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Commite9895609cb("wind ->s_roots via ->d_sib instead of ->d_hash") moved secondary roots from ->d_hash to ->d_sib. Secondary roots are now d_unhashed(), so __d_drop() returns without removing them from ->s_roots. Consequently, d_drop() in do_one_tree() no longer guarantees progress through the list. If a secondary root is still busy once do_one_tree() is done with it, its final dput() cannot evict it. The root remains ->s_roots.first and the loop selects it forever, holding ->s_umount for write and repeatedly reporting the same dentry. The root does not need a leaked reference of its own for that. Every child pins its parent (d_alloc() takes a reference on it) and umount_check() deliberately reports a busy descendant instead of complaining about its ancestors, so a single leaked dentry reference anywhere below a secondary root is enough. For filesystems that build ->s_root with d_obtain_root() - nfs, ceph, nilfs2 snapshot mounts - that is the entire tree. Beforee9895609cb, ___d_drop() special-cased IS_ROOT dentries and removed them from ->s_roots regardless of their refcount, so the d_drop() in do_one_tree() detached the root from the superblock no matter what. Commit9c8c10e262("more graceful recovery in umount_collect()") deliberately made busy dentries nonfatal: report them and finish the unmount rather than BUG() while holding ->s_umount. Restore that by detaching the root in do_one_tree() itself, next to the d_drop() that used to do it. That covers both callers - the ->s_roots loop and ->s_root, which for the filesystems above is a secondary root as well. In the normal case dentry_unlist() finds ->d_sib already unhashed when eviction occurs. A permanently leaked reference remains leaked after unmount, as it did before e9895609cb7f; if the extra reference is merely delayed, its final dput() may run after teardown has advanced. Leaving the root on ->s_roots is not an alternative: the superblock would then be freed with a live dentry still linked into it, and that dentry's dentry_unlist() would take ->s_roots_lock on freed memory. Christian Brauner <brauner@kernel.org> says: Moved the ->s_roots removal from the shrink_dcache_for_umount() loop into do_one_tree(), so a busy ->s_root obtained from d_obtain_root() is detached on the first pass instead of being reported a second time when the loop picks it off ->s_roots. Extended the commit message with the pinned-ancestor case. Fixes:e9895609cb("wind ->s_roots via ->d_sib instead of ->d_hash") Signed-off-by: Karl Mehltretter <kmehltretter@gmail.com> Link: https://patch.msgid.link/20260729005933.15858-1-kmehltretter@gmail.com Signed-off-by: Christian Brauner (Amutable) <brauner@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. 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