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Message-Id: <20221019145600.1282823-1-john.ogness@linutronix.de>
Date: Wed, 19 Oct 2022 17:01:22 +0206
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>,
"Paul E. McKenney" <paulmck@...nel.org>,
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>,
Geert Uytterhoeven <geert@...ux-m68k.org>,
linux-m68k@...ts.linux-m68k.org,
Richard Weinberger <richard@....at>,
Anton Ivanov <anton.ivanov@...bridgegreys.com>,
Johannes Berg <johannes@...solutions.net>,
linux-um@...ts.infradead.org, Ard Biesheuvel <ardb@...nel.org>,
linux-efi@...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,
Shile Zhang <shile.zhang@...ux.alibaba.com>,
Xianting Tian <xianting.tian@...ux.alibaba.com>,
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>,
Mike Rapoport <rppt@...nel.org>,
Mathias Nyman <mathias.nyman@...ux.intel.com>,
Andrew Morton <akpm@...ux-foundation.org>,
linux-usb@...r.kernel.org, Luis Chamberlain <mcgrof@...nel.org>,
Aaron Tomlin <atomlin@...hat.com>,
Helge Deller <deller@....de>,
Thomas Zimmermann <tzimmermann@...e.de>,
Javier Martinez Canillas <javierm@...hat.com>,
Boris Ostrovsky <boris.ostrovsky@...cle.com>,
Juergen Gross <jgross@...e.com>, Tom Rix <trix@...hat.com>,
linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: [PATCH printk v2 00/38] reduce console_lock scope
This is v2 of a series to prepare for threaded/atomic
printing. It is a rework of patches 6-12 of the v1 [0]. From
the v1, patches 1-5 are already mainline and a rework of
patches >12 will be posted in a later series.
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 and is completely removed from
(un)register_console() and console_stop/start() code.
All users of the console_lock for list iteration have been
modified. For the call sites where the console_lock is still
needed (because of other reasons), I added comments to explain
exactly why the console_lock was needed.
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 v2:
general:
- introduce console_is_enabled() to document safe data race on
console->flags
- switch all "console->flags & CON_ENABLED" code sites to
console_is_enabled()
- add "for_each_console_srcu" to .clang-format
- cleanup/clarify comments relating to console_lock
coverage/usage
um:
- kmsg_dumper: use srcu instead of console_lock for list
iteration
kgdb/kdb:
- configure_kgdboc: keep console_lock for console->device()
synchronization, use srcu for list iteration
- kgdboc_earlycon_pre_exp_handler: use srcu instead of
documenting unsafety for list iteration
- kgdboc_earlycon_init: use console_list_lock instead of
console_lock to lock list
- kdb_msg_write: use srcu instead of documenting unsafety for
list iteration
tty:
- show_cons_active: keep console_lock for console->device()
synchronization
fbdev:
- xen-fbfront: xenfb_probe: use srcu instead of console_lock
for list iteration, introduce console_force_preferred() to
safely implement hack
proc/consoles:
- show_console_dev: keep console_lock for console->device()
synchronization
- c_next: use hlist_entry_safe() instead of
hlist_for_each_entry_continue()
printk:
- remove console_lock from console_stop/start() and
(un)register_console()
- introduce console_srcu_read_(un)lock() to wrap scru read
(un)lock
- rename cons_first() macro to console_first()
- for_each_console: add lockdep check instead of introducing
new for_each_registered_console()
- console_list_lock: add warning if in read-side critical
section
- release srcu read lock on handover
- console_flush_all: use srcu instead of relying on console
lock for list iteration
- console_unblank: use srcu instead of relying on console_lock
for list iteration
- console_flush_on_panic: use srcu for list iteration and
document console->seq race
- device: keep console_lock for console->device()
synchronization, usr srcu for list iteration
- register_console: split list adding logic into the 3 distinct
scenarios
- register_console: set initial sequence number before adding
to list
- unregister_console: fix ENODEV return value if the console is
not registered
- console_stop: synchronize srcu
- printk_late_init: use _safe variant of iteration
- __pr_flush: use srcu instead of relying on console_lock for
list iteration
John Ogness
[0] https://lore.kernel.org/r/20220924000454.3319186-1-john.ogness@linutronix.de
[1] https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git/log/?h=srcunmisafe.2022.10.18b
John Ogness (37):
printk: Convert console_drivers list to hlist
printk: Prepare for SRCU console list protection
printk: introduce console_is_enabled() wrapper
printk: use console_is_enabled()
tty: nfcon: use console_is_enabled()
um: kmsg_dump: use console_is_enabled()
efi: earlycon: use console_is_enabled()
netconsole: use console_is_enabled()
tty: hvc: use console_is_enabled()
tty: serial: earlycon: use console_is_enabled()
tty: serial: kgdboc: use console_is_enabled()
tty: serial: pic32_uart: use console_is_enabled()
tty: serial: samsung_tty: use console_is_enabled()
tty: serial: serial_core: use console_is_enabled()
tty: serial: xilinx_uartps: use console_is_enabled()
tty: tty_io: use console_is_enabled()
usb: early: xhci-dbc: use console_is_enabled()
kdb: kdb_io: use console_is_enabled()
um: kmsg_dumper: use srcu console list iterator
serial: kgdboc: use srcu console list iterator
serial: kgdboc: document console_lock usage
tty: tty_io: document console_lock usage
xen: fbfront: use srcu console list iterator
proc: consoles: document console_lock usage
kdb: use srcu console list iterator
printk: console_flush_all: use srcu console list iterator
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
printk: register_console: use srcu console list iterator
printk: __pr_flush: use srcu console list iterator
printk: introduce console_list_lock
serial: kgdboc: use console_list_lock instead of console_lock
tty: tty_io: use console_list_lock for list synchronization
proc: consoles: use console_list_lock for list iteration
printk: relieve console_lock of list synchronization duties
printk, xen: fbfront: create/use safe function for forcing preferred
Thomas Gleixner (1):
serial: kgdboc: Lock console list in probe function
.clang-format | 1 +
arch/m68k/emu/nfcon.c | 4 +-
arch/um/kernel/kmsg_dump.c | 15 +-
drivers/firmware/efi/earlycon.c | 4 +-
drivers/net/netconsole.c | 4 +-
drivers/tty/hvc/hvc_console.c | 2 +-
drivers/tty/serial/earlycon.c | 4 +-
drivers/tty/serial/kgdboc.c | 37 ++-
drivers/tty/serial/pic32_uart.c | 2 +-
drivers/tty/serial/samsung_tty.c | 2 +-
drivers/tty/serial/serial_core.c | 2 +-
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 | 16 +-
fs/proc/consoles.c | 20 +-
include/linux/console.h | 75 +++++-
include/linux/serial_core.h | 2 +-
kernel/debug/kdb/kdb_io.c | 7 +-
kernel/printk/printk.c | 373 +++++++++++++++++++++--------
20 files changed, 438 insertions(+), 154 deletions(-)
base-commit: c2d158a284abd63d727dad7402a2eed650dd4233
--
2.30.2
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