linux-kernel - Re: [PATCH 25/45] staging/octeon: Use get/put_online_cpus

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Message-ID: <51C744A9.8000406@linux.vnet.ibm.com>
Date:	Mon, 24 Jun 2013 00:25:37 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:	tglx@...utronix.de, peterz@...radead.org, tj@...nel.org,
	oleg@...hat.com, paulmck@...ux.vnet.ibm.com, rusty@...tcorp.com.au,
	mingo@...nel.org, akpm@...ux-foundation.org, namhyung@...nel.org,
	walken@...gle.com, vincent.guittot@...aro.org,
	laijs@...fujitsu.com, rostedt@...dmis.org,
	wangyun@...ux.vnet.ibm.com, xiaoguangrong@...ux.vnet.ibm.com,
	sbw@....edu, fweisbec@...il.com, zhong@...ux.vnet.ibm.com,
	nikunj@...ux.vnet.ibm.com, linux-pm@...r.kernel.org,
	linux-arch@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	devel@...verdev.osuosl.org, ddaney@...iumnetworks.com
Subject: Re: [PATCH 25/45] staging/octeon: Use get/put_online_cpus_atomic()
 to prevent CPU offline

On 06/23/2013 11:47 PM, Greg Kroah-Hartman wrote:
> 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@...uxfoundation.org>
>> Cc: devel@...verdev.osuosl.org
>> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.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"?
> 

Honestly, I don't know. Let's CC the author of that code (David Daney).
I wonder why get_maintainer.pl didn't generate his name for this file,
even though the entire file is almost made up of his commits alone!

Regards,
Srivatsa S. Bhat

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