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
Subject: Re: [PATCH printk v2 06/11] printk: nbcon: Wire up nbcon console atomic flushing
Date: Thu, 05 Oct 2023 16:05:27 +0206 [thread overview]
Message-ID: <87edi9tbk0.fsf@jogness.linutronix.de> (raw)
In-Reply-To: <ZRLLNh4g_BiwxIsA@alley>
On 2023-09-26, Petr Mladek <pmladek@suse.com> wrote:
> Anyway, the proposed behavior (agreed on LPC2022) seems
> to contradict the original plan from LPC 2019, see
> https://lore.kernel.org/all/87k1acz5rx.fsf@linutronix.de/
> Namely:
>
> --- cut ---
> 3. Rather than defining emergency _messages_, we define an emergency
> _state_ where the kernel wants to flush the messages immediately before
> dying. Unlike oops_in_progress, this state will not be visible to
> anything outside of the printk infrastructure.
>
> 4. When in emergency state, the kernel will use a new console callback
> write_atomic() to flush the messages in whatever context the CPU is in
> at that moment. Only consoles that implement the NMI-safe write_atomic()
> will be able to flush in this state.
> --- cut ---
>
> We wanted to flush it ASAP.
In 2019 we didn't have all the code yet. Yes, we assumed that flushing
each individual printk() call would be how to do it. But in 2022, during
a live demo with real code, we saw that it was a bad idea.
I disagree that the 2022 decisions are contradicting the 2019
decisions. We have added more details because now we have a real
implementation.
v2 establishes an emergency state before dying. v2 flushes the messages
safely before dying (and unsafely _immediately_ before dying). v2
flushes the messages in whatever context the CPU is in. v2 uses
write_atomic() to perform the flush.
John
next prev parent reply other threads:[~2023-10-05 14:37 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-19 23:08 [PATCH printk v2 00/11] wire up nbcon atomic printing John Ogness
2023-09-19 23:08 ` [PATCH printk v2 01/11] printk: Make console_is_usable() available to nbcon John Ogness
2023-09-22 8:33 ` Petr Mladek
2023-09-19 23:08 ` [PATCH printk v2 02/11] printk: Let console_is_usable() handle nbcon John Ogness
2023-09-22 8:37 ` Petr Mladek
2023-09-19 23:08 ` [PATCH printk v2 03/11] printk: Add @flags argument for console_is_usable() John Ogness
2023-09-22 8:41 ` Petr Mladek
2023-09-19 23:08 ` [PATCH printk v2 04/11] printk: nbcon: Provide functions to mark atomic write sections John Ogness
2023-09-22 9:33 ` Petr Mladek
2023-09-25 9:25 ` John Ogness
2023-09-25 16:04 ` Petr Mladek
2023-10-05 12:51 ` John Ogness
2023-10-06 12:51 ` panic context: was: " Petr Mladek
2023-10-06 12:53 ` Petr Mladek
2023-10-08 10:13 ` John Ogness
2023-10-09 15:32 ` Petr Mladek
2023-10-10 16:02 ` John Ogness
2023-10-16 8:58 ` Dave Young
2023-10-16 10:09 ` John Ogness
2023-10-06 15:52 ` Petr Mladek
2023-09-19 23:08 ` [PATCH printk v2 05/11] printk: nbcon: Provide function for atomic flushing John Ogness
2023-09-22 12:32 ` Petr Mladek
2023-09-25 11:11 ` John Ogness
2023-09-19 23:08 ` [PATCH printk v2 06/11] printk: nbcon: Wire up nbcon console " John Ogness
2023-09-22 17:41 ` Petr Mladek
2023-09-25 13:37 ` John Ogness
2023-09-26 12:14 ` Petr Mladek
2023-10-05 13:59 ` John Ogness [this message]
2023-09-19 23:08 ` [PATCH printk v2 07/11] printk: nbcon: Wire up nbcon into console_flush_all() John Ogness
2023-09-26 11:34 ` Petr Mladek
2023-09-19 23:08 ` [PATCH printk v2 08/11] panic: Add atomic write enforcement to warn/panic John Ogness
2023-09-27 12:02 ` Petr Mladek
2023-09-19 23:08 ` [PATCH printk v2 09/11] panic: Add atomic write enforcement to oops John Ogness
2023-09-19 23:36 ` John Ogness
2023-09-20 13:28 ` Andy Shevchenko
2023-09-20 14:20 ` John Ogness
2023-09-20 14:45 ` Andy Shevchenko
2023-09-27 13:15 ` Petr Mladek
2023-09-19 23:08 ` [PATCH printk v2 10/11] rcu: Add atomic write enforcement for rcu stalls John Ogness
2023-09-27 15:00 ` Petr Mladek
2023-09-19 23:08 ` [PATCH printk v2 11/11] lockdep: Add atomic write enforcement for lockdep splats John Ogness
2023-09-29 8:31 ` Petr Mladek
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