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Date: Wed, 16 Nov 2022 17:27:12 +0106
From: John Ogness <john.ogness@...utronix.de>
To: Petr Mladek <pmladek@...e.com>
Cc: Sergey Senozhatsky <senozhatsky@...omium.org>,
Steven Rostedt <rostedt@...dmis.org>,
Thomas Gleixner <tglx@...utronix.de>,
linux-kernel@...r.kernel.org,
Jason Wessel <jason.wessel@...driver.com>,
Daniel Thompson <daniel.thompson@...aro.org>,
Douglas Anderson <dianders@...omium.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Jiri Slaby <jirislaby@...nel.org>,
kgdb-bugreport@...ts.sourceforge.net, linux-serial@...r.kernel.org,
linux-fsdevel@...r.kernel.org, Miguel Ojeda <ojeda@...nel.org>,
Richard Weinberger <richard@....at>,
Anton Ivanov <anton.ivanov@...bridgegreys.com>,
Johannes Berg <johannes@...solutions.net>,
linux-um@...ts.infradead.org, Aaron Tomlin <atomlin@...hat.com>,
Luis Chamberlain <mcgrof@...nel.org>,
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
Lukas Wunner <lukas@...ner.de>,
Geert Uytterhoeven <geert+renesas@...der.be>,
Geert Uytterhoeven <geert@...ux-m68k.org>,
linux-m68k@...ts.linux-m68k.org, Ard Biesheuvel <ardb@...nel.org>,
linux-efi@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
Alim Akhtar <alim.akhtar@...sung.com>,
linux-arm-kernel@...ts.infradead.org,
linux-samsung-soc@...r.kernel.org,
Michal Simek <michal.simek@...inx.com>,
Peter Zijlstra <peterz@...radead.org>,
Mathias Nyman <mathias.nyman@...ux.intel.com>,
linux-usb@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
Helge Deller <deller@....de>,
Thomas Zimmermann <tzimmermann@...e.de>,
Javier Martinez Canillas <javierm@...hat.com>,
Juergen Gross <jgross@...e.com>,
Boris Ostrovsky <boris.ostrovsky@...cle.com>,
Tom Rix <trix@...hat.com>, linux-fbdev@...r.kernel.org,
dri-devel@...ts.freedesktop.org
Subject: [PATCH printk v5 00/40] reduce console_lock scope
This is v5 of a series to prepare for threaded/atomic
printing. v4 is here [0]. This series focuses on reducing the
scope of the BKL console_lock. It achieves this by switching to
SRCU and a dedicated mutex for console list iteration and
modification, respectively. The console_lock will no longer
offer this protection.
Also, during the review of v2 it came to our attention that
many console drivers are checking CON_ENABLED to see if they
are registered. Because this flag can change without
unregistering and because this flag does not represent an
atomic point when an (un)registration process is complete,
a new console_is_registered() function is introduced. This
function uses the console_list_lock to synchronize with the
(un)registration process to provide a reliable status.
All users of the console_lock for list iteration have been
modified. For the call sites where the console_lock is still
needed (for other reasons), comments are added to explain
exactly why the console_lock is needed.
All users of CON_ENABLED for registration status have been
modified to use console_is_registered(). Note that there are
still users of CON_ENABLED, but this is for legitimate purposes
about a registered console being able to print.
The base commit for this series is from Paul McKenney's RCU tree
and provides an NMI-safe SRCU implementation [1]. Without the
NMI-safe SRCU implementation, this series is not less safe than
mainline. But we will need the NMI-safe SRCU implementation for
atomic consoles anyway, so we might as well get it in
now. Especially since it _does_ increase the reliability for
mainline in the panic path.
Changes since v4:
printk:
- Introduce console_init_seq() to handle the now rather complex
procedure to find an appropriate start sequence number for a
new console upon registration.
- When registering a non-boot console and boot consoles are
registered, try to flush all the consoles to get the next @seq
value before falling back to use the @seq of the enabled boot
console that is furthest behind.
- For console_force_preferred_locked(), make the console the
head of the console list.
John Ogness
[0] https://lore.kernel.org/lkml/20221114162932.141883-1-john.ogness@linutronix.de
[1] https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git/log/?h=srcunmisafe.2022.11.09a
John Ogness (38):
printk: Prepare for SRCU console list protection
printk: register_console: use "registered" for variable names
printk: move @seq initialization to helper
printk: fix setting first seq for consoles
um: kmsg_dump: only dump when no output console available
tty: serial: kgdboc: document console_lock usage
tty: tty_io: document console_lock usage
proc: consoles: document console_lock usage
printk: introduce console_list_lock
console: introduce wrappers to read/write console flags
um: kmsg_dumper: use srcu console list iterator
kdb: use srcu console list iterator
printk: console_flush_all: use srcu console list iterator
printk: __pr_flush: use srcu console list iterator
printk: console_is_usable: use console_srcu_read_flags
printk: console_unblank: use srcu console list iterator
printk: console_flush_on_panic: use srcu console list iterator
printk: console_device: use srcu console list iterator
console: introduce console_is_registered()
serial_core: replace uart_console_enabled() with
uart_console_registered()
tty: nfcon: use console_is_registered()
efi: earlycon: use console_is_registered()
tty: hvc: use console_is_registered()
tty: serial: earlycon: use console_is_registered()
tty: serial: pic32_uart: use console_is_registered()
tty: serial: samsung_tty: use console_is_registered()
tty: serial: xilinx_uartps: use console_is_registered()
usb: early: xhci-dbc: use console_is_registered()
netconsole: avoid CON_ENABLED misuse to track registration
printk, xen: fbfront: create/use safe function for forcing preferred
tty: tty_io: use console_list_lock for list synchronization
proc: consoles: use console_list_lock for list iteration
tty: serial: kgdboc: use srcu console list iterator
tty: serial: kgdboc: use console_list_lock for list traversal
tty: serial: kgdboc: synchronize tty_find_polling_driver() and
register_console()
tty: serial: kgdboc: use console_list_lock to trap exit
printk: relieve console_lock of list synchronization duties
tty: serial: sh-sci: use setup() callback for early console
Thomas Gleixner (2):
serial: kgdboc: Lock console list in probe function
printk: Convert console_drivers list to hlist
.clang-format | 1 +
arch/m68k/emu/nfcon.c | 9 +-
arch/um/kernel/kmsg_dump.c | 24 +-
drivers/firmware/efi/earlycon.c | 8 +-
drivers/net/netconsole.c | 21 +-
drivers/tty/hvc/hvc_console.c | 4 +-
drivers/tty/serial/8250/8250_core.c | 2 +-
drivers/tty/serial/earlycon.c | 4 +-
drivers/tty/serial/kgdboc.c | 46 ++-
drivers/tty/serial/pic32_uart.c | 4 +-
drivers/tty/serial/samsung_tty.c | 2 +-
drivers/tty/serial/serial_core.c | 14 +-
drivers/tty/serial/sh-sci.c | 20 +-
drivers/tty/serial/xilinx_uartps.c | 2 +-
drivers/tty/tty_io.c | 18 +-
drivers/usb/early/xhci-dbc.c | 2 +-
drivers/video/fbdev/xen-fbfront.c | 12 +-
fs/proc/consoles.c | 21 +-
include/linux/console.h | 129 +++++++-
include/linux/serial_core.h | 10 +-
kernel/debug/kdb/kdb_io.c | 18 +-
kernel/printk/printk.c | 493 +++++++++++++++++++++-------
22 files changed, 680 insertions(+), 184 deletions(-)
base-commit: f733615e39aa2d6ddeef33b7b2c9aa6a5a2c2785
--
2.30.2
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