linux-kernel - Re: qemu:arm test failure due to commit 8053871d0f7f (smp: Fix smp_call_function_single

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Date:	Sun, 19 Apr 2015 11:31:13 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Rabin Vincent <rabin@....in>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Guenter Roeck <linux@...ck-us.net>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Paul E. McKenney" <paulmck@...ibm.com>
Subject: Re: qemu:arm test failure due to commit 8053871d0f7f (smp: Fix
 smp_call_function_single_async() locking)


* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Sun, Apr 19, 2015 at 4:48 AM, Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
> >
> > Does that smaller patch work equally well?
> 
> .. and here's a properly formatted email and patch.
> 
>            Linus

>  kernel/smp.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/smp.c b/kernel/smp.c
> index 2aaac2c47683..07854477c164 100644
> --- a/kernel/smp.c
> +++ b/kernel/smp.c
> @@ -159,8 +159,10 @@ static int generic_exec_single(int cpu, struct call_single_data *csd,
>  	}
>  
>  
> -	if ((unsigned)cpu >= nr_cpu_ids || !cpu_online(cpu))
> +	if ((unsigned)cpu >= nr_cpu_ids || !cpu_online(cpu)) {
> +		csd_unlock(csd);
>  		return -ENXIO;
> +	}

Acked-by: Ingo Molnar <mingo@...nel.org>

Btw., in this case we should probably also generate a WARN_ONCE() 
warning?

I _think_ most such callers calling an SMP function call for offline 
or out of range CPUs are at minimum racy.

Thanks,

	Ingo
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