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Kuniyuki Iwashima 72d3b9a4c2 udp_tunnel: Remove synchronize_rcu() in udp_tunnel_sock_release().
Commit 3cf7203ca6 ("net/tunnel: wait until all sk_user_data
reader finish before releasing the sock") added synchronize_rcu()
in udp_tunnel_sock_release().

This was intended to protect the fast path of a dying vxlan device
from dereferencing vxlan_sock->sock->sk after sock_orphan() has set
sock->sk to NULL.

However, vxlan does not need to access struct socket itself
in the fast path; it only reads struct sock, and struct socket
is only used for tunnel setup and teardown.

This applies to all other UDP tunnel users, and they have been
converted to access struct sock directly.

In addition, each device-specific struct used in their fast paths
is freed after one RCU grace period.  Since this occurs after
udp_tunnel_sock_release(), the struct is guaranteed to be freed
after struct udp_sock.

Therefore, synchronize_rcu() in udp_tunnel_sock_release() is
now redundant.

Let's remove it.

Tested:

A script creating/upping vxlan devices in 4000 netns runs 10x
faster with this change.  We can see the same improvement with
other UDP tunnel devices as well.

  $ cat vxlan.sh
  for i in `seq 1 40`
  do
      (for j in `seq 1 100` ; do
            unshare -n bash -c "ip link add vxlan0 type vxlan id 100 local 127.0.0.1 dstport 4789 && ip link set vxlan0 up";
       done) &
  done
  wait

With bpftrace, we can see vxlan_stop() is significantly faster.

  bpftrace -e '
  kprobe:vxlan_stop {
          @start[tid] = nsecs;
  }

  kretprobe:vxlan_stop /@start[tid]/ {
          @duration_us = hist((nsecs - @start[tid]) / 1000);
          delete(@start[tid]);
  }

  END {
          printf("\nExecution time of vxlan_stop (us):\n");
  }'

Before:

  # time ./vxlan.sh // without bpftrace
  real	0m50.615s
  user	0m8.171s
  sys	1m45.101s

  @duration_us:
  [4K, 8K)            1266 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@                   |
  [8K, 16K)           1957 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
  [16K, 32K)           764 |@@@@@@@@@@@@@@@@@@@@                                |
  [32K, 64K)             6 |                                                    |
  [64K, 128K)            4 |                                                    |
  [128K, 256K)           3 |                                                    |

After:

  # time ./vxlan.sh // without bpftrace
  real	0m5.247s
  user	0m7.956s
  sys	1m47.404s

  @duration_us:
  [16, 32)            3411 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
  [32, 64)             383 |@@@@@                                               |
  [64, 128)            107 |@                                                   |
  [128, 256)            79 |@                                                   |
  [256, 512)            16 |                                                    |
  [512, 1K)              2 |                                                    |
  [1K, 2K)               2 |                                                    |

Next step is to remove another synchronize_net() in vxlan_stop()
and variants in other devices.

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260502031401.3557229-16-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
2026-05-05 17:47:06 -07:00
arch KVM/arm64 fixes for 7.1, take #1 2026-04-27 04:24:34 -04:00
block block: only restrict bio allocation gfp mask asked to block 2026-04-21 11:42:12 -06:00
certs Clang build fixes for 7.1 2026-04-24 09:29:51 -07:00
crypto This push contains the following changes: 2026-04-21 08:06:43 -07:00
Documentation Documentation/tcp_ao: Document the supported MAC algorithms and lengths 2026-05-02 10:18:09 -07:00
drivers pfcp: Store struct sock in struct pfcp_dev. 2026-05-05 17:47:05 -07:00
fs \n 2026-04-27 16:45:39 -07:00
include amt: Store struct sock in struct amt_dev. 2026-05-05 17:47:05 -07:00
init memblock: updates for 7.0-rc1 2026-04-18 11:29:14 -07:00
io_uring net: add net_iov_init() and use it to initialize ->page_type 2026-04-29 16:40:08 -07:00
ipc Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
kernel tracing fixes for v7.1: 2026-04-29 22:21:44 -07:00
lib sched_ext: Fixes for v7.1-rc1 2026-04-28 16:26:11 -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 slab fix for 7.1 2026-04-24 09:39:03 -07:00
net udp_tunnel: Remove synchronize_rcu() in udp_tunnel_sock_release(). 2026-05-05 17:47:06 -07:00
rust Char/Misc/IIO/and others driver updates for 7.1-rc1 2026-04-24 13:23:50 -07:00
samples soc: drivers for 7.1 2026-04-16 20:34:34 -07:00
scripts First round of Kbuild fixes for 7.1 2026-04-25 17:04:15 -07:00
security + Cleanups 2026-04-24 09:22:21 -07:00
sound ALSA: hda/tas2781: Fix incorrect bit update for non-book-zero or book 0 pages >1 2026-04-29 07:51:17 +02:00
tools selftests: net: bridge: add MRC and QQIC field encoding tests 2026-05-04 19:09:42 -07:00
usr kbuild: uapi: also test UAPI headers against C++ compilers 2026-03-25 13:24:42 +01:00
virt Arm: 2026-04-17 07:18:03 -07:00
.clang-format Devicetree updates for v7.0: 2026-02-11 18:27:08 -08:00
.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 Askar 2026-04-15 02:15:02 -07:00
.gitattributes
.gitignore kbuild: rust: provide an option to inline C helpers into Rust 2026-03-30 02:03:52 +02:00
.mailmap Char/Misc/IIO/and others driver updates for 7.1-rc1 2026-04-24 13:23:50 -07:00
.pylintrc docs: Move the python libraries to tools/lib/python 2025-11-18 09:22:40 -07:00
.rustfmt.toml
COPYING
CREDITS Delete some obsolete networking code 2026-04-24 09:41:58 -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 MAINTAINERS: update the IPv4/IPv6 entry and add Ido Schimmel 2026-04-29 16:52:33 -07:00
Makefile Linux 7.1-rc1 2026-04-26 14:19:00 -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