linux-kernel - Re: [RFC PATCH 2/4] Rename lock_cpu_hotplug to get_online

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Message-ID: <20071017161308.GD6773@localdomain>
Date:	Wed, 17 Oct 2007 11:13:08 -0500
From:	Nathan Lynch <ntl@...ox.com>
To:	Gautham R Shenoy <ego@...ibm.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Rusty Russel <rusty@...tcorp.com.au>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Oleg Nesterov <oleg@...sign.ru>, Ingo Molnar <mingo@...e.hu>,
	Paul E McKenney <paulmck@...ibm.com>
Subject: Re: [RFC PATCH 2/4] Rename lock_cpu_hotplug to get_online_cpus

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.


> 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();
>  }
-
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