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io_uring's IORING_OP_TIMEOUT and IORING_OP_LINK_TIMEOUT accept a timespec from the caller via io_parse_user_time(). With IORING_TIMEOUT_ABS, the timestamp is an absolute deadline on the selected clock. The clock is CLOCK_MONOTONIC by default. CLOCK_BOOTTIME and CLOCK_REALTIME are also selectable. A submitter inside a CLONE_NEWTIME time namespace observes CLOCK_MONOTONIC and CLOCK_BOOTTIME shifted by the namespace's offsets relative to the host. Every other ABS timer interface in the kernel converts the caller's absolute time to host view via timens_ktime_to_host() before arming an hrtimer: kernel/time/posix-timers.c -- timer_settime(TIMER_ABSTIME) kernel/time/posix-stubs.c -- clock_nanosleep(TIMER_ABSTIME) kernel/time/alarmtimer.c -- alarm_timer_nsleep(TIMER_ABSTIME) fs/timerfd.c -- timerfd_settime(TFD_TIMER_ABSTIME) io_parse_user_time() does not. As a result, an absolute timeout submitted from within a time namespace is interpreted in host view. That is generally a different point in time. It may already be in the past, causing the timer to fire immediately, or far in the future, causing the timer not to fire when expected. Reproducer: in unshare --user --time, with a -10s monotonic offset, submit IORING_OP_TIMEOUT with IORING_TIMEOUT_ABS and deadline = now + 1s. The CQE is delivered after <1ms instead of the expected ~1s. Apply timens_ktime_to_host() to the parsed time when IORING_TIMEOUT_ABS is set. Split the existing clock id resolver in io_timeout_get_clock() into a flags only helper io_flags_to_clock(), so io_parse_user_time() can resolve the clock without a struct io_timeout_data. timens_ktime_to_host() is a no-op for clocks not affected by time namespaces, e.g. CLOCK_REALTIME. It is also a no-op for callers in the initial time namespace. The fast path is unchanged. SQPOLL is also covered. The SQPOLL kernel thread is created via create_io_thread() with CLONE_THREAD and no CLONE_NEW* flag. copy_namespaces() therefore shares the submitter's nsproxy by reference. Inside the SQPOLL kthread, current->nsproxy->time_ns is the submitter's time_ns. timens_ktime_to_host() resolves correctly. Suggested-by: Pavel Begunkov <asml.silence@gmail.com> Suggested-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: Maoyi Xie <maoyi.xie@ntu.edu.sg> Link: https://patch.msgid.link/20260504153755.1293932-2-maoyi.xie@ntu.edu.sg Signed-off-by: Jens Axboe <axboe@kernel.dk> |
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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