mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
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Gerd Rausch
db69e9b838
RDS/TCP differs from RDS/RDMA in that message acknowledgment is done based on TCP sequence numbers: As soon as the last byte of a message has been acknowledged by the TCP stack of a peer, "rds_tcp_write_space()" goes on to discard prior messages from the send queue. Which is fine, for as long as the receiver never throws any messages away. Unfortunately, that is *not* the case since the introduction of MPRDS: commit1a0e100fb2"RDS: TCP: Enable multipath RDS for TCP" A new function "rds_tcp_accept_one_path" was introduced, which is entitled to return "NULL", if no connection path is currently available. Unfortunately, this happens after the "->accept()" call, and the new socket often already contains messages, since the peer already transitioned to "RDS_CONN_UP" on behalf of "TCP_ESTABLISHED". That's also the case after this [1]: commit1a0e100fb2"RDS: TCP: Force every connection to be initiated by numerically smaller IP address" which tried to address the situation of pending data by only transitioning connections from a smaller IP address to "RDS_CONN_UP". But even in those cases, and in particular if the "RDS_EXTHDR_NPATHS" handshake has not occurred yet, and therefore we're working with "c_npaths <= 1", "c_conn[0]" may be in a state distinct from "RDS_CONN_DOWN", and therefore all messages on the just accepted socket will be tossed away. This fix changes "rds_tcp_accept_one": * If connected from a peer with a larger IP address, the new socket will continue to get closed right away. With commit [1] above, there should not be any messages in the socket receive buffer, since the peer never transitioned to "RDS_CONN_UP". Therefore it should be okay to not make any efforts to dispatch the socket receive buffer. * If connected from a peer with a smaller IP address, we call "rds_tcp_accept_one_path" to find a free slot/"path". If found, business goes on as usual. If none was found, we save/stash the newly accepted socket into "rds_tcp_accepted_sock", in order to not lose any messages that may have arrived already. We then return from "rds_tcp_accept_one" with "-ENOBUFS". Later on, when a slot/"path" does become available again (e.g. state transitioned to "RDS_CONN_DOWN", or HS extension header was received with "c_npaths > 1") we call "rds_tcp_conn_slots_available" that simply re-issues a "rds_tcp_accept_one_path" worker-callback and picks up the new socket from "rds_tcp_accepted_sock", and thereby continuing where it left with "-ENOBUFS" last time. Since a new slot has become available, those messages won't be lost, since processing proceeds as if that slot had been available the first time around. Signed-off-by: Gerd Rausch <gerd.rausch@oracle.com> Signed-off-by: Jack Vogel <jack.vogel@oracle.com> Signed-off-by: Allison Henderson <allison.henderson@oracle.com> Link: https://patch.msgid.link/20260122055213.83608-3-achender@kernel.org Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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 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 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