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Add a reconfig_tx_stall test that detects the possibility of a TX stall after ring reconfiguration. The key observation is that drivers using netif_tx_start_all_queues() are prone to experiencing a stall when reconfiguration completes compared to drivers using netif_tx_wake_all_queues(). start_all_queues only clears DRV_XOFF, while wake_all_queues also calls __netif_schedule() to kick the qdisc. Without the kick, qdisc backlog present at reconfig time can stay stuck until a new trigger is issued. The test caps the TX ring at 64 entries so it fills quickly, then installs FQ on a target TX queue and sends UDP packets with SO_TXTIME scheduled in the future. With napi_defer_hard_irqs slowing completions, the small ring can fill when FQ releases the burst, leaving requeued qdisc backlog with no FQ timer to rescue it. A subsequent ring reconfig must wake the queues to drain the backlog. Simply starting the queues can leave it stuck. Some drivers lack backpressure on the TX path and may not be able to build up the qdisc backlog the test relies on. In that case report an expected failure (xfail) instead of a hard failure. Testing on some of the existing drivers: Driver-A does not have the bug, Driver-B has the bug, Driver-C had the bug but it is fixed now. Driver-A: ./drivers/net/ring_reconfig.py -t reconfig_tx_stall TAP version 13 1..1 Sent 1024 SO_TXTIME packets (+100ms) Backlog before reconfig: 1176378 bytes ok 1 ring_reconfig.reconfig_tx_stall Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 Driver-B: TAP version 13 1..1 Sent 128 SO_TXTIME packets (+100ms) Sent 128 SO_TXTIME packets (+200ms) Backlog before reconfig: 148372 bytes Check| At ./drivers/net/ring_reconfig.py, line 397, in reconfig_tx_stall: Check| ksft_eq(0, backlog, Check failed 0 != 148372 qdisc backlog stuck on queue 1 after ring .... not ok 1 ring_reconfig.reconfig_tx_stall Totals: pass:0 fail:1 xfail:0 xpass:0 skip:0 error:0 Driver-C: TAP version 13 1..1 Sent 128 SO_TXTIME packets (+100ms) Backlog before reconfig: 192278 bytes ok 1 ring_reconfig.reconfig_tx_stall Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 Signed-off-by: Mohsin Bashir <hmohsin@meta.com> Link: https://patch.msgid.link/20260731021543.1058526-1-mohsin.bashr@gmail.com 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 * 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. 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