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AJvYcCXKDAViFdhtgIZylCl9LX3Y5PX7s6Idq3bsrz8tV1ba6Dig0eq2c6FLlETQJh8qbxGqjjCh7dzAARiScSR7LhVc1xlMLViAmHFnQCyFeHHOOcTkLxBklAHibNugAEJlfLy8 X-Gm-Message-State: AOJu0YwkeVE7RJMU06qy+w7tVhBhbUCRSUABloAjlEG5MIRidGjIoWu4 ppKp3ttNO7bK1J2f8OH+DGbAgnMwCaqAYxKmy4k5hSggdxQiz7DX2efkei8jCHRb/zAvDYJAUaS WmRJiJihwTfcd7zB2MArWTwf8J1c= X-Google-Smtp-Source: AGHT+IH/FR830JT8pwRZd0wvBGtIkpZow1qP+kLmcCEVpk9fkEEa5/VxH+ePDVFzg1KiUDBxgT+/5lAjf9QXwxtlq74= X-Received: by 2002:a17:906:3e07:b0:a46:8d30:b91c with SMTP id k7-20020a1709063e0700b00a468d30b91cmr2436519eji.34.1710902541936; Tue, 19 Mar 2024 19:42:21 -0700 (PDT) Precedence: bulk X-Mailing-List: lvs-devel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <5fde8ace-a0ac-4870-a7fe-ec2a24697112@gmail.com> In-Reply-To: <5fde8ace-a0ac-4870-a7fe-ec2a24697112@gmail.com> From: Jason Xing Date: Wed, 20 Mar 2024 10:41:44 +0800 Message-ID: Subject: Re: [net] Question about ipvs->sysctl_sync_threshold and READ_ONCE To: Zijie Zhao Cc: horms@verge.net.au, ja@ssi.bg, davem@davemloft.net, dsahern@kernel.org, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, netdev@vger.kernel.org, lvs-devel@vger.kernel.org, chenyuan0y@gmail.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, Mar 20, 2024 at 6:49=E2=80=AFAM Zijie Zhao wrot= e: > > Dear IPVS maintainers, > > We encountered an unusual usage of sysctl parameter while analyzing > kernel source code. > > > In include/net/ip_vs.h, line 1062 - 1070: > > ``` > static inline int sysctl_sync_threshold(struct netns_ipvs *ipvs) > { > return ipvs->sysctl_sync_threshold[0]; > } > > static inline int sysctl_sync_period(struct netns_ipvs *ipvs) > { > return READ_ONCE(ipvs->sysctl_sync_threshold[1]); > } > ``` > > Here, sysctl_sync_threshold[1] is accessed behind `READ_ONCE`, but > sysctl_sync_threshold[0] is not. Should sysctl_sync_threshold[0] also be > guarded by `READ_ONCE`? I'm not so sure and clear about the detailed history. AFAIK, readers accessing this sysctl knob (sysctl_sync_threshold) should be protected by READ_ONCE() because it can be changed concurrently. Probably the commit 749c42b620a95 missed this point many years ago and then commit 6aa7de059173a followed that. Thanks, Jason > > Please kindly let us know if we missed any key information and this is > actually intended. We appreciate your information and time! Thanks! > > > Links to the code: > https://elixir.bootlin.com/linux/v6.8.1/source/include/net/ip_vs.h#L1064 > https://elixir.bootlin.com/linux/v6.8.1/source/include/net/ip_vs.h#L1069 > > Best, > Zijie >