linux-kernel - Re: [PATCH] ARM: SMP: prevent use of the console when using idmap

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Date:	Sat, 5 May 2012 17:49:33 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Colin Cross <ccross@...roid.com>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Will Deacon <will.deacon@....com>,
	Marc Zyngier <marc.zyngier@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: SMP: prevent use of the console when using
	idmap_pgd

On Fri, May 04, 2012 at 06:14:02PM -0700, Colin Cross wrote:
> Commit 4e8ee7de227e3ab9a72040b448ad728c5428a042 (ARM: SMP: use
> idmap_pgd for mapping MMU enable during secondary booting)
> switched secondary boot to use idmap_pgd, which is initialized
> during early_initcall, instead of a page table initialized during
> __cpu_up.  This causes idmap_pgd to contain the static mappings
> but be missing all dynamic mappings.
> 
> If a console is registered that creates a dynamic mapping, the
> printk in secondary_start_kernel will trigger a data abort on
> the missing mapping before the exception handlers have been
> initialized, leading to a hang.  Initial boot is not affected
> because no consoles have been registered, and resume is usually
> not affected because the offending console is suspended.
> Onlining a cpu with hotplug triggers the problem.
> 
> A workaround is to the printk in secondary_start_kernel until
> after the page tables have been switched back to init_mm.

I think this is fine.  Please put it in the patch system, thanks.
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