linux-kernel - Re: [PATCH 4.19 regression fix] printk: For early boot messages check loglevel when flushing the buffer

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Message-ID: <20180906072940.GA382@jagdpanzerIV>
Date:   Thu, 6 Sep 2018 16:29:40 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        Steven Rostedt <rostedt@...dmis.org>,
        Maninder Singh <maninder1.s@...sung.com>
Subject: Re: [PATCH 4.19 regression fix] printk: For early boot messages
 check loglevel when flushing the buffer

On (09/05/18 13:02), Petr Mladek wrote:
> Note that the first registered console prints all messages
> even without this flag.

Hmm, OK, interesting point.

I assumed that the first console usually has CON_PRINTBUFFER bit set.
Or even a CON_PRINTBUFFER | CON_ANYTIME combo. E.g. 8250. It sort of
makes sense to have CON_PRINTBUFFER for the first console. Any later
consoles [e.g. fbcon, netcon] don't necessarily have CON_PRINTBUFFER.

So by the time we have callable console "quite" param should be already
parsed [except the earlycon case perhaps]:

	kernel_init_freeable
	 do_one_initcall
	  register_console
happens after
	setup_arch
	 parse_early_param
	  quiet_kernel/debug_kernel.

And
	setup_arch
	 parse_early_param
	  quiet_kernel/debug_kernel
happens before
	console_init
	 con_init
	  register_console.

And the first console has CON_PRINTBUFFER bit set. Well, just because
it sounds reasonable. Those were the main assumptions behind my code
snippet. Was any of those assumptions wrong?

> I played with another solution, see the patch below. It defines
> which messages have a valid NOCONS flag according to the msg_seq
> number. IMHO, it is a bit more straightforward but it is still
> a hack. I am not super happy about it.

I just skimmed through it, and probably missed some parts. But I sort
of expected to see some console_valid_nocons_seq manipulations in
register_console(), when we register a new CON_PRINTBUFFER console
on already running system.

> Hmm, I seriously think about reverting the commit 375899cddcbb
> ("printk: make sure to print log on console.") and solving it
> another way.

I can agree, definitely. That's one of the options.

	-ss