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.

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>

1 files changed, 2 insertions, 2 deletions

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index f9711c520269..213dfc10b783 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -553,14 +553,14 @@ 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;