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Use rcu_assign_pointer to install TCP hijack offloads - #122
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* homa_hijack_init copies TCP's net_offload into hook_tcp_net_offload, patches gro_receive, then publishes it in inet_offloads with a plain store. Nothing orders the copy before the publish, so on a weakly ordered CPU (e.g. arm64) another CPU's GRO path could see the new pointer before the struct contents. rcu_assign_pointer adds the release barrier; same for inet6_offloads and for the restore in homa_hijack_end. * Also removes the four "cast adds address space '__rcu'" warnings from sparse (-Wsparse-all). Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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homa_hijack_init publishes the patched copy of TCP's net_offload into
inet_offloads/inet6_offloadswith a plain store, so on weakly ordered CPUs (arm64) a concurrent GRO path could observe the pointer before the struct copy.rcu_assign_pointersupplies the release ordering; the restore in homa_hijack_end uses it too. Unload is already safe (homa_offload_end → inet_del_offload → synchronize_net).Found with sparse
-Wsparse-all(4× "cast adds address space '__rcu'"); all four are gone.No test: memory-ordering change, not observable in the unit harness. Unit tests: 862/862 pass.
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