From: Tejun Heo <tj@kernel.org>
To: Alex Kazinsky <a.kazinsky@ideco.ru>
Cc: Josef Bacik <josef@toxicpanda.com>, Jens Axboe <axboe@kernel.dk>,
cgroups@vger.kernel.org, linux-block@vger.kernel.org,
linux-kernel@vger.kernel.org, lvc-project@linuxtesting.org,
stable@vger.kernel.org
Subject: Re: [PATCH] blk-iocost: Fix overflow in donation weight calculation
Date: Fri, 13 Nov 2026 09:08:07 -1000 [thread overview]
Message-ID: <0076998cf3693ad6d92b4bda775e5956@kernel.org> (raw)
In-Reply-To: <20261113110842.4189035-1-a.kazinsky@ideco.ru>
On Fri, Nov 13, 2026 at 03:08:40PM +0400, Alex Kazinsky wrote:
> hweight_after_donation() receives usage as u32, clamped to the range
> [1, WEIGHT_ONE]. Since WEIGHT_ONE is 1 << 16, multiplying it by usage
> equal to WEIGHT_ONE wraps the 32-bit unsigned result to zero before
> it is passed to div64_s64().
>
> This makes new_hwi zero, which is then clamped to 1, incorrectly
> reducing the cgroup's in-use weight to the minimum.
>
> Cast WEIGHT_ONE to s64 before multiplication to preserve the full
> product.
>
> Found by Linux Verification Center (linuxtesting.org) with SVACE static
> analysis tool.
>
> Fixes: f1de2439ec43 ("blk-iocost: revamp donation amount determination")
> Cc: stable@vger.kernel.org
> Signed-off-by: Alex Kazinsky <a.kazinsky@ideco.ru>
Acked-by: Tejun Heo <tj@kernel.org>
Thanks.
--
tejun
next prev parent reply other threads:[~2026-11-13 19:08 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-11-13 11:08 [PATCH] blk-iocost: Fix overflow in donation weight calculation Alex Kazinsky
2026-11-13 19:08 ` Tejun Heo [this message]
2026-11-13 22:02 ` Jens Axboe
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