Hi Andrew,
> >
> > Usage:
> > a) Each hotcpu aware subsystem defines the hotcpu_mutex as follows
> > #ifdef CONFIG_HOTPLUG_CPU
> > DEFINE_MUTEX(my_hotcpu_mutex);
> > #endif
> >
> > b) The hotcpu aware subsystem uses
> > cpuhotplug_mutex_lock(&my_hotcpu_mutex)
> > and
> > cpuhotplug_mutex_unlock(&my_hotcpu_mutex)
> > instead of the usual mutex_lock/mutex_unlock.
> >
> > Signed-off-by: Gautham R Shenoy <[email protected]>
> >
> > ---
> > include/linux/cpu.h | 15 +++++++++++++++
[snip]
> > extern void unlock_cpu_hotplug(void);
> > #define hotcpu_notifier(fn, pri) { \
> > @@ -86,6 +98,9 @@ extern void unlock_cpu_hotplug(void);
> > int cpu_down(unsigned int cpu);
> > #define cpu_is_offline(cpu) unlikely(!cpu_online(cpu))
> > #else
> > +#define cpuhotplug_mutex_lock(m) do { } while (0)
> > +#define cpuhotplug_mutex_unlock(m) do { } while (0)
> > +
>
> But what to do about the now-unneeded mutex?
>
> We can just leave it there if CONFIG_HOTPLUG_CPU=n but then we'll get
> unused variable warnings for statically-defined mutexes.
Why even leave it there?
Can't we do something as follows, which has already been suggested in
the patch description:
Each hotcpu aware subsystem defines the hotcpu_mutex as follows
#ifdef CONFIG_HOTPLUG_CPU
[static] DEFINE_MUTEX(my_hotcpu_mutex);
#endif
That way, we won't be having any unneeded mutexes at all.
> To fix that would require either
>
> #ifdef CONFIG_HOTPLUG_CPU
> #define DEFINE_MUTEX_HOTPLUG_CPU(m) DEFINE_MUTEX(m)
> #else
> #define DEFINE_MUTEX_HOTPLUG_CPU(m)
> #endif
>
Yup, this won't work. Wish we could cook up something like this, but
alas! Most of these mutexes are defined with the static keyword,
which causes compile errors with CONFIG_HOTPLUG_CPU=n.
> or
>
> #define cpuhotplug_mutex_lock(m) do { (void)(m); } while (0)
>
>
> Given that the former won't work, I'd suggest the latter ;)
>
regards
gautham.
--
Gautham R Shenoy
Linux Technology Center
IBM India.
"Freedom comes with a price tag of responsibility, which is still a bargain,
because Freedom is priceless!"
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