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

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Date:   Fri, 24 Jan 2020 14:18:14 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Kees Cook <keescook@...omium.org>,
        Tony Luck <tony.luck@...el.com>,
        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>
Subject: Re: [PATCH] pstore: Fix printing of duplicate boot messages to
 console

On 2020-01-24 01:19, Stephen Boyd wrote:
> 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.

Thanks for testing this out Stephen, I should have tested this some 
more.
Lets drop this patch.

-Sai

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