vfs: remove dentry of a destination after rename()

If dentry has elevated reference count during rename (a file is opened
for instance) it is not destroyed and remains in the dentry hash. As a
result old file is accessible by destination path instead of new one.

Signed-off-by: Gleb Natapov <gleb@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>

fs/vfs/vfs.h

@@ -140,6 +140,7 @@ int	 fs_noop(void);
 
 struct dentry *dentry_alloc(struct dentry *parent_dp, struct vnode *vp, const char *path);
 void dentry_move(struct dentry *dp, struct dentry *parent_dp, char *path);
+void dentry_remove(struct dentry *dp);
 void	dref(struct dentry *dp);
 void	drele(struct dentry *dp);
 

fs/vfs/vfs_lookup.c

@@ -39,6 +39,7 @@
 #define DENTRY_BUCKETS 32
 
 static LIST_HEAD(dentry_hash_head, dentry) dentry_hash_table[DENTRY_BUCKETS];
+static LIST_HEAD(fake, dentry) fake;
 static struct mutex dentry_hash_lock;
 
 /*
@@ -129,6 +130,16 @@ dentry_move(struct dentry *dp, struct dentry *parent_dp, char *path)
     free(old_path);
 }
 
+void
+dentry_remove(struct dentry *dp)
+{
+    mutex_lock(&dentry_hash_lock);
+    LIST_REMOVE(dp, d_link);
+    /* put it on a fake list for drele() to work*/
+    LIST_INSERT_HEAD(&fake, dp, d_link);
+    mutex_unlock(&dentry_hash_lock);
+}
+
 void
 dref(struct dentry *dp)
 {

fs/vfs/vfs_syscalls.cc

@@ -722,6 +722,8 @@ sys_rename(char *src, char *dest)
 	error = VOP_RENAME(dvp1, vp1, sname, dvp2, vp2, dname);
 
 	dentry_move(dp1, ddp2, dname);
+	if (dp2)
+		dentry_remove(dp2);
 
  err4:
 	vn_unlock(dvp2);