mirror of
https://github.com/torvalds/linux.git
synced 2026-07-27 09:36:22 +02:00
Linux kernel source tree
658eb69654
Currently sk_rethink_txhash() re-rolls the socket's txhash on RTO, PLB, and spurious-retransmission events, but the cached route is reused and the new hash is not propagated into the ECMP path selection logic. Two changes are needed to make rehash select a different local ECMP path: 1. Add __sk_dst_reset() alongside sk_rethink_txhash() in tcp_write_timeout(), tcp_rcv_spurious_retrans(), and tcp_plb_check_rehash() so the cached dst is invalidated and the next transmit triggers a fresh route lookup. 2. Set fl6->mp_hash from sk_txhash (or tcp_rsk(req)->txhash for SYN/ACK retransmits and syncookies) in tcp_v6_connect(), inet6_sk_rebuild_header(), inet6_csk_route_req(), inet6_csk_route_socket(), tcp_v6_send_response(), and cookie_v6_check() so fib6_select_path() picks a path based on the new hash. The mp_hash override only applies to fib_multipath_hash_policy 0 (the default L3 policy). Its hash includes the flow label, but that is 0 by default -- np->flow_label is unset, and auto_flowlabels only computes the on-wire label later, per packet -- so flows to the same peer share one local path. Keying the hash on sk_txhash makes the local path per-connection and lets a rehash re-select it. Policies 1-3 are left unchanged. The mp_hash assignment is factored into a small helper, ip6_ecmp_set_mp_hash(), shared by inet6_csk_route_req(), inet6_csk_route_socket(), tcp_v6_connect(), inet6_sk_rebuild_header(), tcp_v6_send_response(), and cookie_v6_check(). It applies (txhash >> 1) ?: 1 for policy 0 (the >> 1 keeps mp_hash in the 31-bit range; ?: 1 keeps it non-zero, since 0 would fall back to rt6_multipath_hash()). inet6_csk_route_socket() calls it only for sk_protocol == IPPROTO_TCP so that non-TCP callers (e.g., L2TP via inet6_csk_xmit) fall through to rt6_multipath_hash() and retain their existing flow-key-based ECMP behavior. tcp_v6_send_response() also sets mp_hash from the response txhash so that a control packet (a RST from the full socket, or an ACK from a time-wait socket) selects the same local ECMP nexthop as the connection's txhash rather than falling back to the flow hash. The time-wait socket's tw_txhash is copied from sk_txhash when the connection enters TIME_WAIT, so it reflects any rehash that occurred. Setting mp_hash explicitly is necessary because the default ECMP hash derives from fl6->flowlabel via np->flow_label, which is not updated from sk_txhash (REPFLOW is off by default). ip6_make_flowlabel() cannot help either, as it runs after the route lookup. As a consequence, for policy 0 the local ECMP path of an IPv6 TCP flow follows sk_txhash even when fl6->flowlabel is non-zero, e.g. a reflected (REPFLOW) or explicitly set (IPV6_FLOWLABEL_MGR) flow label. This is intentional: only local path selection changes, so rehash can recover from a failed path; the on-wire flow label is unchanged. sk_set_txhash() is moved before ip6_dst_lookup_flow() in tcp_v6_connect() so the initial ECMP path is selected by the same txhash that subsequent route rebuilds will use. This avoids unintended path changes when the cached dst is naturally invalidated (e.g., by PMTU discovery or route changes). The rehash sites (tcp_write_timeout(), tcp_plb_check_rehash(), and tcp_rcv_spurious_retrans()) call __sk_rethink_txhash_reset_dst(), which re-rolls the txhash and, when it changed, drops the cached dst so the next transmit re-runs route selection. The dst reset is guarded by sk->sk_family == AF_INET6 since IPv4 ECMP does not currently use sk_txhash for path selection. For IPv4-mapped IPv6 sockets this produces a redundant dst reset on a cold path (RTO/PLB); the subsequent IPv4 route lookup returns the same result. The helper is deliberately separate from sk_rethink_txhash() itself: dst_negative_advice() calls sk_rethink_txhash() before its own dst op, so resetting the dst inside sk_rethink_txhash() would skip that op (e.g. rt6_remove_exception_rt()). For syncookies, cookie_init_sequence() computes the cookie value before route_req() and sets txhash so the SYN-ACK selects the same ECMP path that cookie_v6_check() will use when the full socket is created. cookie_tcp_reqsk_init() derives txhash from the cookie so the full socket's ECMP path matches the SYN-ACK. Both the SYN-ACK assignment in tcp_conn_request() and the full-socket assignment in cookie_tcp_reqsk_init() set txhash from the cookie for IPv4 and IPv6 alike. On IPv6 this drives ECMP path selection; on IPv4, which does not use sk_txhash for ECMP, it only affects TX-queue selection. That selection scales the hash by its high bits (reciprocal_scale()), which are uniform in the keyed secure_tcp_syn_cookie() output -- the MSS index only perturbs the low bits -- so the queue distribution matches net_tx_rndhash(). cookie_init_sequence() is split from the former version that also called tcp_synq_overflow() and incremented SYNCOOKIESSENT; those side effects are now in cookie_record_sent(), called after route_req() succeeds so they are not bumped when route_req() fails. cookie_record_sent() is guarded by CONFIG_SYN_COOKIES to match the guard on tcp_synq_overflow(). route_req() receives 0 as tw_isn for the syncookie path so that tcp_v6_init_req() still saves ireq->pktopts for REPFLOW flowlabel reflection and IPv6 cmsg options. The ecn_ok clear for syncookies without timestamps stays after tcp_ecn_create_request() so it takes precedence. Signed-off-by: Neil Spring <ntspring@meta.com> Reviewed-by: Eric Dumazet <edumazet@google.com> Link: https://patch.msgid.link/20260615042158.1600746-2-ntspring@meta.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> |
||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .clippy.toml | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .pylintrc | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel ============ The Linux kernel is the core of any Linux operating system. It manages hardware, system resources, and provides the fundamental services for all other software. Quick Start ----------- * Report a bug: See Documentation/admin-guide/reporting-issues.rst * Get the latest kernel: https://kernel.org * Build the kernel: See Documentation/admin-guide/quickly-build-trimmed-linux.rst * Join the community: https://lore.kernel.org/ Essential Documentation ----------------------- All users should be familiar with: * Building requirements: Documentation/process/changes.rst * Code of Conduct: Documentation/process/code-of-conduct.rst * License: See COPYING Documentation can be built with make htmldocs or viewed online at: https://www.kernel.org/doc/html/latest/ Who Are You? ============ Find your role below: * New Kernel Developer - Getting started with kernel development * Academic Researcher - Studying kernel internals and architecture * Security Expert - Hardening and vulnerability analysis * Backport/Maintenance Engineer - Maintaining stable kernels * System Administrator - Configuring and troubleshooting * Maintainer - Leading subsystems and reviewing patches * Hardware Vendor - Writing drivers for new hardware * Distribution Maintainer - Packaging kernels for distros * AI Coding Assistant - LLMs and AI-powered development tools For Specific Users ================== New Kernel Developer -------------------- Welcome! Start your kernel development journey here: * Getting Started: Documentation/process/development-process.rst * Your First Patch: Documentation/process/submitting-patches.rst * Coding Style: Documentation/process/coding-style.rst * Build System: Documentation/kbuild/index.rst * Development Tools: Documentation/dev-tools/index.rst * Kernel Hacking Guide: Documentation/kernel-hacking/hacking.rst * Core APIs: Documentation/core-api/index.rst Academic Researcher ------------------- Explore the kernel's architecture and internals: * Researcher Guidelines: Documentation/process/researcher-guidelines.rst * Memory Management: Documentation/mm/index.rst * Scheduler: Documentation/scheduler/index.rst * Networking Stack: Documentation/networking/index.rst * Filesystems: Documentation/filesystems/index.rst * RCU (Read-Copy Update): Documentation/RCU/index.rst * Locking Primitives: Documentation/locking/index.rst * Power Management: Documentation/power/index.rst Security Expert --------------- Security documentation and hardening guides: * Security Documentation: Documentation/security/index.rst * LSM Development: Documentation/security/lsm-development.rst * Self Protection: Documentation/security/self-protection.rst * Reporting Vulnerabilities: Documentation/process/security-bugs.rst * CVE Procedures: Documentation/process/cve.rst * Embargoed Hardware Issues: Documentation/process/embargoed-hardware-issues.rst * Security Features: Documentation/userspace-api/seccomp_filter.rst Backport/Maintenance Engineer ----------------------------- Maintain and stabilize kernel versions: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * Backporting Guide: Documentation/process/backporting.rst * Applying Patches: Documentation/process/applying-patches.rst * Subsystem Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git for Maintainers: Documentation/maintainer/configure-git.rst System Administrator -------------------- Configure, tune, and troubleshoot Linux systems: * Admin Guide: Documentation/admin-guide/index.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Sysctl Tuning: Documentation/admin-guide/sysctl/index.rst * Tracing/Debugging: Documentation/trace/index.rst * Performance Security: Documentation/admin-guide/perf-security.rst * Hardware Monitoring: Documentation/hwmon/index.rst Maintainer ---------- Lead kernel subsystems and manage contributions: * Maintainer Handbook: Documentation/maintainer/index.rst * Pull Requests: Documentation/maintainer/pull-requests.rst * Managing Patches: Documentation/maintainer/modifying-patches.rst * Rebasing and Merging: Documentation/maintainer/rebasing-and-merging.rst * Development Process: Documentation/process/maintainer-handbooks.rst * Maintainer Entry Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git Configuration: Documentation/maintainer/configure-git.rst Hardware Vendor --------------- Write drivers and support new hardware: * Driver API Guide: Documentation/driver-api/index.rst * Driver Model: Documentation/driver-api/driver-model/driver.rst * Device Drivers: Documentation/driver-api/infrastructure.rst * Bus Types: Documentation/driver-api/driver-model/bus.rst * Device Tree Bindings: Documentation/devicetree/bindings/ * Power Management: Documentation/driver-api/pm/index.rst * DMA API: Documentation/core-api/dma-api.rst Distribution Maintainer ----------------------- Package and distribute the kernel: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * ABI Documentation: Documentation/ABI/README * Kernel Configuration: Documentation/kbuild/kconfig.rst * Module Signing: Documentation/admin-guide/module-signing.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Tainted Kernels: Documentation/admin-guide/tainted-kernels.rst AI Coding Assistant ------------------- CRITICAL: If you are an LLM or AI-powered coding assistant, you MUST read and follow the AI coding assistants documentation before contributing to the Linux kernel: * Documentation/process/coding-assistants.rst This documentation contains essential requirements about licensing, attribution, and the Developer Certificate of Origin that all AI tools must comply with. Communication and Support ========================= * Mailing Lists: https://lore.kernel.org/ * IRC: #kernelnewbies on irc.oftc.net * Bugzilla: https://bugzilla.kernel.org/ * MAINTAINERS file: Lists subsystem maintainers and mailing lists * Email Clients: Documentation/process/email-clients.rst