linux-kernel - [ 155/167] [PATCH] ARM: 7414/1: SMP: prevent use of the console when using idmap

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Date:	Wed, 09 May 2012 06:53:04 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Colin Cross <ccross@...roid.com>,
	Russell King <rmk+kernel@....linux.org.uk>
Subject: [ 155/167] [PATCH] ARM: 7414/1: SMP: prevent use of the console when using
 idmap_pgd

3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Colin Cross <ccross@...roid.com>

commit fde165b2a29673aabf18ceff14dea1f1cfb0daad upstream.

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.

Signed-off-by: Colin Cross <ccross@...roid.com>
Signed-off-by: Russell King <rmk+kernel@....linux.org.uk>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/arm/kernel/smp.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index f6a4d32..8f46446 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -251,8 +251,6 @@ asmlinkage void __cpuinit secondary_start_kernel(void)
 	struct mm_struct *mm = &init_mm;
 	unsigned int cpu = smp_processor_id();

-	printk("CPU%u: Booted secondary processor\n", cpu);
-
 	/*
 	 * All kernel threads share the same mm context; grab a
 	 * reference and switch to it.
@@ -264,6 +262,8 @@ asmlinkage void __cpuinit secondary_start_kernel(void)
 	enter_lazy_tlb(mm, current);
 	local_flush_tlb_all();

+	printk("CPU%u: Booted secondary processor\n", cpu);
+
 	cpu_init();
 	preempt_disable();
 	trace_hardirqs_off();
-- 
1.7.10

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