[PATCH] ARM: SMP: prevent use of the console when using idmap_pgd

* [PATCH] ARM: SMP: prevent use of the console when using idmap_pgd
@ 2012-05-05  1:14 Colin Cross
  2012-05-05 16:49 ` Russell King - ARM Linux
  2012-05-08  9:21 ` Will Deacon
  0 siblings, 2 replies; 5+ messages in thread
From: Colin Cross @ 2012-05-05  1:14 UTC (permalink / raw)
  To: linux-arm-kernel
  Cc: Colin Cross, Russell King, Will Deacon, Marc Zyngier,
	Catalin Marinas, Thomas Gleixner, linux-kernel

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@android.com>
---
 arch/arm/kernel/smp.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index addbbe8..aa98928 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();
-- 
1.7.7.3


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