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Tue, 10 Nov 2026 08:55:51 -0800 (PST) Received: from localhost ([2a03:2880:9ff:60::]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-3752060dc0csm9545342eec.14.2026.11.10.08.55.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 10 Nov 2026 08:55:50 -0800 (PST) Date: Tue, 10 Nov 2026 08:55:45 -0800 From: Stanislav Fomichev To: Jakub Kicinski Cc: davem@davemloft.net, netdev@vger.kernel.org, edumazet@google.com, pabeni@redhat.com, andrew+netdev@lunn.ch, horms@kernel.org, sdf@fomichev.me Subject: Re: [PATCH net-next] net: opt loopback into instance locking Message-ID: References: <20261109173902.1225585-1-kuba@kernel.org> X-Mailing-List: netdev@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20261109173902.1225585-1-kuba@kernel.org> On 11/09, Jakub Kicinski wrote: > netdev netlink iterates over devices when dumping queues/NAPIs/qstats > etc. and takes rtnl_lock or instance lock depending on the underlying > device. Currently even if all the "real" devices in the system are ops > locked we still have to take rtnl_lock for lo (only to find out > that it doesn't even have queues or NAPIs to report). > Opt loopback into having control path under the ops lock. > > This is a pretty obvious thing to do, I've held back this > patch because we used to only apply ops locking on physical devices. > netkit queue leasing made a precedent for (far more complex) > SW devices enabling ops locking. Now adding it to lo should > not create much new bug surface. > > I considered an alternative of adding a "predicate" to the iteration > primitive so that we can skip the devices which obviously don't > support given API (eg qstat) without any locking. But it's more > LoC and real_num_.x_queues is not currently WRITE_ONCE()ed so > it doesn't work too well for queues. > > Signed-off-by: Jakub Kicinski > --- > v3: > - pre-req commit b6f74dff6d26 ("net: use two lockdep classes for > the netdev instance lock") was merged > - no change Acked-by: Stanislav Fomichev