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__reserve_metadata_snap() and __release_metadata_snap() modify the
superblock's held_root directly in the block_manager's buffer. If the
subsequent metadata commit fails, the held_root gets flushed to disk
through the abort_transaction path, resulting in inconsistent metadata.
Reproducer 1: __reserve_metadata_snap()
1. Create a 2 MiB metadata device and make the region after the 14th
block inaccessible, to trigger metadata commit failure in the
subsequent reserve_metadata_snap operation. The 14th block will be
the shadow destination for the index block.
dmsetup create tmeta --table "0 112 linear /dev/sdc 0
112 3984 error"
2. Create a 16 MiB thin-pool
dmsetup create tdata --table "0 32768 zero"
dd if=/dev/zero of=/dev/mapper/tmeta bs=4k count=1
dmsetup create tpool --table "0 32768 thin-pool /dev/mapper/tmeta \
/dev/mapper/tdata 128 0 1 skip_block_zeroing"
3. Take a metadata snapshot to trigger metadata commit failure and
transaction abort. However, the held_root is written to disk,
breaking metadata consistency.
dmsetup message tpool 0 "reserve_metadata_snap"
thin_check v1.2.2 result:
Bad reference count for metadata block 6. Expected 2, but space map contains 1.
Bad reference count for metadata block 7. Expected 2, but space map contains 1.
Bad reference count for metadata block 13. Expected 1, but space map contains 0.
Reproducer 2: __release_metadata_snap()
1. Create a 2 MiB metadata device and make the region after the 16th
block inaccessible, to trigger metadata commit failure in the
subsequent release_metadata_snap operation. The 16th block will be
the shadow destination for the index block.
dmsetup create tmeta --table "0 128 linear /dev/sdc 0
128 3968 error"
2. Create a 16 MiB thin-pool
dmsetup create tdata --table "0 32768 zero"
dd if=/dev/zero of=/dev/mapper/tmeta bs=4k count=1
dmsetup create tpool --table "0 32768 thin-pool /dev/mapper/tmeta \
/dev/mapper/tdata 128 0 1 skip_block_zeroing"
3. Reserve then release the metadata snapshot, to trigger metadata
commit failure and transaction abort. The held_root gets removed
from the on-disk superblock, causing inconsistent metadata.
dmsetup message tpool 0 "reserve_metadata_snap"
dmsetup message tpool 0 "release_metadata_snap"
thin_check v1.2.2 result:
Bad reference count for metadata block 6. Expected 1, but space map contains 2.
Bad reference count for metadata block 7. Expected 1, but space map contains 2.
1 metadata blocks have leaked.
Fix by deferring the held_root update to commit time.
Additionally, move the existing-snapshot check in __reserve_metadata_snap
before the shadow operation to avoid unnecessary work. In
__release_metadata_snap, clear pmd->held_root before btree deletion so
partial failure leaks blocks rather than leaving a stale reference, and
unlock the snapshot block before decrementing its refcount.
Fixes:
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|---|---|---|
| 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