unlock(server);
@@ -890,7 +890,7 @@ is_smb_response(struct TCP_Server_Info *server, unsigned char type)
 			list_for_each_entry_safe(mid, nmid, &server->pending_mid_q, qhead) {
 				kref_get(&mid->refcount);
 				list_move(&mid->qhead, &dispose_list);
-				mid->mid_flags |= MID_DELETED;
+				mid->deleted_from_q = true;
 			}
 			spin_unlock(&server->mid_queue_lock);
 
@@ -968,12 +968,12 @@ dequeue_mid(struct mid_q_entry *mid, bool malformed)
 	 * Trying to handle/dequeue a mid after the send_recv()
 	 * function has finished processing it is a bug.
 	 */
-	if (mid->mid_flags & MID_DELETED) {
+	if (mid->deleted_from_q == true) {
 		spin_unlock(&mid->server->mid_queue_lock);
 		pr_warn_once("trying to dequeue a deleted mid\n");
 	} else {
 		list_del_init(&mid->qhead);
-		mid->mid_flags |= MID_DELETED;
+		mid->deleted_from_q = true;
 		spin_unlock(&mid->server->mid_queue_lock);
 	}
 }
@@ -1110,7 +1110,7 @@ clean_demultiplex_info(struct TCP_Server_Info *server)
 			kref_get(&mid_entry->refcount);
 			mid_entry->mid_state = MID_SHUTDOWN;
 			list_move(&mid_entry->qhead, &dispose_list);
-			mid_entry->mid_flags |= MID_DELETED;
+			mid_entry->deleted_from_q = true;
 		}
 		spin_unlock(&server->mid_queue_lock);
 

fs/smb/client/smb2ops.c

@@ -373,7 +373,7 @@ __smb2_find_mid(struct TCP_Server_Info *server, char *buf, bool dequeue)
 			kref_get(&mid->refcount);
 			if (dequeue) {
 				list_del_init(&mid->qhead);
-				mid->mid_flags |= MID_DELETED;
+				mid->deleted_from_q = true;
 			}
 			spin_unlock(&server->mid_queue_lock);
 			return mid;
@@ -4753,7 +4753,7 @@ static void smb2_decrypt_offload(struct work_struct *work)
 			} else {
 				spin_lock(&dw->server->mid_queue_lock);
 				mid->mid_state = MID_REQUEST_SUBMITTED;
-				mid->mid_flags &= ~(MID_DELETED);
+				mid->deleted_from_q = false;
 				list_add_tail(&mid->qhead,
 					&dw->server->pending_mid_q);
 				spin_unlock(&dw->server->mid_queue_lock);

fs/smb/client/transport.c

@@ -89,7 +89,7 @@ void __release_mid(struct kref *refcount)
 #endif
 	struct TCP_Server_Info *server = midEntry->server;
 
-	if (midEntry->resp_buf && (midEntry->mid_flags & MID_WAIT_CANCELLED) &&
+	if (midEntry->resp_buf && (midEntry->wait_cancelled) &&
 	    (midEntry->mid_state == MID_RESPONSE_RECEIVED ||
 	     midEntry->mid_state == MID_RESPONSE_READY) &&
 	    server->ops->handle_cancelled_mid)
@@ -161,9 +161,9 @@ void
 delete_mid(struct mid_q_entry *mid)
 {
 	spin_lock(&mid->server->mid_queue_lock);
-	if (!(mid->mid_flags & MID_DELETED)) {
+	if (mid->deleted_from_q == false) {
 		list_del_init(&mid->qhead);
-		mid->mid_flags |= MID_DELETED;
+		mid->deleted_from_q = true;
 	}
 	spin_unlock(&mid->server->mid_queue_lock);
 
@@ -925,9 +925,9 @@ cifs_sync_mid_result(struct mid_q_entry *mid, struct TCP_Server_Info *server)
 		rc = mid->mid_rc;
 		break;
 	default:
-		if (!(mid->mid_flags & MID_DELETED)) {
+		if (mid->deleted_from_q == false) {
 			list_del_init(&mid->qhead);
-			mid->mid_flags |= MID_DELETED;
+			mid->deleted_from_q = true;
 		}
 		spin_unlock(&server->mid_queue_lock);
 		cifs_server_dbg(VFS, "%s: invalid mid state mid=%llu state=%d\n",
@@ -1241,7 +1241,7 @@ compound_send_recv(const unsigned int xid, struct cifs_ses *ses,
 				 midQ[i]->mid, le16_to_cpu(midQ[i]->command));
 			send_cancel(server, &rqst[i], midQ[i]);
 			spin_lock(&server->mid_queue_lock);
-			midQ[i]->mid_flags |= MID_WAIT_CANCELLED;
+			midQ[i]->wait_cancelled = true;
 			if (midQ[i]->mid_state == MID_REQUEST_SUBMITTED ||
 			    midQ[i]->mid_state == MID_RESPONSE_RECEIVED) {
 				midQ[i]->callback = cifs_cancelled_callback;