[CIFS] Fix oops when slow oplock process races with unmount

If a tcon is being freed in call tconInfoFree, clean up any entries that may
exist in global oplock queue as the tcon structure hanging off of those entries
will be invalid and can cause oops while accesing any elements in the
tcon structure.
Signed-off-by: Shirish Pargaonkar <shirishp@us.ibm.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

fs/cifs/cifsproto.h

@@ -84,6 +84,7 @@ extern __u16 GetNextMid(struct TCP_Server_Info *server);
 extern struct oplock_q_entry *AllocOplockQEntry(struct inode *, u16,
 						 struct cifsTconInfo *);
 extern void DeleteOplockQEntry(struct oplock_q_entry *);
+extern void DeleteTconOplockQEntries(struct cifsTconInfo *);
 extern struct timespec cifs_NTtimeToUnix(u64 utc_nanoseconds_since_1601);
 extern u64 cifs_UnixTimeToNT(struct timespec);
 extern __le64 cnvrtDosCifsTm(__u16 date, __u16 time);

fs/cifs/connect.c

@@ -3527,6 +3527,7 @@ cifs_umount(struct super_block *sb, struct cifs_sb_info *cifs_sb)
 			FreeXid(xid);
 			return 0;
 		}
+		DeleteTconOplockQEntries(cifs_sb->tcon);
 		tconInfoFree(cifs_sb->tcon);
 		if ((ses) && (ses->server)) {
 			/* save off task so we do not refer to ses later */

fs/cifs/transport.c

@@ -142,6 +142,24 @@ void DeleteOplockQEntry(struct oplock_q_entry *oplockEntry)
 	kmem_cache_free(cifs_oplock_cachep, oplockEntry);
 }
 
+
+void DeleteTconOplockQEntries(struct cifsTconInfo *tcon)
+{
+	struct oplock_q_entry *temp;
+
+	if (tcon == NULL)
+		return;
+
+	spin_lock(&GlobalMid_Lock);
+	list_for_each_entry(temp, &GlobalOplock_Q, qhead) {
+		if ((temp->tcon) && (temp->tcon == tcon)) {
+			list_del(&temp->qhead);
+			kmem_cache_free(cifs_oplock_cachep, temp);
+		}
+	}
+	spin_unlock(&GlobalMid_Lock);
+}
+
 int
 smb_send(struct socket *ssocket, struct smb_hdr *smb_buffer,
 	 unsigned int smb_buf_length, struct sockaddr *sin)