[PATCH v2] ubi: don't decrease ubi->ref_count on detach error

[Daniel Golle]

If attempting to detach a UBI device while it is still busy, detaching
is refused. However, the reference counter is still being decreased
despite the error. Rework detach function to only decrease the reference
counter once all conditions for detachment are met.

Fixes: cdfa788acd13 ("UBI: prepare attach and detach functions")
Signed-off-by: Daniel Golle <daniel at makrotopia.org>
---
v2: also catch negative ref_count and add ubi_assert as suggested

 drivers/mtd/ubi/build.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/mtd/ubi/build.c b/drivers/mtd/ubi/build.c
index 7d4ff1193db6f..2316f6014c7f5 100644
--- a/drivers/mtd/ubi/build.c
+++ b/drivers/mtd/ubi/build.c
@@ -1099,16 +1099,17 @@ int ubi_detach_mtd_dev(int ubi_num, int anyway)
 
 	spin_lock(&ubi_devices_lock);
 	put_device(&ubi->dev);
-	ubi->ref_count -= 1;
-	if (ubi->ref_count) {
+	if (ubi->ref_count != 1) {
 		if (!anyway) {
 			spin_unlock(&ubi_devices_lock);
 			return -EBUSY;
 		}
 		/* This may only happen if there is a bug */
 		ubi_err(ubi, "%s reference count %d, destroy anyway",
-			ubi->ubi_name, ubi->ref_count);
+			ubi->ubi_name, ubi->ref_count - 1);
 	}
+	ubi->ref_count -= 1;
+	ubi_assert(ubi->ref_count == 0);
 	ubi_devices[ubi_num] = NULL;
 	spin_unlock(&ubi_devices_lock);
 
-- 
2.43.0