[RFC PATCH 20/31] cifs: Don't need state locking in smb2_get_mid_entry()

[David Howells <dhowells@xxxxxxxxxx>]

There's no need to get ->srv_lock or ->ses_lock in smb2_get_mid_entry() as
all that happens of relevance (to the lock) inside the locked sections is
the reading of one status value in each.

Replace the locking with READ_ONCE() and use a switch instead of a chain of
if-statements.

Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: Steve French <sfrench@xxxxxxxxx>
cc: Paulo Alcantara <pc@xxxxxxxxxxxxx>
cc: Shyam Prasad N <sprasad@xxxxxxxxxxxxx>
cc: Tom Talpey <tom@xxxxxxxxxx>
cc: linux-cifs@xxxxxxxxxxxxxxx
cc: netfs@xxxxxxxxxxxxxxx
cc: linux-fsdevel@xxxxxxxxxxxxxxx
---
 fs/smb/client/smb2transport.c | 46 +++++++++++++++--------------------
 1 file changed, 19 insertions(+), 27 deletions(-)

diff --git a/fs/smb/client/smb2transport.c b/fs/smb/client/smb2transport.c
index 7c60584a8544..7194082bb5ac 100644
--- a/fs/smb/client/smb2transport.c
+++ b/fs/smb/client/smb2transport.c
@@ -769,43 +769,35 @@ static int
 smb2_get_mid_entry(struct cifs_ses *ses, struct TCP_Server_Info *server,
 		   struct smb_message *smb)
 {
-	spin_lock(&server->srv_lock);
-	if (server->tcpStatus == CifsExiting) {
-		spin_unlock(&server->srv_lock);
+	switch (READ_ONCE(server->tcpStatus)) {
+	case CifsExiting:
 		return -ENOENT;
-	}
-
-	if (server->tcpStatus == CifsNeedReconnect) {
-		spin_unlock(&server->srv_lock);
+	case CifsNeedReconnect:
 		cifs_dbg(FYI, "tcp session dead - return to caller to retry\n");
 		return -EAGAIN;
+	case CifsNeedNegotiate:
+		if (smb->command_id != SMB2_NEGOTIATE)
+			return -EAGAIN;
+		break;
+	default:
+		break;
 	}
 
-	if (server->tcpStatus == CifsNeedNegotiate &&
-	    smb->command_id != SMB2_NEGOTIATE) {
-		spin_unlock(&server->srv_lock);
-		return -EAGAIN;
-	}
-	spin_unlock(&server->srv_lock);
-
-	spin_lock(&ses->ses_lock);
-	if (ses->ses_status == SES_NEW) {
+	switch (READ_ONCE(ses->ses_status)) {
+	case SES_NEW:
 		if (smb->command_id != SMB2_SESSION_SETUP &&
-		    smb->command_id != SMB2_NEGOTIATE) {
-			spin_unlock(&ses->ses_lock);
+		    smb->command_id != SMB2_NEGOTIATE)
 			return -EAGAIN;
-		}
-		/* else ok - we are setting up session */
-	}
-
-	if (ses->ses_status == SES_EXITING) {
-		if (smb->command_id != SMB2_LOGOFF) {
-			spin_unlock(&ses->ses_lock);
+			/* else ok - we are setting up session */
+		break;
+	case SES_EXITING:
+		if (smb->command_id != SMB2_LOGOFF)
 			return -EAGAIN;
-		}
 		/* else ok - we are shutting down the session */
+		break;
+	default:
+		break;
 	}
-	spin_unlock(&ses->ses_lock);
 
 	smb2_init_mid(smb, server);