On 6/7/07, Heiko Carstens <[email protected]> wrote:
[...]
> Avi Kivity has already a patch which introduces an on_cpu() function which
> looks quite like on_each_cpu(). That way you don't have to open code this
> stuff over and over again:
>
> preempt_disable();
> if (cpu == smp_processor_id())
> func();
> else
> smp_call_function_single(...);
> preempt_enable();
>
> There are already quite a few of these around.
Indeed -- this was doubly problematic because the un-safeness
was because of smp_processor_id() as well as the (eventual)
access of cpu_online_map (via smp_call_function() ->
num_online_cpus()) ... thanks for letting me know about this.
Oh wait, the on_one_cpu() patch proposes on UP:
+static inline int on_one_cpu(int cpu, void (*func)(void *info), void *info,
+ int retry, int wait)
+{
/* this needs a if (cpu == 0) check here, IMO */
+ local_irq_disable();
+ func(info);
+ local_irq_enable();
+ return 0;
/* else WARN and return -EINVAL; */
+}
which is broken without the suggested additions, IMHO
(this is what got me into this in the first place). There
_is_ a difference between on_each_cpu() and the
smp_call_function* semantics (as discussed on the other
thread -- gargh! my mistake for opening this discussion up
on so many threads), and in its current form on_one_cpu()
has quite confused semantics, trying to mix the two. I guess
on_one_cpu() would be better off simply being just an
atomic wrapper over smp_processor_id() and
smp_call_function_single() (which is the *real* issue that
needs solving in the first place), and do it well.
Satyam
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