ARM: 7414/1: SMP: prevent use of the console when using idmap_pgd

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.

Cc: <stable@vger.kernel.org>
Signed-off-by: Colin Cross <ccross@android.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 2 insertions, 2 deletions

diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index f6a4d32b0421..8f4644659777 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();