linux-kernel - [PATCH] block: iocost: ensure hweight

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Message-ID: <20241122072609.29429-1-daikunhai@didiglobal.com>
Date: Fri, 22 Nov 2024 15:26:09 +0800
From: Kunhai Dai <daikunhai@...iglobal.com>
To: <tj@...nel.org>, <josef@...icpanda.com>, <axboe@...nel.dk>
CC: <cgroups@...r.kernel.org>, <linux-block@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Kunhai Dai <daikunhai@...iglobal.com>
Subject: [PATCH] block: iocost: ensure hweight_inuse is at least 1

The hweight_inuse calculation in transfer_surpluses() could potentially
result in a value of 0, which would lead to division by zero errors in
subsequent calculations that use this value as a divisor.

Signed-off-by: Kunhai Dai <daikunhai@...iglobal.com>
---
 block/blk-iocost.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/block/blk-iocost.c b/block/blk-iocost.c
index 384aa15e8260..65cdb55d30cc 100644
--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c
@@ -1999,9 +1999,10 @@ static void transfer_surpluses(struct list_head *surpluses, struct ioc_now *now)
 		parent = iocg->ancestors[iocg->level - 1];
 
 		/* b' = gamma * b_f + b_t' */
-		iocg->hweight_inuse = DIV64_U64_ROUND_UP(
-			(u64)gamma * (iocg->hweight_active - iocg->hweight_donating),
-			WEIGHT_ONE) + iocg->hweight_after_donation;
+		iocg->hweight_inuse = max_t(u64, 1,
+			DIV64_U64_ROUND_UP(
+				(u64)gamma * (iocg->hweight_active - iocg->hweight_donating),
+				WEIGHT_ONE) + iocg->hweight_after_donation);
 
 		/* w' = s' * b' / b'_p */
 		inuse = DIV64_U64_ROUND_UP(
-- 
2.27.0