Messages in this thread Patch in this message | | | Date | Sun, 9 Aug 2009 20:39:07 -0700 | From | "Paul E. McKenney" <> | Subject | Re: CONFIG_PREEMPT_RCU in next/mmotm |
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On Sun, Aug 09, 2009 at 02:16:29PM -0700, Paul E. McKenney wrote: > On Sun, Aug 09, 2009 at 09:53:53PM +0100, Hugh Dickins wrote: > > On Sun, 9 Aug 2009, Paul E. McKenney wrote: > > > > > > I introduced the problem in commit 7fe616c5dd50a50f334edec1ea0580b90b7af0d9 > > > by changing from register_cpu_notifier() to hotcpu_notifier(). The former > > > lets you know when CPUs come on line unconditionally, the latter only > > > when CONFIG_HOTPLUG_CPU is in effect. > > > > > > But hotcpu_notifier() is much nicer to use, so I propose introducing > > > a cpu_notifier() that is invoked like hotcpu_notifier() is, but is > > > unconditional in the same way that register_cpu_notifier(). > > > > > > Something like the following (untested, probably does not compile): > > > > > > diff --git a/include/linux/cpu.h b/include/linux/cpu.h > > > index 4d668e0..d5dfc1f 100644 > > > --- a/include/linux/cpu.h > > > +++ b/include/linux/cpu.h > > > @@ -48,6 +48,15 @@ struct notifier_block; > > > > > > #ifdef CONFIG_SMP > > > /* Need to know about CPUs going up/down? */ > > > +#if defined(CONFIG_HOTPLUG_CPU) || !defined(MODULE) > > > +#define cpu_notifier(fn, pri) { \ > > > + static struct notifier_block fn##_nb __cpuinitdata = \ > > > + { .notifier_call = fn, .priority = pri }; \ > > > + register_cpu_notifier(&fn##_nb); \ > > > +} > > > +#else /* #if defined(CONFIG_HOTPLUG_CPU) || !defined(MODULE) */ > > > +#define cpu_notifier(fn, pri) do { (void)(fn); } while (0) > > > +#endif /* #else #if defined(CONFIG_HOTPLUG_CPU) || !defined(MODULE) */ > > > #ifdef CONFIG_HOTPLUG_CPU > > > extern int register_cpu_notifier(struct notifier_block *nb); > > > extern void unregister_cpu_notifier(struct notifier_block *nb); > > > @@ -99,11 +108,7 @@ extern struct sysdev_class cpu_sysdev_class; > > > > > > extern void get_online_cpus(void); > > > extern void put_online_cpus(void); > > > -#define hotcpu_notifier(fn, pri) { \ > > > - static struct notifier_block fn##_nb __cpuinitdata = \ > > > - { .notifier_call = fn, .priority = pri }; \ > > > - register_cpu_notifier(&fn##_nb); \ > > > -} > > > +#define hotcpu_notifier(fn, pri) cpu_notifier(fn, pri) > > > #define register_hotcpu_notifier(nb) register_cpu_notifier(nb) > > > #define unregister_hotcpu_notifier(nb) unregister_cpu_notifier(nb) > > > int cpu_down(unsigned int cpu); > > > diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c > > > index 9f0584e..c1bbfd5 100644 > > > --- a/kernel/rcupdate.c > > > +++ b/kernel/rcupdate.c > > > @@ -251,7 +251,7 @@ void __init rcu_init(void) > > > int i; > > > > > > __rcu_init(); > > > - hotcpu_notifier(rcu_barrier_cpu_hotplug, 0); > > > + cpu_notifier(rcu_barrier_cpu_hotplug, 0); > > > > > > /* > > > * We don't need protection against CPU-hotplug here because > > > > > [ removed repeat of rcupdate.c patch ] > > > > > > Thoughts? > > > > That builds and works for me, with or without CONFIG_HOTPLUG_CPU. > > > > But I didn't get what you're achieving with the MODULE part of it; > > and (I'm not a notifier buff at all) it does seems rather baroque to > > me - a single callsite, why not stick with register_cpu_notifier()? > > > > Ah, perhaps it's your ambition to move others over to this > > (or perhaps it's your ambition to leave that to someone else ;-) > > Actually, nothing quite that clearly thought out. I was just following > the pattern set for register_cpu_notifier(). My guess at the reasoning > is that when !HOTPLUG_CPU, modules cannot be loaded until all the CPUs > are online, so there is no point in letting a module set itself up for > notification. > > But whatever their reasoning, mine was that there is no point in > creating a struct notifier_block that wasn't going to be used. ;-)
And the above patch fails for !CONFIG_SMP. Here is an update, testing in progress. Still not fully tested, but results are encouraging. In particular, this one is more likely to compile.
Thanx, Paul
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diff --git a/include/linux/cpu.h b/include/linux/cpu.h index 4d668e0..4753619 100644 --- a/include/linux/cpu.h +++ b/include/linux/cpu.h @@ -48,6 +48,15 @@ struct notifier_block; #ifdef CONFIG_SMP /* Need to know about CPUs going up/down? */ +#if defined(CONFIG_HOTPLUG_CPU) || !defined(MODULE) +#define cpu_notifier(fn, pri) { \ + static struct notifier_block fn##_nb __cpuinitdata = \ + { .notifier_call = fn, .priority = pri }; \ + register_cpu_notifier(&fn##_nb); \ +} +#else /* #if defined(CONFIG_HOTPLUG_CPU) || !defined(MODULE) */ +#define cpu_notifier(fn, pri) do { (void)(fn); } while (0) +#endif /* #else #if defined(CONFIG_HOTPLUG_CPU) || !defined(MODULE) */ #ifdef CONFIG_HOTPLUG_CPU extern int register_cpu_notifier(struct notifier_block *nb); extern void unregister_cpu_notifier(struct notifier_block *nb); @@ -74,6 +83,8 @@ extern void cpu_maps_update_done(void); #else /* CONFIG_SMP */ +#define cpu_notifier(fn, pri) do { (void)(fn); } while (0) + static inline int register_cpu_notifier(struct notifier_block *nb) { return 0; @@ -99,11 +110,7 @@ extern struct sysdev_class cpu_sysdev_class; extern void get_online_cpus(void); extern void put_online_cpus(void); -#define hotcpu_notifier(fn, pri) { \ - static struct notifier_block fn##_nb __cpuinitdata = \ - { .notifier_call = fn, .priority = pri }; \ - register_cpu_notifier(&fn##_nb); \ -} +#define hotcpu_notifier(fn, pri) cpu_notifier(fn, pri) #define register_hotcpu_notifier(nb) register_cpu_notifier(nb) #define unregister_hotcpu_notifier(nb) unregister_cpu_notifier(nb) int cpu_down(unsigned int cpu); diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c index 9f0584e..c1bbfd5 100644 --- a/kernel/rcupdate.c +++ b/kernel/rcupdate.c @@ -251,7 +251,7 @@ void __init rcu_init(void) int i; __rcu_init(); - hotcpu_notifier(rcu_barrier_cpu_hotplug, 0); + cpu_notifier(rcu_barrier_cpu_hotplug, 0); /* * We don't need protection against CPU-hotplug here because
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