linux-kernel - Re: [PATCH v3 2/2] blk-throttle: kill the no longer needed overflow check in calculate_bytes

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Message-ID: <20250818132103.GE18626@redhat.com>
Date: Mon, 18 Aug 2025 15:21:04 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: David Laight <david.laight.linux@...il.com>
Cc: Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Li RongQing <lirongqing@...du.com>, Yu Kuai <yukuai3@...wei.com>,
	Khazhismel Kumykov <khazhy@...omium.org>,
	Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org,
	x86@...nel.org
Subject: Re: [PATCH v3 2/2] blk-throttle: kill the no longer needed overflow
 check in calculate_bytes_allowed()

On 08/17, David Laight wrote:
>
> On Fri, 15 Aug 2025 18:41:02 +0200
> Oleg Nesterov <oleg@...hat.com> wrote:
>
> > Now that mul_u64_u64_div_u64() can't crash there is no need to check for
> > possible overflow in calculate_bytes_allowed().
> >
> > Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> > ---
> >  block/blk-throttle.c | 6 ------
> >  1 file changed, 6 deletions(-)
> >
> > diff --git a/block/blk-throttle.c b/block/blk-throttle.c
> > index 397b6a410f9e..66339e22cc85 100644
> > --- a/block/blk-throttle.c
> > +++ b/block/blk-throttle.c
> > @@ -601,12 +601,6 @@ static unsigned int calculate_io_allowed(u32 iops_limit,
> >
> >  static u64 calculate_bytes_allowed(u64 bps_limit, unsigned long jiffy_elapsed)
> >  {
> > -	/*
> > -	 * Can result be wider than 64 bits?
> > -	 * We check against 62, not 64, due to ilog2 truncation.
> > -	 */
> > -	if (ilog2(bps_limit) + ilog2(jiffy_elapsed) - ilog2(HZ) > 62)
> > -		return U64_MAX;
> >  	return mul_u64_u64_div_u64(bps_limit, (u64)jiffy_elapsed, (u64)HZ);
>
> Not directly related, but the two (u64) casts are pointless and can be removed.

Yeah... I only reverted 2dd710d476f2 ("blk-throttle: check for overflow in
calculate_bytes_allowed")

Oleg.