linux-kernel - Re: [PATCH rcu v2] 4/5] rcu-tasks: Move RCU Tasks self-tests to core

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Message-ID: <1c5acc45-24b0-488d-9a93-8d9b187c013c@paulmck-laptop>
Date: Thu, 6 Feb 2025 02:18:38 -0800
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: John Ogness <john.ogness@...utronix.de>, Petr Mladek <pmladek@...e.com>,
	rcu@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-team@...a.com, rostedt@...dmis.org,
	Frederic Weisbecker <frederic@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Alexei Starovoitov <ast@...nel.org>,
	Andrii Nakryiko <andrii@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH rcu v2] 4/5] rcu-tasks: Move RCU Tasks self-tests to
 core_initcall()

On Thu, Feb 06, 2025 at 01:59:00AM -0800, Paul E. McKenney wrote:
> On Thu, Feb 06, 2025 at 10:02:49AM +0100, Sebastian Andrzej Siewior wrote:
> > On 2025-02-05 15:50:14 [-0800], Paul E. McKenney wrote:
> > > diff --git a/include/linux/printk.h b/include/linux/printk.h
> > > index 4217a9f412b2..d658d7e81bef 100644
> > > --- a/include/linux/printk.h
> > > +++ b/include/linux/printk.h
> > > @@ -207,6 +207,7 @@ void printk_legacy_allow_panic_sync(void);
> > >  extern bool nbcon_device_try_acquire(struct console *con);
> > >  extern void nbcon_device_release(struct console *con);
> > >  void nbcon_atomic_flush_unsafe(void);
> > > +bool pr_flush(int timeout_ms, bool reset_on_progress);
> > …
> > > diff --git a/kernel/reboot.c b/kernel/reboot.c
> > > index a701000bab34..a84828d0757b 100644
> > > --- a/kernel/reboot.c
> > > +++ b/kernel/reboot.c
> > > @@ -704,6 +704,7 @@ void kernel_power_off(void)
> > >  	migrate_to_reboot_cpu();
> > >  	syscore_shutdown();
> > >  	pr_emerg("Power down\n");
> > > +	pr_flush(1000, 1);
> > 
> > this could be true instead 1 given that the type is bool
> 
> Good point, and this matches other usage.  Will fix on my next rebase.

And here is the updated commit.  Thoughts?

							Thanx, Paul

------------------------------------------------------------------------

commit 04ccc09a6eb9a50f79c0a0e46fd273b5131b24f1
Author: Paul E. McKenney <paulmck@...nel.org>
Date:   Wed Feb 5 12:27:23 2025 -0800

    printk: Flush console log from kernel_power_off()
    
    Kernels built with CONFIG_PREEMPT_RT=y can lose significant console output
    and shutdown time, which hides shutdown-time RCU issues from rcutorture.
    Therefore, make pr_flush() public and invoke it after then last print
    in kernel_power_off().
    
    [ paulmck: Apply John Ogness feedback. ]
    [ paulmck: Appy Sebastian Andrzej Siewior feedback. ]
    [ paulmck: Apply kernel test robot feedback. ]
    
    Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
    Reviewed-by: John Ogness <john.ogness@...utronix.de>
    Cc: Petr Mladek <pmladek@...e.com>
    Cc: Steven Rostedt <rostedt@...dmis.org>
    Cc: Sergey Senozhatsky <senozhatsky@...omium.org>

diff --git a/include/linux/printk.h b/include/linux/printk.h
index 4217a9f412b2..5b462029d03c 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -207,6 +207,7 @@ void printk_legacy_allow_panic_sync(void);
 extern bool nbcon_device_try_acquire(struct console *con);
 extern void nbcon_device_release(struct console *con);
 void nbcon_atomic_flush_unsafe(void);
+bool pr_flush(int timeout_ms, bool reset_on_progress);
 #else
 static inline __printf(1, 0)
 int vprintk(const char *s, va_list args)
@@ -315,6 +316,11 @@ static inline void nbcon_atomic_flush_unsafe(void)
 {
 }
 
+static inline bool pr_flush(int timeout_ms, bool reset_on_progress)
+{
+	return true;
+}
+
 #endif
 
 bool this_cpu_in_panic(void);
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 80910bc3470c..b9699eaacf19 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2461,7 +2461,6 @@ asmlinkage __visible int _printk(const char *fmt, ...)
 }
 EXPORT_SYMBOL(_printk);
 
-static bool pr_flush(int timeout_ms, bool reset_on_progress);
 static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress);
 
 #else /* CONFIG_PRINTK */
@@ -2474,7 +2473,6 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
 
 static u64 syslog_seq;
 
-static bool pr_flush(int timeout_ms, bool reset_on_progress) { return true; }
 static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress) { return true; }
 
 #endif /* CONFIG_PRINTK */
@@ -4466,7 +4464,7 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
  * Context: Process context. May sleep while acquiring console lock.
  * Return: true if all usable printers are caught up.
  */
-static bool pr_flush(int timeout_ms, bool reset_on_progress)
+bool pr_flush(int timeout_ms, bool reset_on_progress)
 {
 	return __pr_flush(NULL, timeout_ms, reset_on_progress);
 }
diff --git a/kernel/reboot.c b/kernel/reboot.c
index a701000bab34..3ba15b2c4066 100644
--- a/kernel/reboot.c
+++ b/kernel/reboot.c
@@ -704,6 +704,7 @@ void kernel_power_off(void)
 	migrate_to_reboot_cpu();
 	syscore_shutdown();
 	pr_emerg("Power down\n");
+	pr_flush(1000, true);
 	kmsg_dump(KMSG_DUMP_SHUTDOWN);
 	machine_power_off();
 }