zram: fix race between reset and flushing pending work

Dan and Sergey reported that there is a racy between reset and flushing
of pending work so that it could make oops by freeing zram->meta in
reset while zram_slot_free can access zram->meta if new request is
adding during the race window.

This patch moves flush after taking init_lock so it prevents new request
so that it closes the race.

Change-Id: Ibc09001d1ad4a4ef852d661384259b53f0f9c19b
Signed-off-by: Minchan Kim <minchan@kernel.org>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Jerome Marchand <jmarchan@redhat.com>
Tested-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 1a1dc60..a376109 100644 (file)
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -552,14 +552,14 @@ static void zram_reset_device(struct zram *zram, bool reset_capacity)
        size_t index;
        struct zram_meta *meta;
 
-       flush_work(&zram->free_work);
-
        down_write(&zram->init_lock);
        if (!zram->init_done) {
                up_write(&zram->init_lock);
                return;
        }
 
+       flush_work(&zram->free_work);
+
        meta = zram->meta;
        zram->init_done = 0;