linux-kernel - [PATCH block/for-5.6-fixes] blk-iocost: fix incorrect vtime comparison in iocg_is

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Message-ID: <20200310170746.GD79873@mtj.duckdns.org>
Date:   Tue, 10 Mar 2020 13:07:46 -0400
From:   Tejun Heo <tj@...nel.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH block/for-5.6-fixes] blk-iocost: fix incorrect vtime
 comparison in iocg_is_idle()

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: Tejun Heo <tj@...nel.org>
Fixes: 7caa47151ab2 ("blkcg: implement blk-iocost")
Cc: stable@...r.kernel.org # v5.4+
---
 block/blk-iocost.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/blk-iocost.c b/block/blk-iocost.c
index 27ca68621137..9a599cc28c29 100644
--- a/block/blk-iocost.c
+++ b/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;