[PATCH printk v8 00/35] wire up write_atomic() printing

[PATCH printk v8 00/35] wire up write_atomic() printing

[John Ogness]

Hi,

This is v8 of a series to wire up the nbcon consoles so that
they actually perform printing using their write_atomic()
callback. v7 is here [0]. For information about the motivation
of the atomic consoles, please read the cover letter of v1 [1].

The main focus of this series:

- For nbcon consoles, always call write_atomic() directly from
  printk() caller context for the panic CPU.

- For nbcon consoles, call write_atomic() when unlocking the
  console lock.

- Only perform the console lock/unlock dance if legacy or boot
  consoles are registered.

- For legacy consoles, if nbcon consoles are registered, do not
  attempt to print from printk() caller context for the panic
  CPU until nbcon consoles have had a chance to print the most
  significant messages.

- Mark emergency sections. In these sections, every printk()
  call will attempt to directly flush to the consoles using the
  EMERGENCY priority.

This series does _not_ include threaded printing or nbcon
drivers. Those features will be added in separate follow-up
series.

The changes since v7:

- Change printk_get_console_flush_type() to set preferred flush
  types.

- Change printk_get_console_flush_type() to also check for
  legacy consoles before seting @legacy_direct.

- Change vprintk_emit() to hack the struct console_flush_type
  for LOGLEVEL_SCHED rather than using local variables.

- Change console_cpu_notify() to also flush nbcon atomic
  consoles.

- Remove unnecessary flush type check in
  nbcon_atomic_flush_pending_con(). It is not needed until the
  threaded series.

- Fix compiling issues related to @legacy_allow_panic_sync for
  !CONFIG_PRINTK.

John Ogness

[0] https://lore.kernel.org/lkml/20240804005138.3722656-1-john.ogness@linutronix.de
[1] https://lore.kernel.org/lkml/20230302195618.156940-1-john.ogness@linutronix.de

John Ogness (30):
  printk: Add notation to console_srcu locking
  printk: nbcon: Consolidate alloc() and init()
  printk: nbcon: Clarify rules of the owner/waiter matching
  printk: nbcon: Remove return value for write_atomic()
  printk: nbcon: Add detailed doc for write_atomic()
  printk: nbcon: Add callbacks to synchronize with driver
  printk: nbcon: Use driver synchronization while (un)registering
  serial: core: Provide low-level functions to lock port
  serial: core: Introduce wrapper to set @uart_port->cons
  console: Improve console_srcu_read_flags() comments
  nbcon: Add API to acquire context for non-printing operations
  serial: core: Acquire nbcon context in port->lock wrapper
  printk: nbcon: Do not rely on proxy headers
  printk: Make console_is_usable() available to nbcon.c
  printk: Let console_is_usable() handle nbcon
  printk: Add @flags argument for console_is_usable()
  printk: nbcon: Add helper to assign priority based on CPU state
  printk: Track registered boot consoles
  printk: nbcon: Use nbcon consoles in console_flush_all()
  printk: Add is_printk_legacy_deferred()
  printk: nbcon: Flush new records on device_release()
  printk: Flush nbcon consoles first on panic
  printk: nbcon: Add unsafe flushing on panic
  printk: Avoid console_lock dance if no legacy or boot consoles
  printk: Track nbcon consoles
  printk: Coordinate direct printing in panic
  printk: Add helper for flush type logic
  panic: Mark emergency section in oops
  rcu: Mark emergency sections in rcu stalls
  lockdep: Mark emergency sections in lockdep splats

Petr Mladek (1):
  printk: Properly deal with nbcon consoles on seq init

Sebastian Andrzej Siewior (1):
  printk: Check printk_deferred_enter()/_exit() usage

Thomas Gleixner (3):
  printk: nbcon: Provide function to flush using write_atomic()
  printk: nbcon: Implement emergency sections
  panic: Mark emergency section in warn

 drivers/tty/serial/8250/8250_core.c |   6 +-
 drivers/tty/serial/amba-pl011.c     |   2 +-
 drivers/tty/serial/serial_core.c    |  16 +-
 include/linux/console.h             | 110 +++++-
 include/linux/printk.h              |  33 +-
 include/linux/serial_core.h         | 117 +++++-
 kernel/locking/lockdep.c            |  83 ++++-
 kernel/panic.c                      |   9 +
 kernel/printk/internal.h            | 137 ++++++-
 kernel/printk/nbcon.c               | 556 +++++++++++++++++++++++++---
 kernel/printk/printk.c              | 251 ++++++++++---
 kernel/printk/printk_ringbuffer.h   |   2 +
 kernel/printk/printk_safe.c         |  23 +-
 kernel/rcu/tree_exp.h               |   7 +
 kernel/rcu/tree_stall.h             |   9 +
 15 files changed, 1210 insertions(+), 151 deletions(-)


base-commit: bcc954c6caba01fca143162d5fbb90e46aa1ad80
-- 
2.39.2

[PATCH printk v8 34/35] rcu: Mark emergency sections in rcu stalls

[John Ogness]

Mark emergency sections wherever multiple lines of
rcu stall information are generated. In an emergency
section, every printk() call will attempt to directly
flush to the consoles using the EMERGENCY priority.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
---
 kernel/rcu/tree_exp.h   | 7 +++++++
 kernel/rcu/tree_stall.h | 9 +++++++++
 2 files changed, 16 insertions(+)

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 4acd29d16fdb..f6b35a0585a8 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -7,6 +7,7 @@
  * Authors: Paul E. McKenney <paulmck@linux.ibm.com>
  */
 
+#include <linux/console.h>
 #include <linux/lockdep.h>
 
 static void rcu_exp_handler(void *unused);
@@ -590,6 +591,9 @@ static void synchronize_rcu_expedited_wait(void)
 			return;
 		if (rcu_stall_is_suppressed())
 			continue;
+
+		nbcon_cpu_emergency_enter();
+
 		j = jiffies;
 		rcu_stall_notifier_call_chain(RCU_STALL_NOTIFY_EXP, (void *)(j - jiffies_start));
 		trace_rcu_stall_warning(rcu_state.name, TPS("ExpeditedStall"));
@@ -643,6 +647,9 @@ static void synchronize_rcu_expedited_wait(void)
 			rcu_exp_print_detail_task_stall_rnp(rnp);
 		}
 		jiffies_stall = 3 * rcu_exp_jiffies_till_stall_check() + 3;
+
+		nbcon_cpu_emergency_exit();
+
 		panic_on_rcu_stall();
 	}
 }
diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index 4b0e9d7c4c68..b3a6943127bc 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -7,6 +7,7 @@
  * Author: Paul E. McKenney <paulmck@linux.ibm.com>
  */
 
+#include <linux/console.h>
 #include <linux/kvm_para.h>
 #include <linux/rcu_notifier.h>
 
@@ -605,6 +606,8 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps)
 	if (rcu_stall_is_suppressed())
 		return;
 
+	nbcon_cpu_emergency_enter();
+
 	/*
 	 * OK, time to rat on our buddy...
 	 * See Documentation/RCU/stallwarn.rst for info on how to debug
@@ -657,6 +660,8 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps)
 	rcu_check_gp_kthread_expired_fqs_timer();
 	rcu_check_gp_kthread_starvation();
 
+	nbcon_cpu_emergency_exit();
+
 	panic_on_rcu_stall();
 
 	rcu_force_quiescent_state();  /* Kick them all. */
@@ -677,6 +682,8 @@ static void print_cpu_stall(unsigned long gps)
 	if (rcu_stall_is_suppressed())
 		return;
 
+	nbcon_cpu_emergency_enter();
+
 	/*
 	 * OK, time to rat on ourselves...
 	 * See Documentation/RCU/stallwarn.rst for info on how to debug
@@ -706,6 +713,8 @@ static void print_cpu_stall(unsigned long gps)
 			   jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
 	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 
+	nbcon_cpu_emergency_exit();
+
 	panic_on_rcu_stall();
 
 	/*
-- 
2.39.2

Re: [PATCH printk v8 34/35] rcu: Mark emergency sections in rcu stalls

[Paul E. McKenney]

On Tue, Aug 20, 2024 at 08:36:00AM +0206, John Ogness wrote:
> Mark emergency sections wherever multiple lines of
> rcu stall information are generated. In an emergency
> section, every printk() call will attempt to directly
> flush to the consoles using the EMERGENCY priority.
> 
> Signed-off-by: John Ogness <john.ogness@linutronix.de>
> Reviewed-by: Petr Mladek <pmladek@suse.com>

I am guessing that this should go with the rest of this series, so:

Acked-by: Paul E. McKenney <paulmck@kernel.org>

> ---
>  kernel/rcu/tree_exp.h   | 7 +++++++
>  kernel/rcu/tree_stall.h | 9 +++++++++
>  2 files changed, 16 insertions(+)
> 
> diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
> index 4acd29d16fdb..f6b35a0585a8 100644
> --- a/kernel/rcu/tree_exp.h
> +++ b/kernel/rcu/tree_exp.h
> @@ -7,6 +7,7 @@
>   * Authors: Paul E. McKenney <paulmck@linux.ibm.com>
>   */
>  
> +#include <linux/console.h>
>  #include <linux/lockdep.h>
>  
>  static void rcu_exp_handler(void *unused);
> @@ -590,6 +591,9 @@ static void synchronize_rcu_expedited_wait(void)
>  			return;
>  		if (rcu_stall_is_suppressed())
>  			continue;
> +
> +		nbcon_cpu_emergency_enter();
> +
>  		j = jiffies;
>  		rcu_stall_notifier_call_chain(RCU_STALL_NOTIFY_EXP, (void *)(j - jiffies_start));
>  		trace_rcu_stall_warning(rcu_state.name, TPS("ExpeditedStall"));
> @@ -643,6 +647,9 @@ static void synchronize_rcu_expedited_wait(void)
>  			rcu_exp_print_detail_task_stall_rnp(rnp);
>  		}
>  		jiffies_stall = 3 * rcu_exp_jiffies_till_stall_check() + 3;
> +
> +		nbcon_cpu_emergency_exit();
> +
>  		panic_on_rcu_stall();
>  	}
>  }
> diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
> index 4b0e9d7c4c68..b3a6943127bc 100644
> --- a/kernel/rcu/tree_stall.h
> +++ b/kernel/rcu/tree_stall.h
> @@ -7,6 +7,7 @@
>   * Author: Paul E. McKenney <paulmck@linux.ibm.com>
>   */
>  
> +#include <linux/console.h>
>  #include <linux/kvm_para.h>
>  #include <linux/rcu_notifier.h>
>  
> @@ -605,6 +606,8 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps)
>  	if (rcu_stall_is_suppressed())
>  		return;
>  
> +	nbcon_cpu_emergency_enter();
> +
>  	/*
>  	 * OK, time to rat on our buddy...
>  	 * See Documentation/RCU/stallwarn.rst for info on how to debug
> @@ -657,6 +660,8 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps)
>  	rcu_check_gp_kthread_expired_fqs_timer();
>  	rcu_check_gp_kthread_starvation();
>  
> +	nbcon_cpu_emergency_exit();
> +
>  	panic_on_rcu_stall();
>  
>  	rcu_force_quiescent_state();  /* Kick them all. */
> @@ -677,6 +682,8 @@ static void print_cpu_stall(unsigned long gps)
>  	if (rcu_stall_is_suppressed())
>  		return;
>  
> +	nbcon_cpu_emergency_enter();
> +
>  	/*
>  	 * OK, time to rat on ourselves...
>  	 * See Documentation/RCU/stallwarn.rst for info on how to debug
> @@ -706,6 +713,8 @@ static void print_cpu_stall(unsigned long gps)
>  			   jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
>  	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
>  
> +	nbcon_cpu_emergency_exit();
> +
>  	panic_on_rcu_stall();
>  
>  	/*
> -- 
> 2.39.2
> 

Re: [PATCH printk v8 00/35] wire up write_atomic() printing

[Petr Mladek]

On Tue 2024-08-20 08:35:26, John Ogness wrote:
> Hi,
> 
> This is v8 of a series to wire up the nbcon consoles so that
> they actually perform printing using their write_atomic()
> callback. v7 is here [0]. For information about the motivation
> of the atomic consoles, please read the cover letter of v1 [1].
> 
> The main focus of this series:
> 
> - For nbcon consoles, always call write_atomic() directly from
>   printk() caller context for the panic CPU.
> 
> - For nbcon consoles, call write_atomic() when unlocking the
>   console lock.
> 
> - Only perform the console lock/unlock dance if legacy or boot
>   consoles are registered.
> 
> - For legacy consoles, if nbcon consoles are registered, do not
>   attempt to print from printk() caller context for the panic
>   CPU until nbcon consoles have had a chance to print the most
>   significant messages.
> 
> - Mark emergency sections. In these sections, every printk()
>   call will attempt to directly flush to the consoles using the
>   EMERGENCY priority.
> 
> This series does _not_ include threaded printing or nbcon
> drivers. Those features will be added in separate follow-up
> series.

The series seems to be ready for linux-next from my POV.

I am going to push it there once I get approval from John about
the proposed update of the commit message for the 30th patch,
see https://lore.kernel.org/r/ZsWvRETyuh1Yq80j@pathway.suse.cz

Best Regards,
Petr

Re: [PATCH printk v8 00/35] wire up write_atomic() printing

[Sebastian Andrzej Siewior]

On 2024-08-21 11:21:41 [+0200], Petr Mladek wrote:
> The series seems to be ready for linux-next from my POV.
> 
> I am going to push it there once I get approval from John about
> the proposed update of the commit message for the 30th patch,
> see https://lore.kernel.org/r/ZsWvRETyuh1Yq80j@pathway.suse.cz

If it is just the commit message, couldn't you push it now to next now
and then simply rebase it with an updated commit message?

> Best Regards,
> Petr

Sebastian

Re: [PATCH printk v8 00/35] wire up write_atomic() printing

[Petr Mladek]

On Wed 2024-08-21 11:28:41, Sebastian Andrzej Siewior wrote:
> On 2024-08-21 11:21:41 [+0200], Petr Mladek wrote:
> > The series seems to be ready for linux-next from my POV.
> > 
> > I am going to push it there once I get approval from John about
> > the proposed update of the commit message for the 30th patch,
> > see https://lore.kernel.org/r/ZsWvRETyuh1Yq80j@pathway.suse.cz
> 
> If it is just the commit message, couldn't you push it now to next now
> and then simply rebase it with an updated commit message?

I see. It seems that John has vacation and can't respond quickly.

OK, I have pushed the patchset into printk/linux.git,
branch rework/write_atomic. It should appear in
the next rebase of linux-next.

Best Regards,
Petr

Re: [PATCH printk v8 00/35] wire up write_atomic() printing

[Sebastian Andrzej Siewior]

On 2024-08-21 16:09:59 [+0200], Petr Mladek wrote:
> I see. It seems that John has vacation and can't respond quickly.
> 
> OK, I have pushed the patchset into printk/linux.git,
> branch rework/write_atomic. It should appear in
> the next rebase of linux-next.

Thank you.

> Best Regards,
> Petr

Sebastian