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Marco Elver 701850dc0c printk, tracing: fix console tracepoint 
The original intent of the 'console' tracepoint per the commit 9510035849
("printk/tracing: Add console output tracing") had been to "[...] record
any printk messages into the trace, regardless of the current console
loglevel. This can help correlate (existing) printk debugging with other
tracing."

Petr points out [1] that calling trace_console_rcuidle() in
call_console_driver() had been the wrong thing for a while, because
"printk() always used console_trylock() and the message was flushed to
the console only when the trylock succeeded. And it was always deferred
in NMI or when printed via printk_deferred()."

With the commit 09c5ba0aa2 ("printk: add kthread console printers"),
things only got worse, and calls to call_console_driver() no longer
happen with typical printk() calls but always appear deferred [2].

As such, the tracepoint can no longer serve its purpose to clearly
correlate printk() calls and other tracing, as well as breaks usecases
that expect every printk() call to result in a callback of the console
tracepoint. Notably, the KFENCE and KCSAN test suites, which want to
capture console output and assume a printk() immediately gives us a
callback to the console tracepoint.

Fix the console tracepoint by moving it into printk_sprint() [3].

One notable difference is that by moving tracing into printk_sprint(),
the 'text' will no longer include the "header" (loglevel and timestamp),
but only the raw message. Arguably this is less of a problem now that
the console tracepoint happens on the printk() call and isn't delayed.

Link: https://lore.kernel.org/all/Ym+WqKStCg%2FEHfh3@alley/ [1]
Link: https://lore.kernel.org/all/CA+G9fYu2kS0wR4WqMRsj2rePKV9XLgOU1PiXnMvpT+Z=c2ucHA@mail.gmail.com/ [2]
Link: https://lore.kernel.org/all/87fslup9dx.fsf@jogness.linutronix.de/ [3]
Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
Signed-off-by: Marco Elver <elver@google.com>
Cc: John Ogness <john.ogness@linutronix.de>
Cc: Petr Mladek <pmladek@suse.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Acked-by: John Ogness <john.ogness@linutronix.de>
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220503073844.4148944-1-elver@google.com
2022-05-06 10:55:24 +02:00
arch Folio changes for 5.18 2022-03-22 17:03:12 -07:00
block Filesystem folio changes for 5.18 2022-03-22 18:26:56 -07:00
certs KEYS: Introduce link restriction for machine keys 2022-03-08 13:55:52 +02:00
crypto Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2022-03-21 16:02:36 -07:00
Documentation printk changes for 5.18 2022-03-23 10:54:27 -07:00
drivers printk: add functions to prefer direct printing 2022-04-22 21:30:58 +02:00
fs Filesystem folio changes for 5.18 2022-03-22 18:26:56 -07:00
include printk: extend console_lock for per-console locking 2022-04-26 14:32:00 +02:00
init Changes in this cycle were: 2022-03-22 14:39:12 -07:00
ipc fs: allocate inode by using alloc_inode_sb() 2022-03-22 15:57:03 -07:00
kernel printk, tracing: fix console tracepoint 2022-05-06 10:55:24 +02:00
lib printk: rename cpulock functions 2022-04-22 21:30:57 +02:00
LICENSES LICENSES/LGPL-2.1: Add LGPL-2.1-or-later as valid identifiers 2021-12-16 14:33:10 +01:00
mm Filesystem folio changes for 5.18 2022-03-22 18:26:56 -07:00
net Merge branch 'akpm' (patches from Andrew) 2022-03-22 16:11:53 -07:00
samples samples/seccomp: Adjust sample to also provide kill option 2022-02-10 19:09:12 -08:00
scripts Merge branch 'akpm' (patches from Andrew) 2022-03-22 16:11:53 -07:00
security selinux/stable-5.18 PR 20220321 2022-03-21 20:47:54 -07:00
sound spi: Updates for v5.18 2022-03-21 18:33:57 -07:00
tools Folio changes for 5.18 2022-03-22 17:03:12 -07:00
usr kbuild: remove include/linux/cyclades.h from header file check 2022-01-27 08:51:08 +01:00
virt KVM: Fix lockdep false negative during host resume 2022-02-17 09:52:50 -05:00
.clang-format genirq/msi: Make interrupt allocation less convoluted 2021-12-16 22:22:20 +01:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap MAINTAINERS: Update Jisheng's email address 2022-03-08 17:30:32 +01:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: replace a Microchip AT91 maintainer 2022-02-09 11:30:01 +01:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS Merge branch 'akpm' (patches from Andrew) 2022-03-22 16:11:53 -07:00
Makefile Linux 5.17 2022-03-20 13:14:17 -07:00
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.