blk-iocost: fix incorrect vtime comparison in iocg_is_idle()

mainline inclusion
from mainline-5.6-rc6
commit dcd6589b11d3b1e71f516a87a7b9646ed356b4c0
category: feature
bugzilla: 38688
CVE: NA

---------------------------

vtimes may wrap and time_before/after64() should be used to determine
whether a given vtime is before or after another. iocg_is_idle() was
incorrectly using plain "<" comparison do determine whether done_vtime
is before vtime. Here, the only thing we're interested in is whether
done_vtime matches vtime which indicates that there's nothing in
flight. Let's test for inequality instead.
Signed-off-by: NTejun Heo <tj@kernel.org>
Fixes: 7caa47151ab2 ("blkcg: implement blk-iocost")
Cc: stable@vger.kernel.org # v5.4+
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NYu Kuai <yukuai3@huawei.com>
Reviewed-by: NHou Tao <houtao1@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

block/blk-iocost.c

@@ -1318,7 +1318,7 @@ static bool iocg_is_idle(struct ioc_gq *iocg)
 		return false;
 
 	/* is something in flight? */
-	if (atomic64_read(&iocg->done_vtime) < atomic64_read(&iocg->vtime))
+	if (atomic64_read(&iocg->done_vtime) != atomic64_read(&iocg->vtime))
 		return false;
 
 	return true;