[PATCH 2/2] mtd: call external _get and _put in right order

Alexander Usyskin
2023-06-20T13:20:17Z

MTD provider provides mtd_info object to mtd subsystem.
With kref patch the mtd_info object can be alive after
provider released mtd device.
Fix calling order in _get and _put functions to allow
mtd provider to safely alloc and release mtd object.

Execute:
1) call external _get
2) get_module
3) add internal kref
in the get function and opposite order in the put one.

The _put_device callback should be the last in put
as the master struct memory may be freed in this callback.

Signed-off-by: Alexander Usyskin <alexander.usyskin@intel.com>
---
drivers/mtd/mtdcore.c | 28 ++++++++++++++--------------
1 file changed, 14 insertions(+), 14 deletions(-)

diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
index 84bd1878367d..a5bc60013edf 100644
--- a/drivers/mtd/mtdcore.c
+++ b/drivers/mtd/mtdcore.c
@@ -1227,21 +1227,20 @@ int __get_mtd_device(struct mtd_info *mtd)
struct mtd_info *master = mtd_get_master(mtd);
int err;

- if (!try_module_get(master->owner))
- return -ENODEV;
-
- kref_get(&mtd->refcnt);
-
if (master->_get_device) {
err = master->_get_device(mtd);
-
- if (err) {
- kref_put(&mtd->refcnt, mtd_device_release);
- module_put(master->owner);
+ if (err)
return err;
- }
}

+ if (!try_module_get(master->owner)) {
+ if (master->_put_device)
+ master->_put_device(master);
+ return -ENODEV;
+ }
+
+ kref_get(&mtd->refcnt);
+
while (mtd->parent) {
if (IS_ENABLED(CONFIG_MTD_PARTITIONED_MASTER) || mtd->parent != master)
kref_get(&mtd->parent->refcnt);
@@ -1338,13 +1337,14 @@ void __put_mtd_device(struct mtd_info *mtd)
mtd = parent;
}

- if (master->_put_device)
- master->_put_device(master);
+ if (IS_ENABLED(CONFIG_MTD_PARTITIONED_MASTER))
+ kref_put(&master->refcnt, mtd_device_release);

module_put(master->owner);

- if (IS_ENABLED(CONFIG_MTD_PARTITIONED_MASTER))
- kref_put(&master->refcnt, mtd_device_release);
+ /* must be the last as master can be freed in the _put_device */
+ if (master->_put_device)
+ master->_put_device(master);
}
EXPORT_SYMBOL_GPL(__put_mtd_device);

--
2.34.1