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Nikhil 7474f3a610 vduse: do not take dev->rwsem in the virtqueue kick path
vduse_vq_kick() runs in the context of the vdpa .kick_vq callback. With
the virtio_vdpa bus driver that callback is invoked by virtqueue_notify()
from the virtio device driver, which may be an atomic context: virtio-blk
kicks from ->queue_rq(), which blk-mq dispatches under rcu_read_lock()
(the tag set does not use BLK_MQ_F_BLOCKING), and virtio-net kicks from
its xmit path with the tx queue lock held.

Commit b282418bc3 ("vduse: Add suspend") made vduse_vq_kick() take
dev->rwsem for reading in order to check dev->suspended. down_read() may
sleep, so with CONFIG_DEBUG_ATOMIC_SLEEP the first I/O on a VDUSE-backed
virtio-blk device bound to virtio_vdpa now triggers:

  BUG: sleeping function called from invalid context at kernel/locking/rwsem.c:1573
  in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid: 27, name: kworker/1:0H
  preempt_count: 0, expected: 0
  RCU nest depth: 1, expected: 0
  3 locks held by kworker/1:0H/27:
   #0: ((wq_completion)kblockd){+.+.}-{0:0}, at: process_one_work+0xac7/0xcf0
   #1: ((work_completion)(&(&hctx->run_work)->work)){+.+.}-{0:0}, at: process_one_work+0x51f/0xcf0
   #2: (rcu_read_lock){....}-{1:3}, at: blk_mq_run_work_fn+0x119/0x220
  Workqueue: kblockd blk_mq_run_work_fn
  Call Trace:
   <TASK>
   dump_stack_lvl+0x80/0xa0
   __might_resched+0x231/0x370
   down_read+0x73/0x330
   vduse_vq_kick+0x30/0x120
   virtio_vdpa_notify+0x63/0x80
   virtqueue_notify+0x45/0x70
   virtio_queue_rq+0x19d/0x300
   blk_mq_dispatch_rq_list+0x269/0xe20
   __blk_mq_sched_dispatch_requests+0x761/0xa60
   blk_mq_sched_dispatch_requests+0x6b/0xc0
   blk_mq_run_work_fn+0x143/0x220
   process_one_work+0x581/0xcf0
   worker_thread+0x2fc/0x5a0
   kthread+0x1cc/0x210
   ret_from_fork+0x3c4/0x540
   ret_from_fork_asm+0x1a/0x30
   </TASK>

Without CONFIG_DEBUG_ATOMIC_SLEEP, a kick that finds the rwsem
write-locked by vduse_dev_reset() or vduse_vdpa_suspend() blocks inside
an RCU read-side critical section. The vhost_vdpa path kicks from the
vhost worker, i.e. process context, which is why this went unnoticed.

Check dev->suspended under vq->kick_lock instead, which the kick path
already takes, and have vduse_vdpa_suspend() cycle every virtqueue's
kick_lock after setting the flag. A kick that observed suspended == false
has thus finished signalling before suspend returns, which is the
guarantee the rwsem used to provide. The flag is now also read outside
the rwsem, so access it with READ_ONCE()/WRITE_ONCE().

Fixes: b282418bc3 ("vduse: Add suspend")
Signed-off-by: Nikhil <nikhilljatt@gmail.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Message-ID: <20260829225457.1037867-1-nikhilljatt@gmail.com>
2026-09-07 18:54:04 -04:00
arch bpf-fixes 2026-09-06 13:49:44 -07:00
block block: save page offset gaps in cloned bio 2026-09-01 08:42:34 -06:00
certs treewide: fix indentation and whitespace in Kconfig files 2026-05-28 21:24:42 -07:00
crypto This push fixes a memory allocation overrun in crypto acomp. 2026-08-28 09:28:40 -07:00
Documentation Miscellaneous IRQ subsystem fixes: 2026-09-06 10:35:24 -07:00
drivers vduse: do not take dev->rwsem in the virtqueue kick path 2026-09-07 18:54:04 -04:00
fs kmalloc_obj conversions for v7.3-rc2 2026-09-05 20:45:18 -07:00
include tracing fixes for v7.3: 2026-09-06 14:21:24 -07:00
init treewide: refresh kmalloc_obj() conversions 2026-09-04 21:37:00 -07:00
io_uring treewide: refresh kmalloc_obj() conversions 2026-09-04 21:37:00 -07:00
ipc mm.git review status for master..mm-nonmm-stable 2026-08-23 08:07:11 -07:00
kernel tracing fixes for v7.3: 2026-09-06 14:21:24 -07:00
lib treewide: refresh kmalloc_obj() conversions 2026-09-04 21:37:00 -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 treewide: refresh kmalloc_obj() conversions 2026-09-04 21:37:00 -07:00
net kmalloc_obj conversions for v7.3-rc2 2026-09-05 20:45:18 -07:00
rust rust: pci: reject IRQ vector indices that do not fit in u32 2026-09-01 18:21:01 +02:00
samples tracing fixes for v7.3: 2026-08-30 09:22:00 -07:00
scripts Coccinelle patches for Linux v7.3 2026-08-30 10:42:40 -07:00
security kmalloc_obj conversions for v7.3-rc2 2026-09-05 20:45:18 -07:00
sound treewide: refresh kmalloc_obj() conversions 2026-09-04 21:37:00 -07:00
tools bpf-fixes 2026-09-06 13:49:44 -07:00
usr usr: Correct a spelling by changing a letter 2026-08-05 14:51:58 +02:00
virt Arm: 2026-08-25 11:48:04 -07:00
.clang-format drm/bridge: rename drm_for_each_bridge_in_chain_scoped() to drm_for_each_bridge_in_chain() 2026-07-14 17:55:51 +02:00
.clippy.toml rust: bump Clippy's MSRV and clean incompatible_msrv allows 2026-04-07 09:51:39 +02:00
.cocciconfig
.editorconfig editorconfig: add rst extension 2026-01-26 19:07:09 -08:00
.get_maintainer.ignore .get_maintainer.ignore: add Nathan Chancellor 2026-08-03 21:10:12 -07:00
.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 7.3-rc2 2026-09-04 13:42:16 -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 Driver core fixes for 7.3-rc2 2026-09-05 11:59:05 -07:00
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 virtio: add Eugenio Pérez as Maintainer 2026-09-07 18:54:03 -04:00
Makefile Linux 7.3-rc2 2026-09-06 15:07:20 -07:00
README README: remove out of place emdashes 2026-07-15 10:51:29 -06:00

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