drivers/block/zram/zram_drv.c: do not keep dangling zcomp pointer after zram reset

We do all reset operations under write lock, so we don't need to save
->disksize and ->comp to stack variables.  Another thing is that ->comp is
freed during zram reset, but comp pointer is not NULL-ed, so zram keeps
the freed pointer value.

Link: https://lkml.kernel.org/r/20220824035100.971816-1-senozhatsky@chromium.orgSigned-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

drivers/block/zram/zram_drv.c

@@ -1710,9 +1710,6 @@ static int zram_rw_page(struct block_device *bdev, sector_t sector,
 
 static void zram_reset_device(struct zram *zram)
 {
-	struct zcomp *comp;
-	u64 disksize;
-
 	down_write(&zram->init_lock);
 
 	zram->limit_pages = 0;
@@ -1722,17 +1719,15 @@ static void zram_reset_device(struct zram *zram)
 		return;
 	}
 
-	comp = zram->comp;
-	disksize = zram->disksize;
-	zram->disksize = 0;
-
 	set_capacity_and_notify(zram->disk, 0);
 	part_stat_set_all(zram->disk->part0, 0);
 
 	/* I/O operation under all of CPU are done so let's free */
-	zram_meta_free(zram, disksize);
+	zram_meta_free(zram, zram->disksize);
+	zram->disksize = 0;
 	memset(&zram->stats, 0, sizeof(zram->stats));
-	zcomp_destroy(comp);
+	zcomp_destroy(zram->comp);
+	zram->comp = NULL;
 	reset_bdev(zram);
 
 	up_write(&zram->init_lock);