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From: Petr Mladek <pmladek@suse.com>
To: John Ogness <john.ogness@linutronix.de>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH printk v1 02/10] printk: rename printk cpulock API and always disable interrupts
Date: Wed, 4 Aug 2021 11:52:49 +0200	[thread overview]
Message-ID: <YQpjcYSxUU0pjZhU@alley> (raw)
In-Reply-To: <20210803131301.5588-3-john.ogness@linutronix.de>

On Tue 2021-08-03 15:18:53, John Ogness wrote:
> The printk cpulock functions use local_irq_disable(). This means that
> hardware interrupts are also disabled on PREEMPT_RT. To make this
> clear, rename the functions to use the raw_ prefix:
> 
>     raw_printk_cpu_lock_irqsave(flags);
>     raw_printk_cpu_unlock_irqrestore(flags);
> 
> Also, these functions were a NOP for !CONFIG_SMP. But for !CONFIG_SMP
> they still need to disable hardware interrupts. So modify them
> appropriately for this.
> 
> Signed-off-by: John Ogness <john.ogness@linutronix.de>
> ---
>  include/linux/printk.h | 30 ++++++++++++++----------------
>  lib/dump_stack.c       |  4 ++--
>  lib/nmi_backtrace.c    |  4 ++--
>  3 files changed, 18 insertions(+), 20 deletions(-)
> 
> diff --git a/include/linux/printk.h b/include/linux/printk.h
> index 259af4f97f50..ac738d1d9934 100644
> --- a/include/linux/printk.h
> +++ b/include/linux/printk.h
> @@ -280,17 +280,22 @@ static inline void dump_stack(void)
>  extern int __printk_cpu_trylock(void);
>  extern void __printk_wait_on_cpu_lock(void);
>  extern void __printk_cpu_unlock(void);
> +#else
> +#define __printk_cpu_trylock()		1
> +#define __printk_wait_on_cpu_lock()
> +#define __printk_cpu_unlock()
> +#endif /* CONFIG_SMP */

IMHO, it is not obvious that

		while (!__printk_cpu_trylock())		\
			__printk_wait_on_cpu_lock();	\

does nothing in the !CONFIG_SMP case. Please, make it more obvious.
I suggest to define:

#ifdef CONFIG_SMP

#define __printk_cpu_lock()				\
	do {						\
		while (!__printk_cpu_trylock())		\
			__printk_wait_on_cpu_lock();	\
	} while (0)

#else

#define __printk_cpu_lock()

#endif

/**
 * raw_printk_cpu_lock_irqsave() - Disable interrupts and acquire the printk
 *                                 cpu-reentrant spinning lock.
 * @flags: Stack-allocated storage for saving local interrupt state,
 *         to be passed to raw_printk_cpu_unlock_irqrestore().
 *
 * If the lock is owned by another CPU, spin until it becomes available.
 */
#define raw_printk_cpu_lock_irqsave(flags)	\
	do {					\
		local_irq_save(flags);		\
		__printk_cpu_lock();		\
	} while (0)


Best Regards,
Petr

  reply	other threads:[~2021-08-04  9:52 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-03 13:12 [PATCH printk v1 00/10] printk: introduce atomic consoles and sync mode John Ogness
2021-08-03 13:12 ` [PATCH printk v1 01/10] printk: relocate printk cpulock functions John Ogness
2021-08-04  9:24   ` Petr Mladek
2021-08-03 13:12 ` [PATCH printk v1 02/10] printk: rename printk cpulock API and always disable interrupts John Ogness
2021-08-04  9:52   ` Petr Mladek [this message]
2021-08-03 13:12 ` [PATCH printk v1 03/10] kgdb: delay roundup if holding printk cpulock John Ogness
2021-08-03 14:25   ` Daniel Thompson
2021-08-03 15:30     ` John Ogness
2021-08-04 11:31       ` Daniel Thompson
2021-08-04 12:12         ` Petr Mladek
2021-08-04 15:04           ` Daniel Thompson
2021-08-05  3:46             ` John Ogness
2021-08-06 12:06               ` Daniel Thompson
2021-08-04 12:31       ` Petr Mladek
2021-08-03 13:12 ` [PATCH printk v1 04/10] printk: relocate printk_delay() John Ogness
2021-08-04 13:07   ` Petr Mladek
2021-08-03 13:12 ` [PATCH printk v1 05/10] printk: call boot_delay_msec() in printk_delay() John Ogness
2021-08-04 13:09   ` Petr Mladek
2021-08-31  1:04   ` Sergey Senozhatsky
2021-08-03 13:12 ` [PATCH printk v1 06/10] printk: use seqcount_latch for console_seq John Ogness
2021-08-05 12:16   ` Petr Mladek
2021-08-05 15:26     ` John Ogness
2021-08-06 15:56       ` Petr Mladek
2021-08-31  3:05         ` Sergey Senozhatsky
2021-08-03 13:12 ` [PATCH printk v1 07/10] console: add write_atomic interface John Ogness
2021-08-03 14:02   ` Andy Shevchenko
2021-08-06 10:56     ` John Ogness
2021-08-06 11:18       ` Andy Shevchenko
2021-08-31  2:55   ` Sergey Senozhatsky
2021-08-03 13:12 ` [PATCH printk v1 08/10] printk: introduce kernel sync mode John Ogness
2021-08-05 17:11   ` Petr Mladek
2021-08-05 21:25     ` John Ogness
2021-08-03 13:13 ` [PATCH printk v1 09/10] kdb: if available, only use atomic consoles for output mirroring John Ogness
2021-08-03 13:13 ` [PATCH printk v1 10/10] serial: 8250: implement write_atomic John Ogness
2021-08-03 14:07   ` Andy Shevchenko
2021-08-05  7:47     ` Jiri Slaby
2021-08-05  8:26       ` John Ogness
2021-08-03 13:52 ` [PATCH printk v1 00/10] printk: introduce atomic consoles and sync mode Andy Shevchenko
2021-08-05 15:47 ` Petr Mladek
2021-08-31  0:33   ` Sergey Senozhatsky

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