netdev - RE: [PATCH v20 net-next 1/6] sched: Struct definition and parsing of dualpi2 qdisc

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID:
 <PAXPR07MB79849FDC079A2ECB144D75D1A347A@PAXPR07MB7984.eurprd07.prod.outlook.com>
Date: Sun, 29 Jun 2025 22:49:24 +0000
From: "Chia-Yu Chang (Nokia)" <chia-yu.chang@...ia-bell-labs.com>
To: Jakub Kicinski <kuba@...nel.org>
CC: "alok.a.tiwari@...cle.com" <alok.a.tiwari@...cle.com>,
	"pctammela@...atatu.com" <pctammela@...atatu.com>, "horms@...nel.org"
	<horms@...nel.org>, "donald.hunter@...il.com" <donald.hunter@...il.com>,
	"xandfury@...il.com" <xandfury@...il.com>, "netdev@...r.kernel.org"
	<netdev@...r.kernel.org>, "dave.taht@...il.com" <dave.taht@...il.com>,
	"pabeni@...hat.com" <pabeni@...hat.com>, "jhs@...atatu.com"
	<jhs@...atatu.com>, "stephen@...workplumber.org"
	<stephen@...workplumber.org>, "xiyou.wangcong@...il.com"
	<xiyou.wangcong@...il.com>, "jiri@...nulli.us" <jiri@...nulli.us>,
	"davem@...emloft.net" <davem@...emloft.net>, "edumazet@...gle.com"
	<edumazet@...gle.com>, "andrew+netdev@...n.ch" <andrew+netdev@...n.ch>,
	"ast@...erby.net" <ast@...erby.net>, "liuhangbin@...il.com"
	<liuhangbin@...il.com>, "shuah@...nel.org" <shuah@...nel.org>,
	"linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
	"ij@...nel.org" <ij@...nel.org>, "ncardwell@...gle.com"
	<ncardwell@...gle.com>, "Koen De Schepper (Nokia)"
	<koen.de_schepper@...ia-bell-labs.com>, "g.white@...lelabs.com"
	<g.white@...lelabs.com>, "ingemar.s.johansson@...csson.com"
	<ingemar.s.johansson@...csson.com>, "mirja.kuehlewind@...csson.com"
	<mirja.kuehlewind@...csson.com>, "cheshire@...le.com" <cheshire@...le.com>,
	"rs.ietf@....at" <rs.ietf@....at>, "Jason_Livingood@...cast.com"
	<Jason_Livingood@...cast.com>, "vidhi_goel@...le.com" <vidhi_goel@...le.com>
Subject: RE: [PATCH v20 net-next 1/6] sched: Struct definition and parsing of
 dualpi2 qdisc

> -----Original Message-----
> From: Jakub Kicinski <kuba@...nel.org> 
> Sent: Saturday, June 28, 2025 1:25 AM
> To: Chia-Yu Chang (Nokia) <chia-yu.chang@...ia-bell-labs.com>
> Cc: alok.a.tiwari@...cle.com; pctammela@...atatu.com; horms@...nel.org; donald.hunter@...il.com; xandfury@...il.com; netdev@...r.kernel.org; dave.taht@...il.com; pabeni@...hat.com; jhs@...atatu.com; stephen@...workplumber.org; xiyou.wangcong@...il.com; jiri@...nulli.us; davem@...emloft.net; edumazet@...gle.com; andrew+netdev@...n.ch; ast@...erby.net; liuhangbin@...il.com; shuah@...nel.org; linux-kselftest@...r.kernel.org; ij@...nel.org; ncardwell@...gle.com; Koen De Schepper (Nokia) <koen.de_schepper@...ia-bell-labs.com>; g.white@...lelabs.com; ingemar.s.johansson@...csson.com; mirja.kuehlewind@...csson.com; cheshire@...le.com; rs.ietf@....at; Jason_Livingood@...cast.com; vidhi_goel@...le.com
> Subject: Re: [PATCH v20 net-next 1/6] sched: Struct definition and parsing of dualpi2 qdisc
> 
> 
> CAUTION: This is an external email. Please be very careful when clicking links or opening attachments. See the URL nok.it/ext for additional information.
> 
> 
> 
> On Sat, 21 Jun 2025 21:33:26 +0200 chia-yu.chang@...ia-bell-labs.com
> wrote:
[...]
> > +
> > +     if (tb[TCA_DUALPI2_STEP_THRESH]) {
> > +             u32 step_th = nla_get_u32(tb[TCA_DUALPI2_STEP_THRESH]);
> > +             bool step_pkt = 
> > + nla_get_flag(tb[TCA_DUALPI2_STEP_PACKETS]);
> > +
> > +             WRITE_ONCE(q->step_in_packets, step_pkt);
> > +             WRITE_ONCE(q->step_thresh,
> > +                        step_pkt ? step_th : convert_us_to_nsec(step_th));
> > +     }
> 
> I don't get the reason for all these WRITE_ONCE()s.
> You lock the qdisc to make modifications, right?
> And the block under which I'm responding is performing two dependent writes, one to ->step_in_packets and the other to ->step_thresh a change which is definitely not atomic..

Hi,

Thanks again for other comments again, and I will take actions in the next version.

As there is only one step marking in L-queue, so we still need two WRITE_ONCE even two attributes (one for threshold in packets and one in time) are used.

When applying the step marking, we need to know either the computation is based on the sojourn time or queue length.

Best regards,
Chia-Yu