--- v3
+++ v2
@@ -1,29 +1,19 @@
-This is v3 of a series to prepare for threaded/atomic
-printing. v2 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 and is completely removed from
+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.
-
-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 (because of other reasons), comments are added to
-explain exactly why the console_lock was 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.
+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
@@ -33,171 +23,176 @@
now. Especially since it _does_ increase the reliability for
mainline in the panic path.
-Changes since v3:
+Changes since v2:
general:
-- introduce a synchronized console_is_registered() to query if
- a console is registered, meant to replace CON_ENABLED
- (mis)use for this purpose
+- introduce console_is_enabled() to document safe data race on
+ console->flags
-- directly read console->flags for registered consoles if it is
- race-free (and document that it is so)
+- switch all "console->flags & CON_ENABLED" code sites to
+ console_is_enabled()
-- replace uart_console_enabled() with a new
- uart_console_registered() based on console_is_registered()
+- add "for_each_console_srcu" to .clang-format
-- change comments about why console_lock is used to synchronize
- console->device() by providing an example
+- cleanup/clarify comments relating to console_lock
+ coverage/usage
-registration check fixups:
+um:
-- the following drivers were modified to use the new
- console_is_registered() instead of CON_ENABLED checks
-
- - arch/m68k/emu/nfcon.c
- - drivers/firmware/efi/earlycon.c
- - drivers/net/netconsole.c
- - drivers/tty/hvc/hvc_console.c
- - drivers/tty/serial/8250/8250_core.c
- - drivers/tty/serial/earlycon.c
- - drivers/tty/serial/pic32_uart.c
- - drivers/tty/serial/samsung_tty.c
- - drivers/tty/serial/serial_core.c
- - drivers/tty/serial/xilinx_uartps.c
- - drivers/usb/early/xhci-dbc.c
-
-um: kmsg_dumper:
-
-- change stdout dump criteria to match original intention
+- kmsg_dumper: use srcu instead of console_lock for list
+ iteration
kgdb/kdb:
-- in configure_kgdboc(), take console_list_lock to synchronize
- tty_find_polling_driver() against register_console()
+- configure_kgdboc: keep console_lock for console->device()
+ synchronization, use srcu for list iteration
-- add comments explaining why calling console->write() without
- locking might work
+- kgdboc_earlycon_pre_exp_handler: use srcu instead of
+ documenting unsafety for list iteration
-tty: sh-sci:
+- kgdboc_earlycon_init: use console_list_lock instead of
+ console_lock to lock list
-- use a setup() callback to setup the early console
+- kdb_msg_write: use srcu instead of documenting unsafety for
+ list iteration
-fbdev: xen:
+tty:
-- implement a cleaner approach for
- console_force_preferred_locked()
+- show_cons_active: keep console_lock for console->device()
+ synchronization
-rcu:
+fbdev:
-- implement debug_lockdep_rcu_enabled() for
- !CONFIG_DEBUG_LOCK_ALLOC
+- 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:
-- check CONFIG_DEBUG_LOCK_ALLOC for srcu_read_lock_held()
- availability
+- remove console_lock from console_stop/start() and
+ (un)register_console()
-- for console_lock/_trylock/_unlock, replace "lock the console
- system" language with "block the console subsystem from
- printing"
+- introduce console_srcu_read_(un)lock() to wrap scru read
+ (un)lock
-- use WRITE_ONCE() for updating console->flags of registered
- consoles
+- rename cons_first() macro to console_first()
-- expand comments of synchronize_srcu() calls to explain why
- they are needed, and also expand comments to explain when it
- is not needed
+- for_each_console: add lockdep check instead of introducing
+ new for_each_registered_console()
-- change CON_BOOT consoles to always begin at earliest message
+- console_list_lock: add warning if in read-side critical
+ section
-- for non-BOOT/non-PRINTBUFFER consoles, initialize @seq to the
- minimal @seq of any of the enabled boot consoles
+- release srcu read lock on handover
-- add comments and lockdep assertion to
- unregister_console_locked() because it is not clear from the
- name which lock is implied
+- console_flush_all: use srcu instead of relying on console
+ lock for list iteration
-- dropped patches that caused unnecessary churn in the series
+- 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/lkml/20221019145600.1282823-1-john.ogness@linutronix.de
-[1] https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git/log/?h=srcunmisafe.2022.10.21a
+[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 (38):
- rcu: implement lockdep_rcu_enabled for !CONFIG_DEBUG_LOCK_ALLOC
+John Ogness (37):
+ printk: Convert console_drivers list to hlist
printk: Prepare for SRCU console list protection
- printk: fix setting first seq for consoles
- um: kmsg_dump: only dump when no output console available
- console: introduce console_is_enabled() wrapper
+ 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
- tty: serial: kgdboc: document console_lock usage
+ 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
- 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
+ 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
- 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
+ printk, xen: fbfront: create/use safe function for forcing preferred
-Thomas Gleixner (2):
+Thomas Gleixner (1):
serial: kgdboc: Lock console list in probe function
- printk: Convert console_drivers list to hlist
- .clang-format | 1 +
- arch/m68k/emu/nfcon.c | 10 +-
- 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 | 17 +-
- 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 | 111 +++++++-
- include/linux/rcupdate.h | 5 +
- include/linux/serial_core.h | 15 +-
- kernel/debug/kdb/kdb_io.c | 14 +-
- kernel/printk/printk.c | 424 +++++++++++++++++++++-------
- 23 files changed, 605 insertions(+), 176 deletions(-)
+ .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: e29a4915db1480f96e0bc2e928699d086a71f43c
+base-commit: c2d158a284abd63d727dad7402a2eed650dd4233
--
2.30.2