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Linus Torvalds 55cb5f4368 tracing fix for 6.7-rc6 While working on the ring buffer, I found one more bug with the timestamp code, and the fix for this removed the need for the final 64-bit cmpxchg! The ring buffer events hold a "delta" from the previous event. If it is determined that the delta can not be calculated, it falls back to adding an absolute timestamp value. The way to know if the delta can be used is via two stored timestamps in the per-cpu buffer meta data: before_stamp and write_stamp The before_stamp is written by every event before it tries to allocate its space on the ring buffer. The write_stamp is written after it allocates its space and knows that nothing came in after it read the previous before_stamp and write_stamp and the two matched. A previous fix `dd93942570` ("ring-buffer: Do not try to put back write_stamp") removed putting back the write_stamp to match the before_stamp so that the next event could use the delta, but races were found where the two would match, but not be for of the previous event. It was determined to allow the event reservation to not have a valid write_stamp when it is finished, and this fixed a lot of races. The last use of the 64-bit timestamp cmpxchg depended on the write_stamp being valid after an interruption. But this is no longer the case, as if an event is interrupted by a softirq that writes an event, and that event gets interrupted by a hardirq or NMI and that writes an event, then the softirq could finish its reservation without a valid write_stamp. In the slow path of the event reservation, a delta can still be used if the write_stamp is valid. Instead of using a cmpxchg against the write stamp, the before_stamp needs to be read again to validate the write_stamp. The cmpxchg is not needed. This updates the slowpath to validate the write_stamp by comparing it to the before_stamp and removes all rb_time_cmpxchg() as there are no more users of that function. The removal of the 32-bit updates of rb_time_t will be done in the next merge window. -----BEGIN PGP SIGNATURE----- iIoEABYIADIWIQRRSw7ePDh/lE+zeZMp5XQQmuv6qgUCZYHVxhQccm9zdGVkdEBn b29kbWlzLm9yZwAKCRAp5XQQmuv6qhk5AQDT56Uis34ewzeEzkwBSs8nsV2HDhnA d0CU4BHsf0GUVQD9E2eWVbIB9z8MiQwNMvKslpFJYmGCzr359pCMzoOmcws= =0rcD -----END PGP SIGNATURE----- Merge tag 'trace-v6.7-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace Pull tracing fix from Steven Rostedt: "While working on the ring buffer, I found one more bug with the timestamp code, and the fix for this removed the need for the final 64-bit cmpxchg! The ring buffer events hold a "delta" from the previous event. If it is determined that the delta can not be calculated, it falls back to adding an absolute timestamp value. The way to know if the delta can be used is via two stored timestamps in the per-cpu buffer meta data: before_stamp and write_stamp The before_stamp is written by every event before it tries to allocate its space on the ring buffer. The write_stamp is written after it allocates its space and knows that nothing came in after it read the previous before_stamp and write_stamp and the two matched. A previous fix `dd93942570` ("ring-buffer: Do not try to put back write_stamp") removed putting back the write_stamp to match the before_stamp so that the next event could use the delta, but races were found where the two would match, but not be for of the previous event. It was determined to allow the event reservation to not have a valid write_stamp when it is finished, and this fixed a lot of races. The last use of the 64-bit timestamp cmpxchg depended on the write_stamp being valid after an interruption. But this is no longer the case, as if an event is interrupted by a softirq that writes an event, and that event gets interrupted by a hardirq or NMI and that writes an event, then the softirq could finish its reservation without a valid write_stamp. In the slow path of the event reservation, a delta can still be used if the write_stamp is valid. Instead of using a cmpxchg against the write stamp, the before_stamp needs to be read again to validate the write_stamp. The cmpxchg is not needed. This updates the slowpath to validate the write_stamp by comparing it to the before_stamp and removes all rb_time_cmpxchg() as there are no more users of that function. The removal of the 32-bit updates of rb_time_t will be done in the next merge window" * tag 'trace-v6.7-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: ring-buffer: Fix slowpath of interrupted event		2023-12-19 12:25:43 -08:00
arch	ARC fixes for 6.7	2023-12-19 12:19:25 -08:00
block	block-6.7-2023-12-01	2023-12-02 06:39:30 +09:00
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	drm fixes for 6.7-rc6	2023-12-15 11:07:13 -08:00
drivers	hid-for-linus-2023121901	2023-12-18 16:47:21 -08:00
fs	for-6.7-rc5-tag	2023-12-17 09:27:36 -08:00
include	pci-v6.7-fixes-1	2023-12-15 19:48:47 -08:00
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/cmd: fix breakage in SOCKET_URING_OP_SIOC* implementation	2023-12-14 16:52:13 -07:00
ipc	Many singleton patches against the MM code. The patch series which are	2023-11-02 19:38:47 -10:00
kernel	tracing fix for 6.7-rc6	2023-12-19 12:25:43 -08:00
lib	cred: get rid of CONFIG_DEBUG_CREDENTIALS	2023-12-15 14:19:48 -08:00
LICENSES	LICENSES: Add the copyleft-next-0.3.1 license	2022-11-08 15:44:01 +01:00
mm	mm/mglru: reclaim offlined memcgs harder	2023-12-12 17:20:20 -08:00
net	cred: get rid of CONFIG_DEBUG_CREDENTIALS	2023-12-15 14:19:48 -08:00
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	sign-file: Fix incorrect return values check	2023-12-13 12:55:11 -08:00
security	cred: get rid of CONFIG_DEBUG_CREDENTIALS	2023-12-15 14:19:48 -08:00
sound	ALSA: hda/tas2781: reset the amp before component_add	2023-12-14 12:04:38 +01:00
tools	cxl fixes for 6.7-rc6	2023-12-17 09:07:34 -08:00
usr	arch: Remove Itanium (IA-64) architecture	2023-09-11 08:13:17 +00:00
virt	Revert "KVM: Prevent module exit until all VMs are freed"	2023-12-01 08:12:30 -08:00
.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	hid-for-linus-2023121201	2023-12-12 17:02:56 -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: drop Antti Palosaari	2023-12-06 16:12:49 -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	powerpc fixes for 6.7 #5	2023-12-17 08:50:00 -08:00
Makefile	Linux 6.7-rc6	2023-12-17 15:19:28 -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.