linux-kernel - Re: [PATCH] blk-throttle: Calculate allowed value only when the throttle is enabled

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Message-ID: <20231005170413.GB32420@redhat.com>
Date:   Thu, 5 Oct 2023 19:04:14 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Li Nan <linan666@...weicloud.com>
Cc:     Khazhy Kumykov <khazhy@...omium.org>, tj@...nel.org,
        josef@...icpanda.com, axboe@...nel.dk, yukuai3@...wei.com,
        cgroups@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, yi.zhang@...wei.com,
        houtao1@...wei.com, yangerkun@...wei.com
Subject: Re: [PATCH] blk-throttle: Calculate allowed value only when the
 throttle is enabled

sorry, didn't notice this part before.

I am not a asm expert (to say at least;) but

On 10/05, Li Nan wrote:
>
> When (a * mul) overflows, a divide 0 error occurs in
> mul_u64_u64_div_u64().

Just in case... No, iirc it is divq which triggers #DE when the
result of division doesn't fit u64.

(a * mul) can't overflow, the result is 128-bit rax:rdx number.

Oleg.