mtd: core: don't remove debugfs directory if device is in use

Previously, if del_mtd_device() failed with -EBUSY due to a non-zero
usecount, a subsequent call to attempt the deletion again would try to
remove a debugfs directory that had already been removed and panic.
With this change the second call can instead proceed safely.

Fixes: e8e3edb9 ("mtd: create per-device and module-scope debugfs entries")
Signed-off-by: Zev Weiss <zev@bewilderbeest.net>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20211014203953.5424-1-zev@bewilderbeest.net

drivers/mtd/mtdcore.c

@@ -724,8 +724,6 @@ int del_mtd_device(struct mtd_info *mtd)
 
 	mutex_lock(&mtd_table_mutex);
 
-	debugfs_remove_recursive(mtd->dbg.dfs_dir);
-
 	if (idr_find(&mtd_idr, mtd->index) != mtd) {
 		ret = -ENODEV;
 		goto out_error;
@@ -741,6 +739,8 @@ int del_mtd_device(struct mtd_info *mtd)
 		       mtd->index, mtd->name, mtd->usecount);
 		ret = -EBUSY;
 	} else {
+		debugfs_remove_recursive(mtd->dbg.dfs_dir);
+
 		/* Try to remove the NVMEM provider */
 		if (mtd->nvmem)
 			nvmem_unregister(mtd->nvmem);