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