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Paul E. McKenney 4e58aaeebb rcu: Restrict access to RCU CPU stall notifiers Although the RCU CPU stall notifiers can be useful for dumping state when tracking down delicate forward-progress bugs where NUMA effects cause cache lines to be delivered to a given CPU regularly, but always in a state that prevents that CPU from making forward progress. These bugs can be detected by the RCU CPU stall-warning mechanism, but in some cases, the stall-warnings printk()s disrupt the forward-progress bug before any useful state can be obtained. Unfortunately, the notifier mechanism added by commit `5b404fdaba` ("rcu: Add RCU CPU stall notifier") can make matters worse if used at all carelessly. For example, if the stall warning was caused by a lock not being released, then any attempt to acquire that lock in the notifier will hang. This will prevent not only the notifier from producing any useful output, but it will also prevent the stall-warning message from ever appearing. This commit therefore hides this new RCU CPU stall notifier mechanism under a new RCU_CPU_STALL_NOTIFIER Kconfig option that depends on both DEBUG_KERNEL and RCU_EXPERT. In addition, the rcupdate.rcu_cpu_stall_notifiers=1 kernel boot parameter must also be specified. The RCU_CPU_STALL_NOTIFIER Kconfig option's help text contains a warning and explains the dangers of careless use, recommending lockless notifier code. In addition, a WARN() is triggered each time that an attempt is made to register a stall-warning notifier in kernels built with CONFIG_RCU_CPU_STALL_NOTIFIER=y. This combination of measures will keep use of this mechanism confined to debug kernels and away from routine deployments. [ paulmck: Apply Dan Carpenter feedback. ] Fixes: `5b404fdaba` ("rcu: Add RCU CPU stall notifier") Reported-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org> Signed-off-by: Neeraj Upadhyay (AMD) <neeraj.iitr10@gmail.com>		2023-12-12 02:31:22 +05:30
arch	- Ignore invalid x2APIC entries in order to not waste per-CPU data	2023-11-19 13:46:17 -08:00
block	blk-mq: make sure active queue usage is held for bio_integrity_prep()	2023-11-13 08:52:52 -07:00
certs	This update includes the following changes:	2023-11-02 16:15:30 -10:00
crypto	This push fixes a regression in ahash and hides the Kconfig sub-options for the jitter RNG.	2023-11-09 17:04:58 -08:00
Documentation	rcu: Restrict access to RCU CPU stall notifiers	2023-12-12 02:31:22 +05:30
drivers	- Flush the translation service tables to prevent unpredictable behavior	2023-11-19 13:49:32 -08:00
fs	Bug fixes for 6.7-rc2:	2023-11-18 11:28:28 -08:00
include	rcu: Restrict access to RCU CPU stall notifiers	2023-12-12 02:31:22 +05:30
init	As usual, lots of singleton and doubleton patches all over the tree and	2023-11-02 20:53:31 -10:00
io_uring	io_uring/fdinfo: remove need for sqpoll lock for thread/pid retrieval	2023-11-15 06:35:46 -07:00
ipc	Many singleton patches against the MM code. The patch series which are	2023-11-02 19:38:47 -10:00
kernel	rcu: Restrict access to RCU CPU stall notifiers	2023-12-12 02:31:22 +05:30
lib	Zstd fixes for v6.7	2023-11-14 23:35:31 -05:00
LICENSES	LICENSES: Add the copyleft-next-0.3.1 license	2022-11-08 15:44:01 +01:00
mm	mm: more ptep_get() conversion	2023-11-15 15:30:09 -08:00
net	netfilter pull request 23-11-15	2023-11-16 11:02:52 +01:00
rust	Kbuild updates for v6.7	2023-11-04 08:07:19 -10:00
samples	Landlock updates for v6.7-rc1	2023-11-03 09:28:53 -10:00
scripts	Kbuild fixes for v6.7	2023-11-19 13:54:28 -08:00
security	+ Features	2023-11-03 09:48:17 -10:00
sound	sound fixes for 6.7-rc2	2023-11-17 09:05:31 -05:00
tools	turbostat-2023.11.07	2023-11-18 09:09:17 -08:00
usr	arch: Remove Itanium (IA-64) architecture	2023-09-11 08:13:17 +00:00
virt	ARM:	2023-09-07 13:52:20 -07:00
.clang-format	iommu: Add for_each_group_device()	2023-05-23 08:15:51 +02:00
.cocciconfig	scripts: add Linux .cocciconfig for coccinelle	2016-07-22 12:13:39 +02:00
.get_maintainer.ignore	get_maintainer: add Alan to .get_maintainer.ignore	2022-08-20 15:17:44 -07:00
.gitattributes	.gitattributes: set diff driver for Rust source code files	2023-05-31 17:48:25 +02:00
.gitignore	kbuild: rpm-pkg: generate kernel.spec in rpmbuild/SPECS/	2023-10-03 20:49:09 +09:00
.mailmap	As usual, lots of singleton and doubleton patches all over the tree and	2023-11-02 20:53:31 -10:00
.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	USB: Remove Wireless USB and UWB documentation	2023-08-09 14:17:32 +02:00
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	- Ignore invalid x2APIC entries in order to not waste per-CPU data	2023-11-19 13:46:17 -08:00
Makefile	Linux 6.7-rc2	2023-11-19 15:02:14 -08:00
README	Drop all 00-INDEX files from Documentation/	2018-09-09 15:08:58 -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 Restructured Text 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.