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 09/17] printk: nbcon: Rely on kthreads for normal operation
Date: Wed, 4 Sep 2024 15:31:10 +0200 [thread overview]
Message-ID: <ZthhHrESqU9KFXrz@pathway.suse.cz> (raw)
In-Reply-To: <20240904120536.115780-10-john.ogness@linutronix.de>
On Wed 2024-09-04 14:11:28, John Ogness wrote:
> Once the kthread is running and available
> (i.e. @printk_kthreads_running is set), the kthread becomes
> responsible for flushing any pending messages which are added
> in NBCON_PRIO_NORMAL context. Namely the legacy
> console_flush_all() and device_release() no longer flush the
> console. And nbcon_atomic_flush_pending() used by
> nbcon_cpu_emergency_exit() no longer flushes messages added
> after the emergency messages.
>
> The console context is safe when used by the kthread only when
> one of the following conditions are true:
>
> 1. Other caller acquires the console context with
> NBCON_PRIO_NORMAL with preemption disabled. It will
> release the context before rescheduling.
>
> 2. Other caller acquires the console context with
> NBCON_PRIO_NORMAL under the device_lock.
>
> 3. The kthread is the only context which acquires the console
> with NBCON_PRIO_NORMAL.
>
> This is satisfied for all atomic printing call sites:
>
> nbcon_legacy_emit_next_record() (#1)
>
> nbcon_atomic_flush_pending_con() (#1)
>
> nbcon_device_release() (#2)
>
> It is even double guaranteed when @printk_kthreads_running
> is set because then _only_ the kthread will print for
> NBCON_PRIO_NORMAL. (#3)
>
> 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 13:31 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 [this message]
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
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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