linux-kernel - Re: [PATCH v6 2/8] x86: allow to call text_poke

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Date:	Tue, 10 Dec 2013 16:46:12 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Petr Mladek <pmladek@...e.cz>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Jiri Kosina <jkosina@...e.cz>, linux-kernel@...r.kernel.org,
	x86@...nel.org
Subject: Re: [PATCH v6 2/8] x86: allow to call text_poke_bp during boot

On Tue, Dec 10, 2013 at 04:42:14PM +0100, Petr Mladek wrote:
> We would like to use text_poke_bp in ftrace. It might be called also during
> boot when there is only one CPU and we do not need to sync the others.
> 
> The check is must to have because there are also disabled interrupts during
> the boot. Then the call would cause a deadlock, see the warning in
> "smp_call_function_many", kernel/smp.c:371.
> 
> The change is inspired by the code in arch/x86/kernel/ftrace.c.
> 
> Signed-off-by: Petr Mladek <pmladek@...e.cz>
> Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> ---
>  arch/x86/kernel/alternative.c | 17 ++++++++++++++---
>  1 file changed, 14 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
> index eabed9326d2a..6436beec7b0c 100644
> --- a/arch/x86/kernel/alternative.c
> +++ b/arch/x86/kernel/alternative.c
> @@ -599,6 +599,17 @@ static void do_sync_core(void *info)
>  	sync_core();
>  }
>  
> +static void run_sync(void)

Can we call this sync_cores()?

It is what it does. :)

> +{
> +	/*
> +	 * We do not need to sync other cores during boot when there is only one
> +	 * CPU enabled. In fact, we must not because there are also disabled
> +	 * interrupts. The call would fail because of a potential deadlock.
> +	 */
> +	if (num_online_cpus() != 1)
> +		on_each_cpu(do_sync_core, NULL, 1);
> +}

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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