Messages in this thread | | | Date | Thu, 19 Jul 2007 16:39:20 +0530 | From | "Satyam Sharma" <> | Subject | Re: [PATCH] [14/58] x86_64: Add on_cpu_single |
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Hi Andi,
On 7/19/07, Andi Kleen <ak@suse.de> wrote: > > Call a function on a target CPU but do the right thing when > we're already on that CPU. That's the main difference from > smp_call_function_single > which does the wrong thing in this case (erroring out)
I think this is no longer the case, is it? With KVM updates already merged in latest mainline -git, that modified smp_call_function_single() behaviour ...
> +#ifdef CONFIG_SMP > +/* Similar to smp_call_function_single, but DTRT when we're already > + on the right CPU. */ > +static inline void on_cpu_single(int cpu, void (*func)(void *), void *info) > +{ > + int me = get_cpu(); > + if (cpu == me) { > + func(info); > + put_cpu(); > + } else { > + put_cpu(); > + /* wait is forced on because the me==cpu case above will always wait */ > + smp_call_function_single(cpu, func, info, 0, 1);
In any case, this is unsafe. smp_call_function_single() -- with the old semantics, which is what this patch assumes, obviously -- is quite pointless without its _caller_ disabling preemption around it. So the put_cpu() must come after the smp_call_function_single, otherwise you won't even detect the error that might happen, seeing you're ignoring its return and this wrapper being void-returning.
> + } > +} > +#else > +static inline void on_cpu_single(int cpu, void (*func)(void *), void *info) > +{
WARN_ON(irqs_disabled()); local_irq_disable();
> + func(info);
local_irq_restore();
> +} > +#endif
... for the sake of API / behaviour consistency.
But probably you should just drop this ... with smp_call_function_single's new semantics, I don't see this function growing any users.
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