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: <20250630081349.4c9d7976@kernel.org>
Date: Mon, 30 Jun 2025 08:13:49 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: "Chia-Yu Chang (Nokia)" <chia-yu.chang@...ia-bell-labs.com>
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

On Sun, 29 Jun 2025 22:49:24 +0000 Chia-Yu Chang (Nokia) wrote:
> > 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..  
> 
> 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.

Let me ask again - why do you use WRITE_ONCE() at all if 
the modification takes the qdisc lock? Which reader are
you afraid of racing with?