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SubjectRe: [PATCH 3/3] early_printk: Add simple serialization to early_vprintk()
On Tue, 18 Oct 2016 19:08:33 +0200
Peter Zijlstra <peterz@infradead.org> wrote:

> In order to avoid multiple CPUs banging on the serial port at the same
> time, add simple serialization. This explicitly deals with nested
> contexts (like IRQs etc.).
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---

hehe, I have the exact same patch for my -rt work.

-- Steve

> kernel/printk/printk.c | 16 +++++++++++++++-
> 1 file changed, 15 insertions(+), 1 deletion(-)
>
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -356,14 +356,28 @@ static int __init force_early_printk_set
> }
> early_param("force_early_printk", force_early_printk_setup);
>
> +static int early_printk_cpu = -1;
> +
> static int early_vprintk(const char *fmt, va_list args)
> {
> + int n, cpu, old;
> char buf[512];
> - int n;
> +
> + cpu = get_cpu();
> + for (;;) {
> + old = cmpxchg(&early_printk_cpu, -1, cpu);
> + if (old == -1 || old == cpu)
> + break;
> +
> + cpu_relax();
> + }
>
> n = vscnprintf(buf, sizeof(buf), fmt, args);
> early_console->write(early_console, buf, n);
>
> + smp_store_release(&early_printk_cpu, old);
> + put_cpu();
> +
> return n;
> }
>
>

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