of: overlay: Call of_changeset_init() early

When of_overlay_fdt_apply() fails, the changeset may be partially
applied, and the caller is still expected to call of_overlay_remove() to
clean up this partial state.

However, of_overlay_apply() calls of_resolve_phandles() before
init_overlay_changeset().  Hence if the overlay fails to apply due to an
unresolved symbol, the overlay_changeset.cset.entries list is still
uninitialized, and cleanup will crash with a NULL-pointer dereference in
overlay_removal_is_ok().

Fix this by moving the call to of_changeset_init() from
init_overlay_changeset() to of_overlay_fdt_apply(), where all other
early initialization is done.

Fixes: f948d6d ("of: overlay: avoid race condition between applying multiple overlays")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/4f1d6d74b61cba2599026adb6d1948ae559ce91f.1690533838.git.geert+renesas@glider.be
Signed-off-by: Rob Herring <robh@kernel.org>

Author: geertu

drivers/of/overlay.c

@@ -769,8 +769,6 @@ static int init_overlay_changeset(struct overlay_changeset *ovcs,
 	if (!of_node_is_root(ovcs->overlay_root))
 		pr_debug("%s() ovcs->overlay_root is not root\n", __func__);
 
-	of_changeset_init(&ovcs->cset);
-
 	cnt = 0;
 
 	/* fragment nodes */
@@ -1033,6 +1031,7 @@ int of_overlay_fdt_apply(const void *overlay_fdt, u32 overlay_fdt_size,
 
 	INIT_LIST_HEAD(&ovcs->ovcs_list);
 	list_add_tail(&ovcs->ovcs_list, &ovcs_list);
+	of_changeset_init(&ovcs->cset);
 
 	/*
 	 * Must create permanent copy of FDT because of_fdt_unflatten_tree()