[PATCH] blk-iocost: fix very large vtime when iocg activate

[Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>]

When the first iocg activate after blk_iocost_init(), now->vnow
maybe smaller than ioc->margins.target, cause very large vtarget
since it's u64.

	vtarget = now->vnow - ioc->margins.target;
	atomic64_add(vtarget - vtime, &iocg->vtime);

Then the iocg's vtime will be very large too, larger than now->vnow.

Signed-off-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
---
 block/blk-iocost.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/block/blk-iocost.c b/block/blk-iocost.c
index 5019dff524a4..a2ee12175c49 100644
--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c
@@ -1248,7 +1248,7 @@ static bool iocg_activate(struct ioc_gq *iocg, struct ioc_now *now)
 {
 	struct ioc *ioc = iocg->ioc;
 	u64 last_period, cur_period;
-	u64 vtime, vtarget;
+	u64 vtime, vtarget = 0;
 	int i;
 
 	/*
@@ -1290,7 +1290,8 @@ static bool iocg_activate(struct ioc_gq *iocg, struct ioc_now *now)
 	 * Always start with the target budget. On deactivation, we throw away
 	 * anything above it.
 	 */
-	vtarget = now->vnow - ioc->margins.target;
+	if (now->vnow > ioc->margins.target)
+		vtarget = now->vnow - ioc->margins.target;
 	vtime = atomic64_read(&iocg->vtime);
 
 	atomic64_add(vtarget - vtime, &iocg->vtime);
-- 
2.36.1