Hi Nathan,
> Hi Gautham-
>
> Gautham R Shenoy wrote:
> > Replace all lock_cpu_hotplug/unlock_cpu_hotplug from the kernel and use
> > get_online_cpus and put_online_cpus instead as it highlights
> > the refcount semantics in these operations.
>
> Something other than "get_online_cpus", please? lock_cpu_hotplug()
> protects cpu_present_map as well as cpu_online_map. For example, some
> of the powerpc code modified in this patch is made a bit less clear
> because it is manipulating cpu_present_map, not cpu_online_map.
A quick look at the code, and I am wondering why is lock_cpu_hotplug()
used there in the first place. It doesn't look like we require any
protection against cpus coming up/ going down in the code below,
since the cpu-hotplug operation doesn't affect the cpu_present_map.
Can't we use another mutex here instead of the cpu_hotplug mutex here ?
>
>
> > Index: linux-2.6.23/arch/powerpc/platforms/pseries/hotplug-cpu.c
> > ===================================================================
> > --- linux-2.6.23.orig/arch/powerpc/platforms/pseries/hotplug-cpu.c
> > +++ linux-2.6.23/arch/powerpc/platforms/pseries/hotplug-cpu.c
> > @@ -151,7 +151,7 @@ static int pseries_add_processor(struct
> > for (i = 0; i < nthreads; i++)
> > cpu_set(i, tmp);
> >
> > - lock_cpu_hotplug();
> > + get_online_cpus();
> >
> > BUG_ON(!cpus_subset(cpu_present_map, cpu_possible_map));
> >
> > @@ -188,7 +188,7 @@ static int pseries_add_processor(struct
> > }
> > err = 0;
> > out_unlock:
> > - unlock_cpu_hotplug();
> > + put_online_cpus();
> > return err;
> > }
> >
> > @@ -209,7 +209,7 @@ static void pseries_remove_processor(str
> >
> > nthreads = len / sizeof(u32);
> >
> > - lock_cpu_hotplug();
> > + get_online_cpus();
> > for (i = 0; i < nthreads; i++) {
> > for_each_present_cpu(cpu) {
> > if (get_hard_smp_processor_id(cpu) != intserv[i])
> > @@ -223,7 +223,7 @@ static void pseries_remove_processor(str
> > printk(KERN_WARNING "Could not find cpu to remove "
> > "with physical id 0x%x\n", intserv[i]);
> > }
> > - unlock_cpu_hotplug();
> > + put_online_cpus();
> > }
--
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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