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From: John Ogness <john.ogness@linutronix.de>
To: Petr Mladek <pmladek@suse.com>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-kernel@vger.kernel.org,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: two locations: was: Re: [PATCH printk v1 03/13] printk: use percpu flag instead of cpu_online()
Date: Mon, 07 Mar 2022 11:12:15 +0106	[thread overview]
Message-ID: <87mti22i20.fsf@jogness.linutronix.de> (raw)
In-Reply-To: <YiI61ppIW+FsrzPu@alley>

On 2022-03-04, Petr Mladek <pmladek@suse.com> wrote:
>> If the context is preemptible, I do not think it will ever see
>> !cpu_online(). So I think if the cpu_online() check is limited to
>> unlocking when console_trylock() was used, it will be correct.
>
> This would require calling console_lock()/console_unlock()
> in a hotplug code when cpu_online() already returns false.
> Do I get it correctly?

Yes, but there is also the other side: Are there preemptible code paths
that are calling console_trylock()? And if yes, then why are they not
using console_lock()?

There is only a handfull of console_trylock() users (about 10
sites). Most of them appear to be differentiating from preemptible and
non-preemptible contexts. I will investigate them in detail.

If the raw_smp_processor_id() is changed to smp_processor_id() within
the console_trylock()/console_unlock() call path, then at least the
kernel's lock debugging would identify if there are preemptible contexts
that are using console_trylock().

John

  reply	other threads:[~2022-03-07 10:45 UTC|newest]

Thread overview: 87+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-02-07 19:43 [PATCH printk v1 00/13] implement threaded console printing John Ogness
2022-02-07 19:43 ` [PATCH printk v1 01/13] printk: rename cpulock functions John Ogness
2022-02-11 12:44   ` Petr Mladek
2022-02-11 14:42     ` John Ogness
2022-02-11 20:57       ` Steven Rostedt
2022-02-11 21:04         ` Peter Zijlstra
2022-02-15  9:32           ` Petr Mladek
2022-02-15  9:13       ` Petr Mladek
2022-02-14  6:49     ` Sergey Senozhatsky
2022-02-14  9:45       ` John Ogness
2022-02-15  9:29       ` Petr Mladek
2022-02-16  3:27         ` Sergey Senozhatsky
2022-02-17 14:34         ` John Ogness
2022-02-07 19:43 ` [PATCH printk v1 02/13] printk: cpu sync always disable interrupts John Ogness
2022-02-11 12:58   ` Petr Mladek
2022-02-14  6:36     ` Sergey Senozhatsky
2022-02-07 19:43 ` [PATCH printk v1 03/13] printk: use percpu flag instead of cpu_online() John Ogness
2022-02-11 16:05   ` Petr Mladek
2022-02-14  7:08     ` Sergey Senozhatsky
2022-02-14  7:35     ` Sergey Senozhatsky
2022-02-15 10:38       ` Petr Mladek
2022-02-16  3:29         ` Sergey Senozhatsky
2022-03-02 14:21         ` John Ogness
2022-03-04 15:56           ` Petr Mladek
2022-03-05 17:05             ` Jason A. Donenfeld
2022-03-07 16:14               ` Petr Mladek
2022-02-16 13:58   ` two locations: was: " Petr Mladek
2022-03-02 14:49     ` John Ogness
2022-03-04 16:14       ` Petr Mladek
2022-03-07 10:06         ` John Ogness [this message]
2022-03-08 16:08       ` Petr Mladek
2022-02-07 19:43 ` [PATCH printk v1 04/13] printk: get caller_id/timestamp after migration disable John Ogness
2022-02-15  5:53   ` Sergey Senozhatsky
2022-02-15 11:56   ` Petr Mladek
2022-02-07 19:43 ` [PATCH printk v1 05/13] printk: call boot_delay_msec() in printk_delay() John Ogness
2022-02-15  5:58   ` Sergey Senozhatsky
2022-02-15 14:59     ` Petr Mladek
2022-02-16  3:21       ` Sergey Senozhatsky
2022-02-15 15:03   ` Petr Mladek
2022-02-07 19:43 ` [PATCH printk v1 06/13] printk: refactor and rework printing logic John Ogness
2022-02-16 15:43   ` Petr Mladek
2022-03-02 16:10     ` John Ogness
2022-02-07 19:43 ` [PATCH printk v1 07/13] printk: move buffer definitions into console_emit_next_record() caller John Ogness
2022-02-16 16:10   ` Petr Mladek
2022-03-02 16:25     ` John Ogness
2022-02-07 19:43 ` [PATCH printk v1 08/13] printk: add pr_flush() John Ogness
2022-02-17 10:11   ` Petr Mladek
2022-03-02 17:23     ` John Ogness
2022-03-04 13:24       ` Petr Mladek
2022-02-07 19:43 ` [PATCH printk v1 09/13] printk: add functions to allow direct printing John Ogness
2022-02-17 12:52   ` Petr Mladek
2022-02-18  9:00     ` David Laight
2022-02-18 12:52       ` Petr Mladek
2022-03-03 14:37     ` John Ogness
2022-02-07 19:43 ` [PATCH printk v1 10/13] printk: add kthread console printers John Ogness
2022-02-18  9:00   ` early start: was: " Petr Mladek
2022-02-18  9:04   ` start&stop: " Petr Mladek
2022-02-18  9:08   ` main loop: " Petr Mladek
2022-02-18  9:12   ` wake_up_all: " Petr Mladek
2022-02-07 19:43 ` [PATCH printk v1 11/13] printk: reimplement console_lock for proper kthread support John Ogness
2022-02-18 16:20   ` Petr Mladek
2022-02-18 21:41     ` John Ogness
2022-02-18 22:03       ` John Ogness
2022-02-22 11:42       ` Petr Mladek
2022-02-23 17:20         ` John Ogness
2022-02-24  8:27           ` Petr Mladek
2022-02-23 10:19   ` Petr Mladek
2022-03-09 13:56     ` John Ogness
2022-03-10 14:34       ` Petr Mladek
2022-03-10 16:08         ` John Ogness
2022-03-11 10:26           ` Petr Mladek
2022-03-11 13:28             ` John Ogness
2022-03-11 16:17               ` Petr Mladek
2022-03-11 22:21                 ` John Ogness
2022-03-14 14:08                   ` Petr Mladek
2022-03-14 14:43                     ` John Ogness
2022-03-14 15:53                       ` Petr Mladek
2022-03-11 18:41               ` Petr Mladek
2022-02-07 19:43 ` [PATCH printk v1 12/13] printk: remove @console_locked John Ogness
2022-02-23 12:17   ` Petr Mladek
2022-02-07 19:43 ` [PATCH printk v1 13/13] console: introduce CON_MIGHT_SLEEP for vt John Ogness
2022-02-23 13:37   ` Petr Mladek
2022-02-23 18:31     ` Greg Kroah-Hartman
     [not found] ` <20220208083620.2736-1-hdanton@sina.com>
2022-02-08 11:08   ` [PATCH printk v1 10/13] printk: add kthread console printers John Ogness
2022-02-08 14:53     ` Petr Mladek
2022-02-14  6:12       ` Sergey Senozhatsky
2022-02-14 10:02         ` Petr Mladek

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