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    SubjectRe: [RFC][PATCH] printk: do not call console drivers from printk_safe context
    On (04/25/18 16:48), Petr Mladek wrote:
    [..]
    >
    > The above paragraph is not easy to understand. I wonder if the
    > following might be more clear:
    >
    > "Calling console drivers from printk_safe() context does not really
    > make call_console_drivers() any safer. They are never called
    > recursively thanks to console_trylock() in vprintk_emit()."

    Yes, looks good.

    [..]
    > Unfortunately printk_safe context helps only when console_unlock() is
    > called with IRQs disabled. Otherwise, the per-CPU buffer is flushed
    > in every for(;;) cycle.

    Right. I thought about it. If console_unlock() is called with IRQs
    disabled then we postpone flush until we return from console_unlock()
    and enable local IRQs. But then we have printk_safe() flush, which
    uses printk_deferred() -> queue irq_work -> irq work -> console_unlock(),
    so quite likely we still print out printk_safe() buffer from atomic
    context (from irq in this case).

    > So I agree that printk_safe context does not help much. And I fine
    > with this patch.

    Thanks.

    -ss

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