Re: [PATCH rcu v2] 4/5] rcu-tasks: Move RCU Tasks self-tests to core_initcall()
From: "Paul E. McKenney" <paulmck@kernel.org>
Date: 2025-02-05 23:50:14
Also in:
lkml, rcu
Subsystem:
printk, the rest · Maintainers:
Petr Mladek, Linus Torvalds
On Wed, Feb 05, 2025 at 11:37:25PM +0106, John Ogness wrote:
On 2025-02-05, John Ogness [off-list ref] wrote:quoted
quoted
OK, so I don't need to add "if (IS_ENABLED(CONFIG_PREEMPT_RT))" to guard it, then?For !CONFIG_PREEMPT_RT, if there are legacy consoles registered, pr_flush() will additionally perform a blocking lock on the console_lock.Sorry, I was just thinking about the flushing component of pr_flush(). Later in the function it takes the console_lock even for CONFIG_PREEMPT_RT. So please do _not_ have a guard. pr_flush() should never hang on the console_lock during shutdown, but if does, that is something that will need to be debugged and fixed. @pmladek: Looking forward to reading your input on this.
Here is an updated commit, hopefully applying your feedback correctly.
Thanx, Paul
------------------------------------------------------------------------
commit 35679c18b062368855e183ee6712ca5c16145d8c
Author: Paul E. McKenney [off-list ref]
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. ]
Signed-off-by: Paul E. McKenney [off-list ref]
Cc: Petr Mladek [off-list ref]
Cc: Steven Rostedt [off-list ref]
Cc: John Ogness [off-list ref]
Cc: Sergey Senozhatsky [off-list ref]
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); #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 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..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); kmsg_dump(KMSG_DUMP_SHUTDOWN); machine_power_off(); }