* [PATCH printk v5 00/40] reduce console_lock scope
@ 2022-11-16 16:21 John Ogness
2022-11-16 16:21 ` [PATCH printk v5 23/40] tty: nfcon: use console_is_registered() John Ogness
` (2 more replies)
0 siblings, 3 replies; 6+ messages in thread
From: John Ogness @ 2022-11-16 16:21 UTC (permalink / raw)
To: Petr Mladek
Cc: Sergey Senozhatsky, Steven Rostedt, Thomas Gleixner,
linux-kernel, Jason Wessel, Daniel Thompson, Douglas Anderson,
Greg Kroah-Hartman, Jiri Slaby, kgdb-bugreport, linux-serial,
linux-fsdevel, Miguel Ojeda, Richard Weinberger, Anton Ivanov,
Johannes Berg, linux-um, Aaron Tomlin, Luis Chamberlain,
Andy Shevchenko, Ilpo Järvinen, Lukas Wunner,
Geert Uytterhoeven, Geert Uytterhoeven, linux-m68k,
Ard Biesheuvel, linux-efi, linuxppc-dev, Krzysztof Kozlowski,
Alim Akhtar, linux-arm-kernel, linux-samsung-soc, Michal Simek,
Peter Zijlstra, Mathias Nyman, linux-usb, David S. Miller,
Eric Dumazet, Jakub Kicinski, Paolo Abeni, netdev, Helge Deller,
Thomas Zimmermann, Javier Martinez Canillas, Juergen Gross,
Boris Ostrovsky, Tom Rix, linux-fbdev, dri-devel
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
^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH printk v5 23/40] tty: nfcon: use console_is_registered()
2022-11-16 16:21 [PATCH printk v5 00/40] reduce console_lock scope John Ogness
@ 2022-11-16 16:21 ` John Ogness
2022-11-17 8:18 ` Geert Uytterhoeven
2022-11-18 11:22 ` [PATCH printk v5 00/40] reduce console_lock scope Petr Mladek
2022-11-22 16:43 ` Greg Kroah-Hartman
2 siblings, 1 reply; 6+ messages in thread
From: John Ogness @ 2022-11-16 16:21 UTC (permalink / raw)
To: Petr Mladek
Cc: Sergey Senozhatsky, Steven Rostedt, Thomas Gleixner,
linux-kernel, Geert Uytterhoeven, linux-m68k
Currently CON_ENABLED is being (mis)used to identify if the console
has been registered. This is not reliable because it can be set even
though registration failed or it can be unset, even though the console
is registered. Use console_is_registered() instead.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
---
arch/m68k/emu/nfcon.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/arch/m68k/emu/nfcon.c b/arch/m68k/emu/nfcon.c
index 557d60867f98..6fdc13610565 100644
--- a/arch/m68k/emu/nfcon.c
+++ b/arch/m68k/emu/nfcon.c
@@ -49,7 +49,7 @@ static void nfcon_write(struct console *con, const char *str,
static struct tty_driver *nfcon_device(struct console *con, int *index)
{
*index = 0;
- return (con->flags & CON_ENABLED) ? nfcon_tty_driver : NULL;
+ return console_is_registered(con) ? nfcon_tty_driver : NULL;
}
static struct console nf_console = {
@@ -107,6 +107,11 @@ static int __init nf_debug_setup(char *arg)
stderr_id = nf_get_id("NF_STDERR");
if (stderr_id) {
+ /*
+ * The console will be enabled when debug=nfcon is specified
+ * as a kernel parameter. Since this is a non-standard way
+ * of enabling consoles, it must be explicitly enabled.
+ */
nf_console.flags |= CON_ENABLED;
register_console(&nf_console);
}
@@ -151,7 +156,7 @@ static int __init nfcon_init(void)
nfcon_tty_driver = driver;
- if (!(nf_console.flags & CON_ENABLED))
+ if (!console_is_registered(&nf_console))
register_console(&nf_console);
return 0;
--
2.30.2
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH printk v5 23/40] tty: nfcon: use console_is_registered()
2022-11-16 16:21 ` [PATCH printk v5 23/40] tty: nfcon: use console_is_registered() John Ogness
@ 2022-11-17 8:18 ` Geert Uytterhoeven
0 siblings, 0 replies; 6+ messages in thread
From: Geert Uytterhoeven @ 2022-11-17 8:18 UTC (permalink / raw)
To: John Ogness
Cc: Petr Mladek, Sergey Senozhatsky, Steven Rostedt, Thomas Gleixner,
linux-kernel, linux-m68k
On Wed, Nov 16, 2022 at 5:22 PM John Ogness <john.ogness@linutronix.de> wrote:
> Currently CON_ENABLED is being (mis)used to identify if the console
> has been registered. This is not reliable because it can be set even
> though registration failed or it can be unset, even though the console
> is registered. Use console_is_registered() instead.
>
> Signed-off-by: John Ogness <john.ogness@linutronix.de>
> Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH printk v5 00/40] reduce console_lock scope
2022-11-16 16:21 [PATCH printk v5 00/40] reduce console_lock scope John Ogness
2022-11-16 16:21 ` [PATCH printk v5 23/40] tty: nfcon: use console_is_registered() John Ogness
@ 2022-11-18 11:22 ` Petr Mladek
2022-11-18 14:55 ` Petr Mladek
2022-11-22 16:43 ` Greg Kroah-Hartman
2 siblings, 1 reply; 6+ messages in thread
From: Petr Mladek @ 2022-11-18 11:22 UTC (permalink / raw)
To: John Ogness
Cc: Sergey Senozhatsky, Steven Rostedt, Thomas Gleixner,
linux-kernel, Jason Wessel, Daniel Thompson, Douglas Anderson,
Greg Kroah-Hartman, Jiri Slaby, kgdb-bugreport, linux-serial,
linux-fsdevel, Miguel Ojeda, Richard Weinberger, Anton Ivanov,
Johannes Berg, linux-um, Aaron Tomlin, Luis Chamberlain,
Andy Shevchenko, Ilpo Järvinen, Lukas Wunner,
Geert Uytterhoeven, Geert Uytterhoeven, linux-m68k,
Ard Biesheuvel, linux-efi, linuxppc-dev, Krzysztof Kozlowski,
Alim Akhtar, linux-arm-kernel, linux-samsung-soc, Michal Simek,
Peter Zijlstra, Mathias Nyman, linux-usb, David S. Miller,
Eric Dumazet, Jakub Kicinski, Paolo Abeni, netdev, Helge Deller,
Thomas Zimmermann, Javier Martinez Canillas, Juergen Gross,
Boris Ostrovsky, Tom Rix, linux-fbdev, dri-devel
On Wed 2022-11-16 17:27:12, John Ogness wrote:
> 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.
The patchset looks ready for linux-next from my POV.
I am going to push it there right now to get as much testing
as possible before the merge window.
Any review and comments are still appreciate. We could always
take it back if some critical problems are discovered and
can't be solved easily.
Best Regards,
Petr
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH printk v5 00/40] reduce console_lock scope
2022-11-18 11:22 ` [PATCH printk v5 00/40] reduce console_lock scope Petr Mladek
@ 2022-11-18 14:55 ` Petr Mladek
0 siblings, 0 replies; 6+ messages in thread
From: Petr Mladek @ 2022-11-18 14:55 UTC (permalink / raw)
To: John Ogness
Cc: Sergey Senozhatsky, Steven Rostedt, Thomas Gleixner,
linux-kernel, Jason Wessel, Daniel Thompson, Douglas Anderson,
Greg Kroah-Hartman, Jiri Slaby, kgdb-bugreport, linux-serial,
linux-fsdevel, Miguel Ojeda, Richard Weinberger, Anton Ivanov,
Johannes Berg, linux-um, Aaron Tomlin, Luis Chamberlain,
Andy Shevchenko, Ilpo Järvinen, Lukas Wunner,
Geert Uytterhoeven, Geert Uytterhoeven, linux-m68k,
Ard Biesheuvel, linux-efi, linuxppc-dev, Krzysztof Kozlowski,
Alim Akhtar, linux-arm-kernel, linux-samsung-soc, Michal Simek,
Peter Zijlstra, Mathias Nyman, linux-usb, David S. Miller,
Eric Dumazet, Jakub Kicinski, Paolo Abeni, netdev, Helge Deller,
Thomas Zimmermann, Javier Martinez Canillas, Juergen Gross,
Boris Ostrovsky, Tom Rix, linux-fbdev, dri-devel
On Fri 2022-11-18 12:22:58, Petr Mladek wrote:
> On Wed 2022-11-16 17:27:12, John Ogness wrote:
> > 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.
>
> The patchset looks ready for linux-next from my POV.
>
> I am going to push it there right now to get as much testing
> as possible before the merge window.
JFYI, the patchset is committed in printk/linux.git,
branch rework/console-list-lock.
I'll eventually merge it into rework/kthreads. But I wanted to have
it separated until it gets some more testing in linux-next and
eventually some more review.
Best Regards,
Petr
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH printk v5 00/40] reduce console_lock scope
2022-11-16 16:21 [PATCH printk v5 00/40] reduce console_lock scope John Ogness
2022-11-16 16:21 ` [PATCH printk v5 23/40] tty: nfcon: use console_is_registered() John Ogness
2022-11-18 11:22 ` [PATCH printk v5 00/40] reduce console_lock scope Petr Mladek
@ 2022-11-22 16:43 ` Greg Kroah-Hartman
2 siblings, 0 replies; 6+ messages in thread
From: Greg Kroah-Hartman @ 2022-11-22 16:43 UTC (permalink / raw)
To: John Ogness
Cc: Petr Mladek, Sergey Senozhatsky, Steven Rostedt, Thomas Gleixner,
linux-kernel, Jason Wessel, Daniel Thompson, Douglas Anderson,
Jiri Slaby, kgdb-bugreport, linux-serial, linux-fsdevel,
Miguel Ojeda, Richard Weinberger, Anton Ivanov, Johannes Berg,
linux-um, Aaron Tomlin, Luis Chamberlain, Andy Shevchenko,
Ilpo Järvinen, Lukas Wunner, Geert Uytterhoeven,
Geert Uytterhoeven, linux-m68k, Ard Biesheuvel, linux-efi,
linuxppc-dev, Krzysztof Kozlowski, Alim Akhtar, linux-arm-kernel,
linux-samsung-soc, Michal Simek, Peter Zijlstra, Mathias Nyman,
linux-usb, David S. Miller, Eric Dumazet, Jakub Kicinski,
Paolo Abeni, netdev, Helge Deller, Thomas Zimmermann,
Javier Martinez Canillas, Juergen Gross, Boris Ostrovsky,
Tom Rix, linux-fbdev, dri-devel
On Wed, Nov 16, 2022 at 05:27:12PM +0106, John Ogness wrote:
> 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.
>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
^ permalink raw reply [flat|nested] 6+ messages in thread
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2022-11-16 16:21 [PATCH printk v5 00/40] reduce console_lock scope John Ogness
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2022-11-17 8:18 ` Geert Uytterhoeven
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