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 v6 15/17] printk: Implement legacy printer kthread for PREEMPT_RT
Date: Wed, 4 Sep 2024 15:40:25 +0200 [thread overview]
Message-ID: <ZthjSaN25qGud8wr@pathway.suse.cz> (raw)
In-Reply-To: <20240904120536.115780-16-john.ogness@linutronix.de>
On Wed 2024-09-04 14:11:34, John Ogness wrote:
> The write() callback of legacy consoles usually makes use of
> spinlocks. This is not permitted with PREEMPT_RT in atomic
> contexts.
>
> For PREEMPT_RT, create a new kthread to handle printing of all
> the legacy consoles (and nbcon consoles if boot consoles are
> registered). This allows legacy consoles to work on PREEMPT_RT
> without requiring modification. (However they will not have
> the reliability properties guaranteed by nbcon atomic
> consoles.)
>
> Use the existing printk_kthreads_check_locked() to start/stop
> the legacy kthread as needed.
>
> Introduce the macro force_legacy_kthread() to query if the
> forced threading of legacy consoles is in effect. Although
> currently only enabled for PREEMPT_RT, this acts as a simple
> mechanism for the future to allow other preemption models to
> easily take advantage of the non-interference property provided
> by the legacy kthread.
>
> When force_legacy_kthread() is true, the legacy kthread
> fulfills the role of the console_flush_type @legacy_offload by
> waking the legacy kthread instead of printing via the
> console_lock in the irq_work. If the legacy kthread is not
> yet available, no legacy printing takes place (unless in
> panic).
>
> If for some reason the legacy kthread fails to create, any
> legacy consoles are unregistered. With force_legacy_kthread(),
> the legacy kthread is a critical component for legacy consoles.
>
> These changes only affect CONFIG_PREEMPT_RT.
>
> Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Best Regards,
Petr
next prev parent reply other threads:[~2024-09-04 13:40 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-09-04 12:05 [PATCH printk v6 00/17] add threaded printing + the rest John Ogness
2024-09-04 12:05 ` [PATCH printk v6 01/17] printk: nbcon: Add function for printers to reacquire ownership John Ogness
2024-09-09 17:27 ` [tip: sched/rt] " tip-bot2 for John Ogness
2024-09-04 12:05 ` [PATCH printk v6 02/17] printk: Fail pr_flush() if before SYSTEM_SCHEDULING John Ogness
2024-09-09 17:27 ` [tip: sched/rt] " tip-bot2 for John Ogness
2024-09-04 12:05 ` [PATCH printk v6 03/17] printk: Flush console on unregister_console() John Ogness
2024-09-09 17:27 ` [tip: sched/rt] " tip-bot2 for John Ogness
2024-09-04 12:05 ` [PATCH printk v6 04/17] printk: nbcon: Add context to usable() and emit() John Ogness
2024-09-09 17:27 ` [tip: sched/rt] " tip-bot2 for John Ogness
2024-09-04 12:05 ` [PATCH printk v6 05/17] printk: nbcon: Init @nbcon_seq to highest possible John Ogness
2024-09-09 17:27 ` [tip: sched/rt] " tip-bot2 for John Ogness
2024-09-04 12:05 ` [PATCH printk v6 06/17] printk: nbcon: Introduce printer kthreads John Ogness
2024-09-09 17:27 ` [tip: sched/rt] " tip-bot2 for Thomas Gleixner
2024-09-04 12:05 ` [PATCH printk v6 07/17] printk: nbcon: Relocate nbcon_atomic_emit_one() John Ogness
2024-09-09 17:27 ` [tip: sched/rt] " tip-bot2 for John Ogness
2024-09-04 12:05 ` [PATCH printk v6 08/17] printk: nbcon: Use thread callback if in task context for legacy John Ogness
2024-09-09 17:27 ` [tip: sched/rt] " tip-bot2 for John Ogness
2024-09-04 12:05 ` [PATCH printk v6 09/17] printk: nbcon: Rely on kthreads for normal operation John Ogness
2024-09-04 13:31 ` Petr Mladek
2024-09-09 17:27 ` [tip: sched/rt] " tip-bot2 for John Ogness
2024-09-04 12:05 ` [PATCH printk v6 10/17] printk: Provide helper for message prepending John Ogness
2024-09-09 17:27 ` [tip: sched/rt] " tip-bot2 for John Ogness
2024-09-04 12:05 ` [PATCH printk v6 11/17] printk: nbcon: Show replay message on takeover John Ogness
2024-09-09 17:27 ` [tip: sched/rt] " tip-bot2 for John Ogness
2024-09-04 12:05 ` [PATCH printk v6 12/17] proc: consoles: Add notation to c_start/c_stop John Ogness
2024-09-09 17:27 ` [tip: sched/rt] " tip-bot2 for John Ogness
2024-09-04 12:05 ` [PATCH printk v6 13/17] proc: Add nbcon support for /proc/consoles John Ogness
2024-09-09 17:27 ` [tip: sched/rt] " tip-bot2 for John Ogness
2024-09-04 12:05 ` [PATCH printk v6 14/17] tty: sysfs: Add nbcon support for 'active' John Ogness
2024-09-09 17:27 ` [tip: sched/rt] " tip-bot2 for John Ogness
2024-09-04 12:05 ` [PATCH printk v6 15/17] printk: Implement legacy printer kthread for PREEMPT_RT John Ogness
2024-09-04 13:40 ` Petr Mladek [this message]
2024-09-09 17:27 ` [tip: sched/rt] " tip-bot2 for John Ogness
2024-09-04 12:05 ` [PATCH printk v6 16/17] printk: nbcon: Assign nice -20 for printing threads John Ogness
2024-09-09 17:27 ` [tip: sched/rt] " tip-bot2 for John Ogness
2024-09-04 12:05 ` [PATCH printk v6 17/17] printk: Avoid false positive lockdep report for legacy printing John Ogness
2024-09-09 17:27 ` [tip: sched/rt] " tip-bot2 for John Ogness
2024-09-04 14:30 ` [PATCH printk v6 00/17] add threaded printing + the rest Petr Mladek
2024-09-04 14:55 ` John Ogness
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