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

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Message-ID: <5e327822.1c69fb81.80136.dfc1@mx.google.com>
Date:   Wed, 29 Jan 2020 22:30:57 -0800
From:   Stephen Boyd <swboyd@...omium.org>
To:     Kees Cook <keescook@...omium.org>,
        Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
Cc:     Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        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

Quoting Kees Cook (2020-01-27 15:27:33)
> On Thu, Jan 23, 2020 at 09:30:31PM +0530, Sai Prakash Ranjan wrote:
> > 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.
> 
> I agree this patch isn't the solution, but I'm trying to understand
> where better logic could be added. Is the issue that printk sees both
> earlycon and CON_PRINTBUFFER active? Can we add a new CON_* flag that
> means "not actually printing anything"? (Or maybe a new flag for
> non-printing to replace CON_PRINTBUFFER that lets pstore still work?)
> 

This seems to be fixed by commit def97da13651 ("printk: fix
exclusive_console replaying"). I think there's nothing to do.