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Joel Fernandes 1cfa244f71 rcu: Fix rcu_read_unlock() deadloop due to IRQ work [ Upstream commit `b41642c877` ] During rcu_read_unlock_special(), if this happens during irq_exit(), we can lockup if an IPI is issued. This is because the IPI itself triggers the irq_exit() path causing a recursive lock up. This is precisely what Xiongfeng found when invoking a BPF program on the trace_tick_stop() tracepoint As shown in the trace below. Fix by managing the irq_work state correctly. irq_exit() __irq_exit_rcu() /* in_hardirq() returns false after this / preempt_count_sub(HARDIRQ_OFFSET) tick_irq_exit() tick_nohz_irq_exit() tick_nohz_stop_sched_tick() trace_tick_stop() / a bpf prog is hooked on this trace point / __bpf_trace_tick_stop() bpf_trace_run2() rcu_read_unlock_special() / will send a IPI to itself */ irq_work_queue_on(&rdp->defer_qs_iw, rdp->cpu); A simple reproducer can also be obtained by doing the following in tick_irq_exit(). It will hang on boot without the patch: static inline void tick_irq_exit(void) { + rcu_read_lock(); + WRITE_ONCE(current->rcu_read_unlock_special.b.need_qs, true); + rcu_read_unlock(); + Reported-by: Xiongfeng Wang <wangxiongfeng2@huawei.com> Closes: https://lore.kernel.org/all/9acd5f9f-6732-7701-6880-4b51190aa070@huawei.com/ Tested-by: Qi Xi <xiqi2@huawei.com> Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com> Reviewed-by: "Paul E. McKenney" <paulmck@kernel.org> Reported-by: Linux Kernel Functional Testing <lkft@linaro.org> [neeraj: Apply Frederic's suggested fix for PREEMPT_RT] Signed-off-by: Neeraj Upadhyay (AMD) <neeraj.upadhyay@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org>		History 2025-08-20 18:30:39 +02:00
arch	arm64: stacktrace: Check kretprobe_find_ret_addr() return value	2025-08-20 18:30:36 +02:00
block	block: ensure discard_granularity is zero when discard is not supported	2025-08-15 12:14:05 +02:00
certs	sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3	2024-09-20 19:52:48 +03:00
crypto	crypto: ecdsa - Harden against integer overflows in DIV_ROUND_UP()	2025-07-17 18:37:24 +02:00
Documentation	Documentation: ACPI: Fix parent device references	2025-08-20 18:30:15 +02:00
drivers	drm/ttm: Respect the shrinker core free target	2025-08-20 18:30:39 +02:00
fs	tracefs: Add d_delete to remove negative dentries	2025-08-20 18:30:21 +02:00
include	uapi: in6: restore visibility of most IPv6 socket options	2025-08-20 18:30:39 +02:00
init	io_uring: fix breakage in EXPERT menu	2025-08-15 12:13:32 +02:00
io_uring	io_uring/poll: fix POLLERR handling	2025-07-24 08:56:23 +02:00
ipc	ipc: fix to protect IPCS lookups using RCU	2025-06-27 11:11:22 +01:00
kernel	rcu: Fix rcu_read_unlock() deadloop due to IRQ work	2025-08-20 18:30:39 +02:00
lib	lib/alloc_tag: do not acquire non-existent lock in alloc_tag_top_users()	2025-07-17 18:37:14 +02:00
LICENSES	LICENSES: add 0BSD license text	2024-09-01 20:43:24 -07:00
mm	mm: swap: fix potential buffer overflow in setup_clusters()	2025-08-15 12:14:14 +02:00
net	net: ncsi: Fix buffer overflow in fetching version id	2025-08-20 18:30:38 +02:00
rust	rust: use `#[used(compiler)]` to fix build and `modpost` with Rust >= 1.89.0	2025-07-24 08:56:37 +02:00
samples	samples: mei: Fix building on musl libc	2025-08-15 12:13:38 +02:00
scripts	kconfig: qconf: fix ConfigList::updateListAllforAll()	2025-08-15 12:14:03 +02:00
security	securityfs: don't pin dentries twice, once is enough...	2025-08-20 18:30:21 +02:00
sound	ASoC: qcom: use drvdata instead of component to keep id	2025-08-20 18:30:28 +02:00
tools	selftests/bpf: Fix a user_ringbuf failure with arm64 64KB page size	2025-08-20 18:30:39 +02:00
usr	kbuild: hdrcheck: fix cross build with clang	2025-03-13 13:02:18 +01:00
virt	KVM: Allow CPU to reschedule while setting per-page memory attributes	2025-07-17 18:37:08 +02:00
.clang-format	clang-format: Update with v6.11-rc1's `for_each` macro list	2024-08-02 13:20:31 +02:00
.clippy.toml	rust: give Clippy the minimum supported Rust version	2025-08-01 09:48:44 +01:00
.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	Add Jeff Kirsher to .get_maintainer.ignore	2024-03-08 11:36:54 +00:00
.gitattributes	.gitattributes: set diff driver for Rust source code files	2023-05-31 17:48:25 +02:00
.gitignore	rust: introduce `.clippy.toml`	2025-03-13 13:01:42 +01:00
.mailmap	mailmap: add entry for Thorsten Blum	2024-11-07 14:14:59 -08:00
.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 self from DSA entry	2024-11-03 12:52:38 -08:00
Kbuild	Kbuild updates for v6.1	2022-10-10 12:00:45 -07:00
Kconfig	kbuild: ensure full rebuild when the compiler is updated	2020-05-12 13:28:33 +09:00
MAINTAINERS	MAINTAINERS: Update Alexey Makhalov's email address	2025-05-22 14:29:46 +02:00
Makefile	Linux 6.12.42	2025-08-15 12:14:14 +02:00
README	README: Fix spelling	2024-03-18 03:36:32 -06:00

README

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.