Date: Sun, 19 Apr 2015 11:31:13 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Rabin Vincent <rabin@rab.in>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Guenter Roeck <linux@roeck-us.net>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        "Paul E. McKenney" <paulmck@us.ibm.com>
Subject: Re: qemu:arm test failure due to commit 8053871d0f7f (smp: Fix
 smp_call_function_single_async() locking)
Message-ID: <20150419093112.GA6139@gmail.com>
References: <20150418232325.GA22411@roeck-us.net>
 <20150418234050.GA5987@roeck-us.net>
 <CA+55aFz1934X3wu7FdGerwYMJ_BAkrFsajOQFtU3_ogsUX3_eQ@mail.gmail.com>
 <55330B32.4010907@roeck-us.net>
 <20150419033940.GA25145@debian>
 <CA+55aFw4FSja+VBuCYJ7wLXKVRQZ7w6vOUaUJ4B=FXyBmNkrUg@mail.gmail.com>
 <CA+55aFwTMJ7CAtBaL-uGsgVf9-oyGwqLZwz_pwjX=umbS-2CNQ@mail.gmail.com>
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* Linus Torvalds <torvalds@linux-foundation.org> wrote:

> On Sun, Apr 19, 2015 at 4:48 AM, Linus Torvalds
> <torvalds@linux-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@kernel.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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