Re: [PATCH 25/45] staging/octeon: Use get/put_online_cpus_atomic() to prevent CPU offline

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Sun, Jun 23, 2013 at 07:13:33PM +0530, Srivatsa S. Bhat wrote:
> Once stop_machine() is gone from the CPU offline path, we won't be able
> to depend on disabling preemption to prevent CPUs from going offline
> from under us.
> 
> Use the get/put_online_cpus_atomic() APIs to prevent CPUs from going
> offline, while invoking from atomic context.
> 
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: devel@driverdev.osuosl.org
> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
> ---
> 
>  drivers/staging/octeon/ethernet-rx.c |    3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/staging/octeon/ethernet-rx.c b/drivers/staging/octeon/ethernet-rx.c
> index 34afc16..8588b4d 100644
> --- a/drivers/staging/octeon/ethernet-rx.c
> +++ b/drivers/staging/octeon/ethernet-rx.c
> @@ -36,6 +36,7 @@
>  #include <linux/prefetch.h>
>  #include <linux/ratelimit.h>
>  #include <linux/smp.h>
> +#include <linux/cpu.h>
>  #include <linux/interrupt.h>
>  #include <net/dst.h>
>  #ifdef CONFIG_XFRM
> @@ -97,6 +98,7 @@ static void cvm_oct_enable_one_cpu(void)
>  		return;
>  
>  	/* ... if a CPU is available, Turn on NAPI polling for that CPU.  */
> +	get_online_cpus_atomic();
>  	for_each_online_cpu(cpu) {
>  		if (!cpu_test_and_set(cpu, core_state.cpu_state)) {
>  			v = smp_call_function_single(cpu, cvm_oct_enable_napi,
> @@ -106,6 +108,7 @@ static void cvm_oct_enable_one_cpu(void)
>  			break;
>  		}
>  	}
> +	put_online_cpus_atomic();

Does this driver really need to be doing this in the first place?  If
so, why?  The majority of network drivers don't, why is this one
"special"?

thanks,

greg k-h