mirror of
https://github.com/torvalds/linux.git
synced 2026-07-28 01:55:51 +02:00
Linux kernel source tree
Writing 0 to BFQ's low_latency attribute ends weight raising for active,
idle and async queues. The async cgroup path walks q->blkg_list, converts
each blkg to BFQ policy data and then reads bfqg->async_bfqq and
bfqg->async_idle_bfqq.
That walk was protected only by bfqd->lock. blkcg release work is
serialized by q->blkcg_mutex and q->queue_lock instead, and
blkg_free_workfn() can call BFQ's pd_free_fn before it removes
blkg->q_node from q->blkg_list. A low_latency reset can therefore still
find the blkg on the queue list after the BFQ policy data has been freed.
The buggy scenario involves two paths, with each column showing the order
within that path:
BFQ low_latency reset: blkcg blkg release work:
1. bfq_low_latency_store() 1. blkg_free_workfn() takes
calls bfq_end_wr(). q->blkcg_mutex.
2. bfq_end_wr_async() walks 2. BFQ pd_free_fn drops the
q->blkg_list. final bfq_group reference.
3. blkg_to_bfqg() returns 3. blkg->q_node remains on
the stale policy data. q->blkg_list until list_del_init().
4. bfq_end_wr_async_queues()
reads async queue fields.
Fix this by taking q->blkcg_mutex and q->queue_lock around the
q->blkg_list walk, then taking bfqd->lock before touching BFQ async
queues. The mutex serializes against policy-data free and queue_lock
stabilizes the list. Move the async reset out of bfq_end_wr()'s existing
bfqd->lock critical section so the lock order matches blkcg policy
callbacks.
Validation reproduced this kernel report:
BUG: KASAN: slab-use-after-free in bfq_end_wr_async_queues+0x246/0x340
Call Trace:
<TASK>
dump_stack_lvl+0x66/0xa0
print_report+0xce/0x630
? bfq_end_wr_async_queues+0x246/0x340
? srso_alias_return_thunk+0x5/0xfbef5
? __virt_addr_valid+0x20d/0x410
? bfq_end_wr_async_queues+0x246/0x340
kasan_report+0xe0/0x110
? bfq_end_wr_async_queues+0x246/0x340
bfq_end_wr_async_queues+0x246/0x340
bfq_end_wr_async+0xba/0x180
bfq_low_latency_store+0x4e5/0x690
? 0xffffffffc02150da
? __pfx_bfq_low_latency_store+0x10/0x10
? __pfx_bfq_low_latency_store+0x10/0x10
elv_attr_store+0xc4/0x110
kernfs_fop_write_iter+0x2f5/0x4a0
vfs_write+0x604/0x11f0
? __pfx_locks_remove_posix+0x10/0x10
? __pfx_vfs_write+0x10/0x10
ksys_write+0xf9/0x1d0
? __pfx_ksys_write+0x10/0x10
do_syscall_64+0x115/0x6a0
entry_SYSCALL_64_after_hwframe+0x77/0x7f
Allocated by task 544:
kasan_save_stack+0x33/0x60
kasan_save_track+0x14/0x30
__kasan_kmalloc+0xaa/0xb0
bfq_pd_alloc+0xc0/0x1b0
blkg_alloc+0x346/0x960
blkg_create+0x8c2/0x10d0
bio_associate_blkg_from_css+0x9f3/0xfa0
bio_associate_blkg+0xd9/0x200
bio_init+0x303/0x640
__blkdev_direct_IO_simple+0x56b/0x8a0
blkdev_direct_IO+0x8e7/0x2580
blkdev_read_iter+0x205/0x400
vfs_read+0x7b0/0xda0
ksys_read+0xf9/0x1d0
do_syscall_64+0x115/0x6a0
entry_SYSCALL_64_after_hwframe+0x77/0x7f
Freed by task 465:
kasan_save_stack+0x33/0x60
kasan_save_track+0x14/0x30
kasan_save_free_info+0x3b/0x60
__kasan_slab_free+0x5f/0x80
kfree+0x307/0x580
blkg_free_workfn+0xef/0x460
process_one_work+0x8d0/0x1870
worker_thread+0x575/0xf80
kthread+0x2e7/0x3c0
ret_from_fork+0x576/0x810
ret_from_fork_asm+0x1a/0x30
Fixes:
|
||
|---|---|---|
| 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