[PATCH] regmap: debugfs: Fix a boot time crash with early regmap init

[Tero Kristo]

If called early enough, regmap_debugfs_init causes a crash, if the
fs subsystem does not have its mount cache created yet. Even if this
would work, the root node for the regmap debugfs is still missing,
thus postpone the regmap_debugfs_init in this case until the root
node is created. A special regmap_debugfs_early list is created for
this purpose which is parsed later in the boot.

Signed-off-by: Tero Kristo <t-kristo@xxxxxx>
---
 drivers/base/regmap/regmap-debugfs.c |   28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/drivers/base/regmap/regmap-debugfs.c b/drivers/base/regmap/regmap-debugfs.c
index de11eca..e2d8f03 100644
--- a/drivers/base/regmap/regmap-debugfs.c
+++ b/drivers/base/regmap/regmap-debugfs.c
@@ -15,10 +15,18 @@
 #include <linux/debugfs.h>
 #include <linux/uaccess.h>
 #include <linux/device.h>
+#include <linux/list.h>
 
 #include "internal.h"
 
+struct regmap_debugfs_node {
+	struct regmap *map;
+	const char *name;
+	struct list_head link;
+};
+
 static struct dentry *regmap_debugfs_root;
+static LIST_HEAD(regmap_debugfs_early);
 
 /* Calculate the length of a fixed format  */
 static size_t regmap_calc_reg_len(int max_val, char *buf, size_t buf_size)
@@ -465,6 +473,18 @@ void regmap_debugfs_init(struct regmap *map, const char *name)
 	struct rb_node *next;
 	struct regmap_range_node *range_node;
 
+	/* If we don't have the debugfs root yet, postpone init */
+	if (!regmap_debugfs_root) {
+		struct regmap_debugfs_node *node;
+		node = kzalloc(sizeof(*node), GFP_KERNEL);
+		if (!node)
+			return;
+		node->map = map;
+		node->name = name;
+		list_add(&node->link, &regmap_debugfs_early);
+		return;
+	}
+
 	INIT_LIST_HEAD(&map->debugfs_off_cache);
 	mutex_init(&map->cache_lock);
 
@@ -528,9 +548,17 @@ void regmap_debugfs_exit(struct regmap *map)
 
 void regmap_debugfs_initcall(void)
 {
+	struct regmap_debugfs_node *node, *tmp;
+
 	regmap_debugfs_root = debugfs_create_dir("regmap", NULL);
 	if (!regmap_debugfs_root) {
 		pr_warn("regmap: Failed to create debugfs root\n");
 		return;
 	}
+
+	list_for_each_entry_safe(node, tmp, &regmap_debugfs_early, link) {
+		regmap_debugfs_init(node->map, node->name);
+		list_del(&node->link);
+		kfree(node);
+	}
 }
-- 
1.7.9.5

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