[PATCH] mtd: take a reference when opening an unpartitioned master

[James Hilliard <james.hilliard1@gmail.com>]

CONFIG_MTD_PARTITIONED_MASTER controls whether a master is registered
alongside its partitions. Without that option, an unpartitioned device
is still registered as a master and can be opened directly.

__get_mtd_device() skips the master while walking the parent chain and
only takes its reference when CONFIG_MTD_PARTITIONED_MASTER is enabled.
A direct open therefore leaves the registration reference as the sole
reference. Unregistering the device releases its device-model and NVMEM
state while the handle remains open.

Take and release the master reference for direct opens as well. Retain
the existing behavior for partition handles whose master is not
registered. Decide from the original handle before walking the parent
chain so get and put use the same condition.

Fixes: 264725e35fbc ("mtd: Clean refcounting with MTD_PARTITIONED_MASTER")
Cc: stable@vger.kernel.org
Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
---
 drivers/mtd/mtdcore.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
index 491a27d0315f..444615804236 100644
--- a/drivers/mtd/mtdcore.c
+++ b/drivers/mtd/mtdcore.c
@@ -1330,6 +1330,7 @@ EXPORT_SYMBOL_GPL(get_mtd_device);
 int __get_mtd_device(struct mtd_info *mtd)
 {
 	struct mtd_info *master = mtd_get_master(mtd);
+	bool master_ref = mtd == master || IS_ENABLED(CONFIG_MTD_PARTITIONED_MASTER);
 	int err;
 
 	if (master->_get_device) {
@@ -1350,7 +1351,7 @@ int __get_mtd_device(struct mtd_info *mtd)
 		mtd = mtd->parent;
 	}
 
-	if (IS_ENABLED(CONFIG_MTD_PARTITIONED_MASTER))
+	if (master_ref)
 		kref_get(&master->refcnt);
 
 	return 0;
@@ -1435,6 +1436,7 @@ EXPORT_SYMBOL_GPL(put_mtd_device);
 void __put_mtd_device(struct mtd_info *mtd)
 {
 	struct mtd_info *master = mtd_get_master(mtd);
+	bool master_ref = mtd == master || IS_ENABLED(CONFIG_MTD_PARTITIONED_MASTER);
 
 	while (mtd) {
 		/* kref_put() can relese mtd, so keep a reference mtd->parent */
@@ -1445,7 +1447,7 @@ void __put_mtd_device(struct mtd_info *mtd)
 		mtd = parent;
 	}
 
-	if (IS_ENABLED(CONFIG_MTD_PARTITIONED_MASTER))
+	if (master_ref)
 		kref_put(&master->refcnt, mtd_device_release);
 
 	module_put(master->owner);

---
base-commit: 1c1a342aceec79528b3ba51f376eca2be5928fe7
change-id: 20261108-submit-mtd-master-open-reference-v1-a1b756dcde47

Best regards,
--  
James Hilliard <james.hilliard1@gmail.com>