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Steven Rostedt (Google) 5e58483677 ring-buffer: Do not update before stamp when switching sub-buffers 
commit 9e45e39dc2 upstream.

The ring buffer timestamps are synchronized by two timestamp placeholders.
One is the "before_stamp" and the other is the "write_stamp" (sometimes
referred to as the "after stamp" but only in the comments. These two
stamps are key to knowing how to handle nested events coming in with a
lockless system.

When moving across sub-buffers, the before stamp is updated but the write
stamp is not. There's an effort to put back the before stamp to something
that seems logical in case there's nested events. But as the current event
is about to cross sub-buffers, and so will any new nested event that happens,
updating the before stamp is useless, and could even introduce new race
conditions.

The first event on a sub-buffer simply uses the sub-buffer's timestamp
and keeps a "delta" of zero. The "before_stamp" and "write_stamp" are not
used in the algorithm in this case. There's no reason to try to fix the
before_stamp when this happens.

As a bonus, it removes a cmpxchg() when crossing sub-buffers!

Link: https://lore.kernel.org/linux-trace-kernel/20231211114420.36dde01b@gandalf.local.home

Cc: stable@vger.kernel.org
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Fixes: a389d86f7f ("ring-buffer: Have nested events still record running time stamp")
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2023-12-20 17:02:05 +01:00
arch kexec: drop dependency on ARCH_SUPPORTS_KEXEC from CRASH_DUMP 2023-12-20 17:02:03 +01:00
block blk-cgroup: bypass blkcg_deactivate_policy after destroying 2023-12-20 17:01:55 +01:00
certs certs: Reference revocation list for all keyrings 2023-08-17 20:12:41 +00:00
crypto crypto: pcrypt - Fix hungtask for PADATA_RESET 2023-11-28 17:19:42 +00:00
Documentation tee: optee: Fix supplicant based device enumeration 2023-12-13 18:45:11 +01:00
drivers drm/i915: Fix remapped stride with CCS on ADL+ 2023-12-20 17:02:04 +01:00
fs smb: client: fix OOB in smb2_query_reparse_point() 2023-12-20 17:02:05 +01:00
include mm/mglru: reclaim offlined memcgs harder 2023-12-20 17:02:03 +01:00
init proc: sysctl: prevent aliased sysctls from getting passed to init 2023-11-28 17:19:57 +00:00
io_uring io_uring/cmd: fix breakage in SOCKET_URING_OP_SIOC* implementation 2023-12-20 17:01:52 +01:00
ipc Add x86 shadow stack support 2023-08-31 12:20:12 -07:00
kernel ring-buffer: Do not update before stamp when switching sub-buffers 2023-12-20 17:02:05 +01:00
lib cred: get rid of CONFIG_DEBUG_CREDENTIALS 2023-12-20 17:01:51 +01:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm mm/shmem: fix race in shmem_undo_range w/THP 2023-12-20 17:02:03 +01:00
net rxrpc: Fix some minor issues with bundle tracing 2023-12-20 17:01:55 +01:00
rust rust: docs: fix logo replacement 2023-10-19 16:40:00 +02:00
samples samples/bpf: syscall_tp_user: Fix array out-of-bound access 2023-11-28 17:19:48 +00:00
scripts scripts/checkstack.pl: match all stack sizes for s390 2023-12-20 17:01:59 +01:00
security cred: get rid of CONFIG_DEBUG_CREDENTIALS 2023-12-20 17:01:51 +01:00
sound ALSA: hda/tas2781: reset the amp before component_add 2023-12-20 17:01:53 +01:00
tools Revert "selftests: error out if kernel header files are not yet built" 2023-12-20 17:02:01 +01:00
usr initramfs: Encode dependency on KBUILD_BUILD_TIMESTAMP 2023-06-06 17:54:49 +09:00
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: rename binkernel.spec to kernel.spec 2023-07-25 00:59:33 +09:00
.mailmap 20 hotfixes. 12 are cc:stable and the remainder address post-6.5 issues 2023-10-24 09:52:16 -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 Char/Misc driver fixes for 6.6-final 2023-10-28 07:51:27 -10:00
Makefile Linux 6.6.7 2023-12-13 18:45:36 +01:00
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.