linux-kernel - Re: [PATCH v7 1/4] lib/percpu-list: Per-cpu list with associated per-cpu locks

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Message-ID: <570E8419.7090909@hpe.com>
Date:	Wed, 13 Apr 2016 13:38:33 -0400
From:	Waiman Long <waiman.long@....com>
To:	Boqun Feng <boqun.feng@...il.com>
CC:	Alexander Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.com>,
	Jeff Layton <jlayton@...chiereds.net>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Tejun Heo <tj@...nel.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	<linux-fsdevel@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Andi Kleen <andi@...stfloor.org>,
	Dave Chinner <dchinner@...hat.com>,
	Scott J Norton <scott.norton@....com>,
	Douglas Hatch <doug.hatch@....com>
Subject: Re: [PATCH v7 1/4] lib/percpu-list: Per-cpu list with associated
 per-cpu locks

On 04/12/2016 10:09 PM, Boqun Feng wrote:
> Hi Waiman,
>
> On Tue, Apr 12, 2016 at 06:54:43PM -0400, Waiman Long wrote:
> [...]
>> +
>> +/*
>> + * Initialize the per-cpu list head
>> + */
>> +int init_pcpu_list_head(struct pcpu_list_head **ppcpu_head)
>> +{
>> +	struct pcpu_list_head *pcpu_head = alloc_percpu(struct pcpu_list_head);
>> +	int cpu;
>> +
>> +	if (!pcpu_head)
>> +		return -ENOMEM;
>> +
>> +	for_each_possible_cpu(cpu) {
>> +		struct pcpu_list_head *head = per_cpu_ptr(pcpu_head, cpu);
>> +
>> +		INIT_LIST_HEAD(&head->list);
>> +		head->lock = __SPIN_LOCK_UNLOCKED(&head->lock);
>> +		lockdep_set_class(&head->lock,&percpu_list_key);
>> +	}
>> +
>> +	*ppcpu_head = pcpu_head;
>> +	return 0;
>> +}
> The first time I looked at this patch, I had a hard time to figure out
> which "struct pcpu_list_head" pointer is pointing to percpu data(the
> pointer could be the parameter for per/this_cpu_ptr()), and which
> pointer is pointing to actual structure. For example, 'pcpu_head' and
> 'head' above are different types of pointers.
>
> So besides improving my code reading skills, I think the following patch
> helps ;-) Also it can resolve several splats of sparse when running
> 'make C=1 lib/'.
>
> Thoughts?

Yes, I think your patch is helpful. I will include your patch in my 
patchset.

Thanks,
Longman