UBI: use separate mutex for volumes checking

Introduce a separate mutex which serializes volumes checking,
because we cammot really use volumes_mutex - it cases reverse
locking problems with mtd_tbl_mutex when gluebi is used -
thanks to lockdep.
Signed-off-by: NArtem Bityutskiy <Artem.Bityutskiy@nokia.com>

drivers/mtd/ubi/build.c

@@ -703,6 +703,7 @@ int ubi_attach_mtd_dev(struct mtd_info *mtd, int ubi_num, int vid_hdr_offset)
 		goto out_free;
 
 	mutex_init(&ubi->buf_mutex);
+	mutex_init(&ubi->ckvol_mutex);
 	ubi->peb_buf1 = vmalloc(ubi->peb_size);
 	if (!ubi->peb_buf1)
 		goto out_free;

drivers/mtd/ubi/kapi.c

@@ -169,17 +169,12 @@ struct ubi_volume_desc *ubi_open_volume(int ubi_num, int vol_id, int mode)
 	desc->vol = vol;
 	desc->mode = mode;
 
-	/*
-	 * To prevent simultaneous checks of the same volume we use
-	 * @volumes_mutex, although it is not the purpose it was introduced
-	 * for.
-	 */
-	mutex_lock(&ubi->volumes_mutex);
+	mutex_lock(&ubi->ckvol_mutex);
 	if (!vol->checked) {
 		/* This is the first open - check the volume */
 		err = ubi_check_volume(ubi, vol_id);
 		if (err < 0) {
-			mutex_unlock(&ubi->volumes_mutex);
+			mutex_unlock(&ubi->ckvol_mutex);
 			ubi_close_volume(desc);
 			return ERR_PTR(err);
 		}
@@ -190,7 +185,7 @@ struct ubi_volume_desc *ubi_open_volume(int ubi_num, int vol_id, int mode)
 		}
 		vol->checked = 1;
 	}
-	mutex_unlock(&ubi->volumes_mutex);
+	mutex_unlock(&ubi->ckvol_mutex);
 
 	return desc;
 

drivers/mtd/ubi/ubi.h

@@ -392,6 +392,7 @@ struct ubi_device {
 	void *peb_buf1;
 	void *peb_buf2;
 	struct mutex buf_mutex;
+	struct mutex ckvol_mutex;
 #ifdef CONFIG_MTD_UBI_DEBUG
 	void *dbg_peb_buf;
 	struct mutex dbg_buf_mutex;