linux-kernel - Re: [PATCH] pstore: Fix printing of duplicate boot messages to console

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Date:   Thu, 23 Jan 2020 11:49:50 -0800
From:   Stephen Boyd <swboyd@...omium.org>
To:     Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Kees Cook <keescook@...omium.org>,
        Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        Tony Luck <tony.luck@...el.com>
Cc:     Matthias Kaehlcke <mka@...omium.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org,
        Douglas Anderson <dianders@...omium.org>,
        Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
Subject: Re: [PATCH] pstore: Fix printing of duplicate boot messages to console

Quoting Sai Prakash Ranjan (2020-01-23 08:00:31)
> Since commit f92b070f2dc8 ("printk: Do not miss new messages
> when replaying the log"), CON_PRINTBUFFER flag causes the
> duplicate boot messages to be printed on the console when
> PSTORE_CONSOLE and earlycon (boot console) is enabled.
> Pstore console registers to boot console when earlycon is
> enabled during pstore_register_console as a part of ramoops
> initialization in postcore_initcall and the printk core
> checks for CON_PRINTBUFFER flag and replays the log buffer
> to registered console (in this case pstore console which
> just registered to boot console) causing duplicate messages
> to be printed. Remove the CON_PRINTBUFFER flag from pstore
> console since pstore is not concerned with the printing of
> buffer to console but with writing of the buffer to the
> backend.
> 
> Console log with earlycon and pstore console enabled:
> 
> [    0.008342] Console: colour dummy device 80x25
> [    0.000000] Booting Linux on physical CPU 0x0000000000 [0x51df805e]
> ...
> [    1.244049] hw-breakpoint: found 6 breakpoint and 4 watchpoint registers.
> [    0.000000] Booting Linux on physical CPU 0x0000000000 [0x51df805e]
> 
> Fixes: f92b070f2dc8 ("printk: Do not miss new messages when replaying the log")
> Reported-by: Douglas Anderson <dianders@...omium.org>
> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
> ---

While I like the idea, it seems that this breaks console-ramoops by
removing all the text that is printed in the kernel log before this
console is registered. I reboot and see that
/sys/fs/pstore/console-ramoops-1 starts like this now:

	localhost ~ # cat /sys/fs/pstore/console-ramoops-0
	[    0.943472] printk: console [pstore-1] enabled

Maybe this console can be "special" and not require anything to be
printed out to visible consoles but still get the entire log contents?
Or we should just not worry about it.