cifs: lock chan_lock outside match_session

Coverity had rightly indicated a possible deadlock
due to chan_lock being done inside match_session.
All callers of match_* functions should pick up the
necessary locks and call them.
Signed-off-by: Shyam Prasad N <sprasad@microsoft.com>
Reviewed-by: Paulo Alcantara (SUSE) <pc@manguebit.com>
Cc: stable@vger.kernel.org
Fixes: 724244cd ("cifs: protect session channel fields with chan_lock")
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/connect.c

@@ -1721,7 +1721,7 @@ cifs_get_tcp_session(struct smb3_fs_context *ctx,
 	return ERR_PTR(rc);
 }
 
-/* this function must be called with ses_lock held */
+/* this function must be called with ses_lock and chan_lock held */
 static int match_session(struct cifs_ses *ses, struct smb3_fs_context *ctx)
 {
 	if (ctx->sectype != Unspecified &&
@@ -1732,12 +1732,8 @@ static int match_session(struct cifs_ses *ses, struct smb3_fs_context *ctx)
 	 * If an existing session is limited to less channels than
 	 * requested, it should not be reused
 	 */
-	spin_lock(&ses->chan_lock);
-	if (ses->chan_max < ctx->max_channels) {
-		spin_unlock(&ses->chan_lock);
+	if (ses->chan_max < ctx->max_channels)
 		return 0;
-	}
-	spin_unlock(&ses->chan_lock);
 
 	switch (ses->sectype) {
 	case Kerberos:
@@ -1865,10 +1861,13 @@ cifs_find_smb_ses(struct TCP_Server_Info *server, struct smb3_fs_context *ctx)
 			spin_unlock(&ses->ses_lock);
 			continue;
 		}
+		spin_lock(&ses->chan_lock);
 		if (!match_session(ses, ctx)) {
+			spin_unlock(&ses->chan_lock);
 			spin_unlock(&ses->ses_lock);
 			continue;
 		}
+		spin_unlock(&ses->chan_lock);
 		spin_unlock(&ses->ses_lock);
 
 		++ses->ses_count;
@@ -2693,6 +2692,7 @@ cifs_match_super(struct super_block *sb, void *data)
 
 	spin_lock(&tcp_srv->srv_lock);
 	spin_lock(&ses->ses_lock);
+	spin_lock(&ses->chan_lock);
 	spin_lock(&tcon->tc_lock);
 	if (!match_server(tcp_srv, ctx, dfs_super_cmp) ||
 	    !match_session(ses, ctx) ||
@@ -2705,6 +2705,7 @@ cifs_match_super(struct super_block *sb, void *data)
 	rc = compare_mount_options(sb, mnt_data);
 out:
 	spin_unlock(&tcon->tc_lock);
+	spin_unlock(&ses->chan_lock);
 	spin_unlock(&ses->ses_lock);
 	spin_unlock(&tcp_srv->srv_lock);