All of lore.kernel.org
 help / color / mirror / Atom feed
From: Tejun Heo <tj@kernel.org>
To: cgel.zte@gmail.com
Cc: axboe@kernel.dk, cgroups@vger.kernel.org,
	linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
	zealci@zte.com.cn, deng.changcheng@zte.com.cn
Subject: Re: [PATCH v2] block: Use div64_ul instead of do_div
Date: Mon, 29 Nov 2021 08:19:17 -1000	[thread overview]
Message-ID: <YaUZpZYI71K66Zka@slm.duckdns.org> (raw)
In-Reply-To: <20211118034033.163550-1-deng.changcheng@zte.com.cn>

On Thu, Nov 18, 2021 at 03:40:33AM +0000, cgel.zte@gmail.com wrote:
> From: Changcheng Deng <deng.changcheng@zte.com.cn>
> 
> do_div() does a 64-by-32 division. Here the divisor is an unsigned long
> which on some platforms is 64 bit wide. So use div64_ul instead of do_div
> to avoid a possible truncation.
> 
> Reported-by: Zeal Robot <zealci@zte.com.cn>
> Signed-off-by: Changcheng Deng <deng.changcheng@zte.com.cn>
> ---
>  block/blk-throttle.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/block/blk-throttle.c b/block/blk-throttle.c
> index 39bb6e68a9a2..2db635d66617 100644
> --- a/block/blk-throttle.c
> +++ b/block/blk-throttle.c
> @@ -1903,7 +1903,7 @@ static void throtl_downgrade_check(struct throtl_grp *tg)
>  
>  	if (tg->bps[READ][LIMIT_LOW]) {
>  		bps = tg->last_bytes_disp[READ] * HZ;
> -		do_div(bps, elapsed_time);
> +		bps = div64_ul(bps, elapsed_time);

Yeah, the divisor is ulong for whatever reason but the thing is in jiffies.
I have a hard time imagining it overflowing 32bit. I'm not sure how useful
this patch is.

-- 
tejun

WARNING: multiple messages have this Message-ID (diff)
From: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
To: cgel.zte-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
Cc: axboe-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org,
	cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-block-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	zealci-Th6q7B73Y6EnDS1+zs4M5A@public.gmane.org,
	deng.changcheng-Th6q7B73Y6EnDS1+zs4M5A@public.gmane.org
Subject: Re: [PATCH v2] block: Use div64_ul instead of do_div
Date: Mon, 29 Nov 2021 08:19:17 -1000	[thread overview]
Message-ID: <YaUZpZYI71K66Zka@slm.duckdns.org> (raw)
In-Reply-To: <20211118034033.163550-1-deng.changcheng-Th6q7B73Y6EnDS1+zs4M5A@public.gmane.org>

On Thu, Nov 18, 2021 at 03:40:33AM +0000, cgel.zte-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org wrote:
> From: Changcheng Deng <deng.changcheng-Th6q7B73Y6EnDS1+zs4M5A@public.gmane.org>
> 
> do_div() does a 64-by-32 division. Here the divisor is an unsigned long
> which on some platforms is 64 bit wide. So use div64_ul instead of do_div
> to avoid a possible truncation.
> 
> Reported-by: Zeal Robot <zealci-Th6q7B73Y6EnDS1+zs4M5A@public.gmane.org>
> Signed-off-by: Changcheng Deng <deng.changcheng-Th6q7B73Y6EnDS1+zs4M5A@public.gmane.org>
> ---
>  block/blk-throttle.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/block/blk-throttle.c b/block/blk-throttle.c
> index 39bb6e68a9a2..2db635d66617 100644
> --- a/block/blk-throttle.c
> +++ b/block/blk-throttle.c
> @@ -1903,7 +1903,7 @@ static void throtl_downgrade_check(struct throtl_grp *tg)
>  
>  	if (tg->bps[READ][LIMIT_LOW]) {
>  		bps = tg->last_bytes_disp[READ] * HZ;
> -		do_div(bps, elapsed_time);
> +		bps = div64_ul(bps, elapsed_time);

Yeah, the divisor is ulong for whatever reason but the thing is in jiffies.
I have a hard time imagining it overflowing 32bit. I'm not sure how useful
this patch is.

-- 
tejun

  reply	other threads:[~2021-11-29 22:32 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-17  1:03 [PATCH] block: Use div64_ul instead of do_div cgel.zte
2021-11-18  3:40 ` [PATCH v2] " cgel.zte
2021-11-18  3:40   ` cgel.zte-Re5JQEeQqe8AvxtiuMwx3w
2021-11-29 18:19   ` Tejun Heo [this message]
2021-11-29 18:19     ` Tejun Heo
2021-12-02 16:50   ` Michal Koutný
2021-12-02 16:50     ` Michal Koutný

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=YaUZpZYI71K66Zka@slm.duckdns.org \
    --to=tj@kernel.org \
    --cc=axboe@kernel.dk \
    --cc=cgel.zte@gmail.com \
    --cc=cgroups@vger.kernel.org \
    --cc=deng.changcheng@zte.com.cn \
    --cc=linux-block@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=zealci@zte.com.cn \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.