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Jamal Hadi Salim 1d856251a0 net/sched: act_mirred: fix loop detection
Fix a loop scenario of ethx:egress->ethx:egress

Example setup to reproduce:
tc qdisc add dev ethx root handle 1: drr
tc filter add dev ethx parent 1: protocol ip prio 1 matchall \
         action mirred egress redirect dev ethx

Now ping out of ethx and you get a deadlock:

[  116.892898][  T307] ============================================
[  116.893182][  T307] WARNING: possible recursive locking detected
[  116.893418][  T307] 6.18.0-rc6-01205-ge05021a829b8-dirty #204 Not tainted
[  116.893682][  T307] --------------------------------------------
[  116.893926][  T307] ping/307 is trying to acquire lock:
[  116.894133][  T307] ffff88800c122908 (&sch->root_lock_key){+...}-{3:3}, at: __dev_queue_xmit+0x2210/0x3b50
[  116.894517][  T307]
[  116.894517][  T307] but task is already holding lock:
[  116.894836][  T307] ffff88800c122908 (&sch->root_lock_key){+...}-{3:3}, at: __dev_queue_xmit+0x2210/0x3b50
[  116.895252][  T307]
[  116.895252][  T307] other info that might help us debug this:
[  116.895608][  T307]  Possible unsafe locking scenario:
[  116.895608][  T307]
[  116.895901][  T307]        CPU0
[  116.896057][  T307]        ----
[  116.896200][  T307]   lock(&sch->root_lock_key);
[  116.896392][  T307]   lock(&sch->root_lock_key);
[  116.896605][  T307]
[  116.896605][  T307]  *** DEADLOCK ***
[  116.896605][  T307]
[  116.896864][  T307]  May be due to missing lock nesting notation
[  116.896864][  T307]
[  116.897123][  T307] 6 locks held by ping/307:
[  116.897302][  T307]  #0: ffff88800b4b0250 (sk_lock-AF_INET){+.+.}-{0:0}, at: raw_sendmsg+0xb20/0x2cf0
[  116.897808][  T307]  #1: ffffffff88c839c0 (rcu_read_lock){....}-{1:3}, at: ip_output+0xa9/0x600
[  116.898138][  T307]  #2: ffffffff88c839c0 (rcu_read_lock){....}-{1:3}, at: ip_finish_output2+0x2c6/0x1ee0
[  116.898459][  T307]  #3: ffffffff88c83960 (rcu_read_lock_bh){....}-{1:3}, at: __dev_queue_xmit+0x200/0x3b50
[  116.898782][  T307]  #4: ffff88800c122908 (&sch->root_lock_key){+...}-{3:3}, at: __dev_queue_xmit+0x2210/0x3b50
[  116.899132][  T307]  #5: ffffffff88c83960 (rcu_read_lock_bh){....}-{1:3}, at: __dev_queue_xmit+0x200/0x3b50
[  116.899442][  T307]
[  116.899442][  T307] stack backtrace:
[  116.899667][  T307] CPU: 2 UID: 0 PID: 307 Comm: ping Not tainted 6.18.0-rc6-01205-ge05021a829b8-dirty #204 PREEMPT(voluntary)
[  116.899672][  T307] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[  116.899675][  T307] Call Trace:
[  116.899678][  T307]  <TASK>
[  116.899680][  T307]  dump_stack_lvl+0x6f/0xb0
[  116.899688][  T307]  print_deadlock_bug.cold+0xc0/0xdc
[  116.899695][  T307]  __lock_acquire+0x11f7/0x1be0
[  116.899704][  T307]  lock_acquire+0x162/0x300
[  116.899707][  T307]  ? __dev_queue_xmit+0x2210/0x3b50
[  116.899713][  T307]  ? srso_alias_return_thunk+0x5/0xfbef5
[  116.899717][  T307]  ? stack_trace_save+0x93/0xd0
[  116.899723][  T307]  _raw_spin_lock+0x30/0x40
[  116.899728][  T307]  ? __dev_queue_xmit+0x2210/0x3b50
[  116.899731][  T307]  __dev_queue_xmit+0x2210/0x3b50

Fixes: 178ca30889 ("Revert "net/sched: Fix mirred deadlock on device recursion"")
Tested-by: Victor Nogueira <victor@mojatatu.com>
Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
Link: https://patch.msgid.link/20251210162255.1057663-1-jhs@mojatatu.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
2025-12-18 16:42:18 +01:00
arch Networking changes for 6.19. 2025-12-03 17:24:33 -08:00
block vfs-6.19-rc1.inode 2025-12-01 09:02:34 -08:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto Networking changes for 6.19. 2025-12-03 17:24:33 -08:00
Documentation Networking changes for 6.19. 2025-12-03 17:24:33 -08:00
drivers net/mlx5e: Don't include PSP in the hard MTU calculations 2025-12-18 13:39:30 +01:00
fs Networking changes for 6.19. 2025-12-03 17:24:33 -08:00
include netfilter: nf_tables: avoid chain re-validation if possible 2025-12-15 15:02:44 +01:00
init Kbuild updates for v6.19 2025-12-03 14:42:21 -08:00
io_uring vfs-6.19-rc1.fd_prepare.fs 2025-12-01 17:32:07 -08:00
ipc vfs-6.19-rc1.fd_prepare.fs 2025-12-01 17:32:07 -08:00
kernel ynl: add regen hint to new headers 2025-12-08 23:52:43 -08:00
lib bpf-next-6.19 2025-12-03 16:54:54 -08:00
LICENSES LICENSES: Replace the obsolete address of the FSF in the GFDL-1.2 2025-07-24 11:15:39 +02:00
mm slab updates for 6.19 2025-12-03 11:53:47 -08:00
net net/sched: act_mirred: fix loop detection 2025-12-18 16:42:18 +01:00
rust Rust changes for v6.19 2025-12-03 14:16:49 -08:00
samples Networking changes for 6.19. 2025-12-03 17:24:33 -08:00
scripts Kbuild updates for v6.19 2025-12-03 14:42:21 -08:00
security This update includes the following changes: 2025-12-03 11:28:38 -08:00
sound ALSA: hda/realtek: Add quirk for HP ProBook 450 G8 2025-11-26 07:26:56 +01:00
tools selftests: netfilter: packetdrill: avoid failure on HZ=100 kernel 2025-12-15 15:04:04 +01:00
usr initramfs: add gen_init_cpio to hostprogs unconditionally 2025-11-26 21:55:40 +01:00
virt A large overhaul of the restartable sequences and CID management: 2025-12-02 08:48:53 -08:00
.clang-format memblock: drop for_each_free_mem_pfn_range_in_zone_from() 2025-09-14 08:49:03 +03:00
.clippy.toml rust: clean Rust 1.88.0's warning about clippy::disallowed_macros configuration 2025-05-07 00:11:47 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore MAINTAINERS: remove Alyssa Rosenzweig 2025-09-18 21:17:31 +02:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore rust: kbuild: add proc macro library support 2025-11-24 17:15:36 +01:00
.mailmap Kbuild updates for v6.19 2025-12-03 14:42:21 -08:00
.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 MAINTAINERS: Remove Jozsef Kadlecsik from MAINTAINERS file 2025-12-11 12:40:46 +01:00
Kbuild sched: Make migrate_{en,dis}able() inline 2025-09-25 09:57:16 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS MAINTAINERS: Remove Jozsef Kadlecsik from MAINTAINERS file 2025-12-11 12:40:46 +01:00
Makefile Kbuild updates for v6.19 2025-12-03 14:42:21 -08:00
README README: restructure with role-based documentation and guidelines 2025-11-29 08:40:33 -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


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



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