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From:   linan666@huaweicloud.com
To:     tj@kernel.org, josef@toxicpanda.com, axboe@kernel.dk,
        yukuai3@huawei.com
Cc:     cgroups@vger.kernel.org, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org, linan122@huawei.com,
        yi.zhang@huawei.com, houtao1@huawei.com, yangerkun@huawei.com
Subject: [PATCH] blk-throttle: Calculate allowed value only when the throttle is enabled
Date:   Thu, 28 Sep 2023 09:58:58 +0800
Message-Id: <20230928015858.1809934-1-linan666@huaweicloud.com>
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From: Li Nan <linan122@huawei.com>

When the throttle of bps is not enabled, tg_bps_limit() returns U64_MAX,
which is be used in calculate_bytes_allowed(), and divide 0 error will
happen.

To fix it, only calculate allowed value when the throttle of bps/iops is
enabled and the value will be used.

Fixes: e8368b57c006 ("blk-throttle: use calculate_io/bytes_allowed() for throtl_trim_slice()")
Reported-by: Changhui Zhong <czhong@redhat.com>
Closes: https://lore.kernel.org/all/CAGVVp+Vt6idZtxfU9jF=VSbu145Wi-d-WnAZx_hEfOL8yLZgBA@mail.gmail.com
Signed-off-by: Li Nan <linan122@huawei.com>
---
 block/blk-throttle.c | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 38a881cf97d0..3c9a74ab9f0e 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -730,8 +730,10 @@ static u64 calculate_bytes_allowed(u64 bps_limit, unsigned long jiffy_elapsed)
 static inline void throtl_trim_slice(struct throtl_grp *tg, bool rw)
 {
 	unsigned long time_elapsed;
-	long long bytes_trim;
-	int io_trim;
+	long long bytes_trim = 0;
+	int io_trim = 0;
+	u64 bps_limit;
+	u32 iops_limit;
 
 	BUG_ON(time_before(tg->slice_end[rw], tg->slice_start[rw]));
 
@@ -758,11 +760,14 @@ static inline void throtl_trim_slice(struct throtl_grp *tg, bool rw)
 	if (!time_elapsed)
 		return;
 
-	bytes_trim = calculate_bytes_allowed(tg_bps_limit(tg, rw),
-					     time_elapsed) +
-		     tg->carryover_bytes[rw];
-	io_trim = calculate_io_allowed(tg_iops_limit(tg, rw), time_elapsed) +
-		  tg->carryover_ios[rw];
+	bps_limit = tg_bps_limit(tg, rw);
+	iops_limit = tg_iops_limit(tg, rw);
+	if (tg->bytes_disp[rw] > 0 && bps_limit != U64_MAX)
+		bytes_trim = calculate_bytes_allowed(bps_limit,
+			     time_elapsed) + tg->carryover_bytes[rw];
+	if (tg->io_disp[rw] > 0 && iops_limit != UINT_MAX)
+		io_trim = calculate_io_allowed(iops_limit, time_elapsed) +
+			  tg->carryover_ios[rw];
 	if (bytes_trim <= 0 && io_trim <= 0)
 		return;
 
-- 
2.39.2