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Kaitao Cheng dec068de6d mm/vmalloc: honor GFP constraints in pcpu_get_vm_areas()
Patch series "mm/percpu: Fix possible NOFS/NOIO reclaim recursion", v4.

Commit 9a5b183941 ("mm, percpu: do not consider sleepable allocations
atomic") allowed GFP_NOFS and GFP_NOIO percpu allocations to use
pcpu_alloc_mutex and the chunk creation slow path.  This restored the
allocation capability that was lost when those constrained allocations
were treated as atomic, but it also makes the percpu slow path visible to
callers from constrained reclaim contexts.

There are two related problems.

First, the create and populate slow paths do not fully preserve the
caller's allocation constraints.  pcpu_alloc_noprof() derives pcpu_gfp
from the caller supplied GFP mask and passes it down to the percpu backing
page allocator.  However, chunk creation calls pcpu_get_vm_areas(), and
chunk population can allocate temporary metadata or vmalloc page tables
while mapping backing pages.  Those internal allocations can still use
GFP_KERNEL, so a caller using GFP_NOFS or GFP_NOIO can enter unconstrained
FS or IO reclaim while holding pcpu_alloc_mutex.

One possible case is blk-cgroup after commit 5d726c4dbe ("blk-cgroup:
fix possible deadlock while configuring policy").  blkg_conf_prep() now
serializes against blkcg_deactivate_policy() with q->blkcg_mutex, and
blkg_alloc() uses GFP_NOIO because queue freeze and IO reclaim
dependencies can otherwise deadlock.  If the percpu slow path loses that
GFP_NOIO context, direct reclaim or writeback can issue IO to a frozen
queue while q->blkcg_mutex is held.

Second, allowing sleepable GFP_NOFS/GFP_NOIO allocations to take
pcpu_alloc_mutex means that unconstrained backing allocations made under
the mutex can create an FS/IO reclaim dependency against a constrained
caller which already holds an FS or IO lock and then waits for
pcpu_alloc_mutex.

This series fixes those issues in three steps:

  - pass the caller supplied GFP mask into pcpu_get_vm_areas() and use it
    for vmalloc metadata and KASAN shadow allocations;
  - pass the GFP mask through the chunk population path, including the
    temporary pages array and vmalloc page table allocation scope;
  - restrict percpu backing allocations performed while holding
    pcpu_alloc_mutex to GFP_NOIO, so they cannot recurse into IO or FS
    reclaim.

This keeps sleepable GFP_NOFS/GFP_NOIO percpu allocations working, while
avoiding the reclaim recursion risks introduced by making those
allocations eligible for the mutex-protected slow path.


This patch (of 4):

pcpu_alloc_noprof() derives pcpu_gfp from the caller supplied GFP mask and
passes it down to the backing percpu allocator.  However, when the percpu
vmalloc allocator has to create a new chunk, pcpu_create_chunk() calls
pcpu_get_vm_areas() to allocate the corresponding vmalloc areas.

pcpu_get_vm_areas() currently performs its internal allocations with
GFP_KERNEL, including vmap area metadata, vm_struct metadata and KASAN
vmalloc shadow population.  This means that a caller which deliberately
uses GFP_NOFS or GFP_NOIO can still enter FS or IO reclaim while creating
the vmalloc areas for a new percpu chunk.

One possible case is blk-cgroup after commit 5d726c4dbe ("blk-cgroup:
fix possible deadlock while configuring policy").  blkg_conf_prep() now
serializes against blkcg_deactivate_policy() with q->blkcg_mutex, and
blkg_alloc() was changed to GFP_NOIO for that reason:

  CPU0: blkg_conf_prep()
    mutex_lock(q->blkcg_mutex)
    blkg_alloc(..., GFP_NOIO)
      alloc_percpu_gfp(..., GFP_NOIO)
        pcpu_alloc_noprof(..., GFP_NOIO)
	  pcpu_create_chunk(GFP_NOIO)
	    pcpu_get_vm_areas()
              -> if percpu chunks are exhausted, chunk create may do
                 internal GFP_KERNEL allocations
              -> direct reclaim / writeback can issue IO to this queue
              -> IO waits because the queue is frozen

  CPU1: blkcg_deactivate_policy()
    blk_mq_freeze_queue(q)
    mutex_lock(q->blkcg_mutex)
      -> waits for CPU0
    ... unfreeze only happens after q->blkcg_mutex is acquired/released

So the concern is that the caller deliberately uses GFP_NOIO because it
may hold a lock which can be acquired after queue freeze, but the percpu
slow path can temporarily lose that allocation context.

Pass the caller supplied GFP mask from pcpu_create_chunk() to
pcpu_get_vm_areas(), and use it for the internal vmalloc metadata and
KASAN shadow allocations.

Link: https://lore.kernel.org/20260618130414.96383-1-kaitao.cheng@linux.dev
Link: https://lore.kernel.org/20260618130414.96383-2-kaitao.cheng@linux.dev
Fixes: 9a5b183941 ("mm, percpu: do not consider sleepable allocations atomic")
Signed-off-by: Kaitao Cheng <chengkaitao@kylinos.cn>
Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: Shivam Kalra <shivamkalra98@zohomail.in>
Acked-by: Dennis Zhou <dennis@kernel.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Christoph Lameter <cl@gentwo.org>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Tejun Heo <tj@kernel.org>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2026-07-28 21:11:46 -07:00
arch m68knommu: fix on top off v7.2-rc4 2026-07-26 08:59:55 -07:00
block block: fix aligning of bounced dio read bios 2026-07-16 06:11:37 -06:00
certs treewide: fix indentation and whitespace in Kconfig files 2026-05-28 21:24:42 -07:00
crypto crypto: aes - Fix conditions for selecting MAC dependencies 2026-07-09 11:06:22 -04:00
Documentation spi: Fixes for v7.2 2026-07-26 12:13:42 -07:00
drivers Pin control fixes for the v7.2 series: 2026-07-27 08:48:48 -07:00
fs 13 hotfixes. All are cc:stable. 11 are for MM. All are singletons - 2026-07-27 14:36:26 -07:00
include mm/vmalloc: honor GFP constraints in pcpu_get_vm_areas() 2026-07-28 21:11:46 -07:00
init rust: allow suspicious_runtime_symbol_definitions lint for Rust >= 1.98 2026-06-29 13:02:15 +02:00
io_uring io_uring-7.2-20260724 2026-07-24 19:58:03 -07:00
ipc kernel-7.2-rc1.misc 2026-06-15 03:05:50 +05:30
kernel tracing fix for 7.2: 2026-07-26 09:15:59 -07:00
lib 13 hotfixes. All are cc:stable. 11 are for MM. All are singletons - 2026-07-27 14:36:26 -07:00
LICENSES LICENSES: Add modern form of the LGPL-2.1 tags to the usage guide section 2025-10-22 07:58:19 +02:00
mm mm/vmalloc: honor GFP constraints in pcpu_get_vm_areas() 2026-07-28 21:11:46 -07:00
net BPF fixes: 2026-07-24 19:31:12 -07:00
rust rust: time: fix as_micros_ceil() to round correctly for negative Delta 2026-07-18 19:07:35 +02:00
samples tracing fixes for 7.2: 2026-07-12 09:46:37 -07:00
scripts scripts/sorttable: Handle RISC-V patchable ftrace entries 2026-06-25 13:15:03 -06:00
security keys: make keyring key-chunk byte order agree with keyring_diff_objects() 2026-07-23 18:23:39 +03:00
sound ALSA: hda/realtek - Add quirk for Dell Pro QC1255 2026-07-21 09:55:17 +02:00
tools tools/mm: add thp_swap_allocator_test binary to .gitignore 2026-07-28 21:11:43 -07:00
usr kbuild: uapi: also test UAPI headers against C++ compilers 2026-03-25 13:24:42 +01:00
virt KVM/arm64 fixes for 7.2, take #2 2026-07-15 12:13:30 +02:00
.clang-format clang-format: fix formatting of guard() and scoped_guard() statements 2026-05-28 21:24:41 -07:00
.clippy.toml rust: bump Clippy's MSRV and clean incompatible_msrv allows 2026-04-07 09:51:39 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig editorconfig: add rst extension 2026-01-26 19:07:09 -08:00
.get_maintainer.ignore .get_maintainer.ignore: add myself 2026-04-02 16:48:25 +02:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore SPDX patches for 7.2-rc1 2026-06-22 12:06:22 -07:00
.mailmap drm fixes for 7.2-rc5 2026-07-24 14:11:53 -07:00
.pylintrc docs: Move the python libraries to tools/lib/python 2025-11-18 09:22:40 -07:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS CREDITS: Add Wolfram Sang 2026-07-14 16:34:04 +02:00
Kbuild checksyscalls: move instance functionality into generic code 2026-04-05 09:21:32 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS Changes since the last update: 2026-07-27 09:31:44 -07:00
Makefile Linux 7.2-rc5 2026-07-26 14:45:48 -07:00
README docs: add AI Coding Assistants documentation 2026-01-06 14:55:06 -07:00

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