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Petr Mladek d04d5882cd printk: Disable passing console lock owner completely during panic() 
The commit d51507098f ("printk: disable optimistic spin
during panic") added checks to avoid becoming a console waiter
if a panic is in progress.

However, the transition to panic can occur while there is
already a waiter. The current owner should not pass the lock to
the waiter because it might get stopped or blocked anytime.

Also the panic context might pass the console lock owner to an
already stopped waiter by mistake. It might happen when
console_flush_on_panic() ignores the current lock owner, for
example:

CPU0                                CPU1
----                                ----
console_lock_spinning_enable()
                                    console_trylock_spinning()
                                      [CPU1 now console waiter]
NMI: panic()
  panic_other_cpus_shutdown()
                                    [stopped as console waiter]
  console_flush_on_panic()
    console_lock_spinning_enable()
    [print 1 record]
    console_lock_spinning_disable_and_check()
      [handover to stopped CPU1]

This results in panic() not flushing the panic messages.

Fix these problems by disabling all spinning operations
completely during panic().

Another advantage is that it prevents possible deadlocks caused
by "console_owner_lock". The panic() context does not need to
take it any longer. The lockless checks are safe because the
functions become NOPs when they see the panic in progress. All
operations manipulating the state are still synchronized by the
lock even when non-panic CPUs would notice the panic
synchronously.

The current owner might stay spinning. But non-panic() CPUs
would get stopped anyway and the panic context will never start
spinning.

Fixes: dbdda842fe ("printk: Add console owner and waiter logic to load balance console writes")
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Link: https://lore.kernel.org/r/20240207134103.1357162-12-john.ogness@linutronix.de
Signed-off-by: Petr Mladek <pmladek@suse.com>
History 2024-02-07 17:23:18 +01:00
arch As usual, lots of singleton and doubleton patches all over the tree and 2023-11-02 20:53:31 -10:00
block As usual, lots of singleton and doubleton patches all over the tree and 2023-11-02 20:53:31 -10:00
certs This update includes the following changes: 2023-11-02 16:15:30 -10:00
crypto This update includes the following changes: 2023-11-02 16:15:30 -10:00
Documentation Many singleton patches against the MM code. The patch series which are 2023-11-02 19:38:47 -10:00
drivers As usual, lots of singleton and doubleton patches all over the tree and 2023-11-02 20:53:31 -10:00
fs As usual, lots of singleton and doubleton patches all over the tree and 2023-11-02 20:53:31 -10:00
include printk changes for 6.7 2023-11-03 07:24:22 -10:00
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-futex-2023-10-30 2023-11-01 11:25:08 -10:00
ipc Many singleton patches against the MM code. The patch series which are 2023-11-02 19:38:47 -10:00
kernel printk: Disable passing console lock owner completely during panic() 2024-02-07 17:23:18 +01:00
lib printk changes for 6.7 2023-11-03 07:24:22 -10:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm As usual, lots of singleton and doubleton patches all over the tree and 2023-11-02 20:53:31 -10:00
net As usual, lots of singleton and doubleton patches all over the tree and 2023-11-02 20:53:31 -10:00
rust workqueue: Add rust bindings for v6.7 2023-10-30 20:35:48 -10:00
samples Probes updates for v6.7: 2023-11-01 16:15:42 -10:00
scripts As usual, lots of singleton and doubleton patches all over the tree and 2023-11-02 20:53:31 -10:00
security As usual, lots of singleton and doubleton patches all over the tree and 2023-11-02 20:53:31 -10:00
sound As usual, lots of singleton and doubleton patches all over the tree and 2023-11-02 20:53:31 -10:00
tools As usual, lots of singleton and doubleton patches all over the tree and 2023-11-02 20:53:31 -10:00
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: rename binkernel.spec to kernel.spec 2023-07-25 00:59:33 +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 bitmap patches for v6.7 2023-11-03 07:08:36 -10:00
Makefile linux_kselftest-next-6.7-rc1 2023-11-01 17:08:10 -10:00
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.