linux-kernel - [PATCH] block:zram: do not keep dangling zcomp pointer after zram reset

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Message-Id: <20220824035100.971816-1-senozhatsky@chromium.org>
Date:   Wed, 24 Aug 2022 12:51:00 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Minchan Kim <minchan@...nel.org>
Cc:     Nitin Gupta <ngupta@...are.org>, linux-kernel@...r.kernel.org,
        linux-block@...r.kernel.org,
        Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: [PATCH] block:zram: 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.

Signed-off-by: Sergey Senozhatsky <senozhatsky@...omium.org>
---
 drivers/block/zram/zram_drv.c | 13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 0c8c211f051f..4fc99c5667ef 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1721,9 +1721,6 @@ 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;
@@ -1733,17 +1730,15 @@ 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);
-- 
2.37.2.609.g9ff673ca1a-goog