linux-kernel - [PATCH RFC] Fix bug if earlyprintk is called twice

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Date:	Thu, 18 Apr 2013 16:23:38 +0200
From:	Gregory CLEMENT <gregory.clement@...e-electrons.com>
To:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Russell King <linux@....linux.org.uk>
Cc:	Kay Sievers <kay@...y.org>,
	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Lior Amsalem <alior@...vell.com>,
	Gregory CLEMENT <gregory.clement@...e-electrons.com>
Subject: [PATCH RFC] Fix bug if earlyprintk is called twice

Hello,

If on the kernel command line the parameter "earlyprintk" is written
twice, then setup_early_printk is called twice. This can happen for
example with the option CONFIG_ARM_ATAG_DTB_COMPAT_CMDLINE_EXTEND is
selected, and the "earlyprintk" is passed from the ATAG_CMDLINE and
from the dtb.

This lead to an infinite loop on the message "Booting Linux on
physical CPU 0" displayed from smp_setup_processor_id() in
arch/arm/kernel/setup.c. This behavior as been reproduced on ARMv7
architecture (Armada XP and Armada 370), and on a ARMv5 one
(AT91SAMG35 thanks to Richard Genoud), with and with CONFIG_SMP
selected.

After some investigation I found that the problem happened when the
early_console is register for the second time in file kernel/printk.c
on line 2310 when the function console_lock() is called, and in this
function I managed to have traces until the call to down(&console_sem)
one line 1922. Keep in mind that I had this information using printk
so maybe it was not the best way to debug the console!

I didn't had other platform that ARM one for testing this behavior, so
I don't know if this bug is specific to ARM. If you think it is
something specific to ARM then I propose the patch in the following
email.

Any feedback on this issue would be welcome

Thanks,

Gregory CLEMENT (1):
  ARM: don't allow to register the early_console twice

 arch/arm/kernel/early_printk.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

-- 
1.7.9.5

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