[ 155/167] [PATCH] ARM: 7414/1: SMP: prevent use of the console when using idmap_pgd

Ben Hutchings
2012-05-09T06:00:36Z

From: Colin Cross <ccross@android.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@android.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Ben Hutchings <ben@decadent.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