mm/damon/dbgfs: fix memory leak when using debugfs_lookup()

When calling debugfs_lookup() the result must have dput() called on it,
otherwise the memory will leak over time.  Fix this up by properly calling
dput().

Link: https://lkml.kernel.org/r/20220902191149.112434-1-sj@kernel.org
Fixes: 75c1c2b5 ("mm/damon/dbgfs: support multiple contexts")
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/damon/dbgfs.c

@@ -884,6 +884,7 @@ static int dbgfs_rm_context(char *name)
 	struct dentry *root, *dir, **new_dirs;
 	struct damon_ctx **new_ctxs;
 	int i, j;
+	int ret = 0;
 
 	if (damon_nr_running_ctxs())
 		return -EBUSY;
@@ -898,14 +899,16 @@ static int dbgfs_rm_context(char *name)
 
 	new_dirs = kmalloc_array(dbgfs_nr_ctxs - 1, sizeof(*dbgfs_dirs),
 			GFP_KERNEL);
-	if (!new_dirs)
-		return -ENOMEM;
+	if (!new_dirs) {
+		ret = -ENOMEM;
+		goto out_dput;
+	}
 
 	new_ctxs = kmalloc_array(dbgfs_nr_ctxs - 1, sizeof(*dbgfs_ctxs),
 			GFP_KERNEL);
 	if (!new_ctxs) {
-		kfree(new_dirs);
-		return -ENOMEM;
+		ret = -ENOMEM;
+		goto out_new_dirs;
 	}
 
 	for (i = 0, j = 0; i < dbgfs_nr_ctxs; i++) {
@@ -925,7 +928,13 @@ static int dbgfs_rm_context(char *name)
 	dbgfs_ctxs = new_ctxs;
 	dbgfs_nr_ctxs--;
 
-	return 0;
+	goto out_dput;
+
+out_new_dirs:
+	kfree(new_dirs);
+out_dput:
+	dput(dir);
+	return ret;
 }
 
 static ssize_t dbgfs_rm_context_write(struct file *file,