regmap: debugfs: Don't sleep while atomic for fast_io regmaps

If a regmap has "fast_io" set then its lock function uses a spinlock.
That doesn't work so well with the functions:
* regmap_cache_only_write_file()
* regmap_cache_bypass_write_file()

Both of the above functions have the pattern:
1. Lock the regmap.
2. Call:
   debugfs_write_file_bool()
     copy_from_user()
       __might_fault()
         __might_sleep()

Let's reorder things a bit so that we do all of our sleepable
functions before we grab the lock.

Fixes: d3dc5430 ("regmap: debugfs: Allow writes to cache state settings")
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://lore.kernel.org/r/20200715164611.1.I35b3533e8a80efde0cec1cc70f71e1e74b2fa0da@changeidSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/base/regmap/regmap-debugfs.c

@@ -457,29 +457,31 @@ static ssize_t regmap_cache_only_write_file(struct file *file,
 {
 	struct regmap *map = container_of(file->private_data,
 					  struct regmap, cache_only);
-	ssize_t result;
-	bool was_enabled, require_sync = false;
+	bool new_val, require_sync = false;
 	int err;
 
-	map->lock(map->lock_arg);
+	err = kstrtobool_from_user(user_buf, count, &new_val);
+	/* Ignore malforned data like debugfs_write_file_bool() */
+	if (err)
+		return count;
 
-	was_enabled = map->cache_only;
+	err = debugfs_file_get(file->f_path.dentry);
+	if (err)
+		return err;
 
-	result = debugfs_write_file_bool(file, user_buf, count, ppos);
-	if (result < 0) {
-		map->unlock(map->lock_arg);
-		return result;
-	}
+	map->lock(map->lock_arg);
 
-	if (map->cache_only && !was_enabled) {
+	if (new_val && !map->cache_only) {
 		dev_warn(map->dev, "debugfs cache_only=Y forced\n");
 		add_taint(TAINT_USER, LOCKDEP_STILL_OK);
-	} else if (!map->cache_only && was_enabled) {
+	} else if (!new_val && map->cache_only) {
 		dev_warn(map->dev, "debugfs cache_only=N forced: syncing cache\n");
 		require_sync = true;
 	}
+	map->cache_only = new_val;
 
 	map->unlock(map->lock_arg);
+	debugfs_file_put(file->f_path.dentry);
 
 	if (require_sync) {
 		err = regcache_sync(map);
@@ -487,7 +489,7 @@ static ssize_t regmap_cache_only_write_file(struct file *file,
 			dev_err(map->dev, "Failed to sync cache %d\n", err);
 	}
 
-	return result;
+	return count;
 }
 
 static const struct file_operations regmap_cache_only_fops = {
@@ -502,28 +504,32 @@ static ssize_t regmap_cache_bypass_write_file(struct file *file,
 {
 	struct regmap *map = container_of(file->private_data,
 					  struct regmap, cache_bypass);
-	ssize_t result;
-	bool was_enabled;
+	bool new_val;
+	int err;
 
-	map->lock(map->lock_arg);
+	err = kstrtobool_from_user(user_buf, count, &new_val);
+	/* Ignore malforned data like debugfs_write_file_bool() */
+	if (err)
+		return count;
 
-	was_enabled = map->cache_bypass;
+	err = debugfs_file_get(file->f_path.dentry);
+	if (err)
+		return err;
 
-	result = debugfs_write_file_bool(file, user_buf, count, ppos);
-	if (result < 0)
-		goto out;
+	map->lock(map->lock_arg);
 
-	if (map->cache_bypass && !was_enabled) {
+	if (new_val && !map->cache_bypass) {
 		dev_warn(map->dev, "debugfs cache_bypass=Y forced\n");
 		add_taint(TAINT_USER, LOCKDEP_STILL_OK);
-	} else if (!map->cache_bypass && was_enabled) {
+	} else if (!new_val && map->cache_bypass) {
 		dev_warn(map->dev, "debugfs cache_bypass=N forced\n");
 	}
+	map->cache_bypass = new_val;
 
-out:
 	map->unlock(map->lock_arg);
+	debugfs_file_put(file->f_path.dentry);
 
-	return result;
+	return count;
 }
 
 static const struct file_operations regmap_cache_bypass_fops = {