On Mon, Jan 13, 2014 at 03:55:27PM -0800, Andrew Morton wrote:

On Mon, 13 Jan 2014 20:18:56 +0900 Minchan Kim [off-list ref] wrote:

quoted

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.

..

--- 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;

This makes zram.lock nest inside zram.init_lock, which afaict is new
behaviour.

Originally, it was nested so it's not new. :)
Look at zram_make_request which hold init_lock and then zram_bvec_rw
hold zram->lock.

That all seems OK and logical - has it been well tested with lockdep?

Yeb.

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-- 
Kind regards,
Minchan Kim