Re: [PATCH 2/5] mm/hmm: Clean up some coding style and comments

From: Ralph Campbell <rcampbell@nvidia.com>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>,
	John Hubbard <jhubbard@nvidia.com>,
	Ira Weiny <ira.weiny@intel.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Arnd Bergmann <arnd@arndb.de>,
	Balbir Singh <bsingharora@gmail.com>,
	Dan Carpenter <dan.carpenter@oracle.com>,
	"Matthew Wilcox" <willy@infradead.org>,
	Souptick Joarder <jrdr.linux@gmail.com>,
	"Andrew Morton" <akpm@linux-foundation.org>
Subject: Re: [PATCH 2/5] mm/hmm: Clean up some coding style and comments
Date: Thu, 6 Jun 2019 17:44:15 -0700	[thread overview]
Message-ID: <3a91e9a7-e533-863b-ee5f-c34f1e10433c@nvidia.com> (raw)
In-Reply-To: <20190606155719.GA8896@ziepe.ca>

On 6/6/19 8:57 AM, Jason Gunthorpe wrote:
> On Mon, May 06, 2019 at 04:29:39PM -0700, rcampbell@nvidia.com wrote:
>> @@ -924,6 +922,7 @@ int hmm_range_register(struct hmm_range *range,
>>   		       unsigned page_shift)
>>   {
>>   	unsigned long mask = ((1UL << page_shift) - 1UL);
>> +	struct hmm *hmm;
>>   
>>   	range->valid = false;
>>   	range->hmm = NULL;
> 
> I was finishing these patches off and noticed that 'hmm' above is
> never initialized.
> 
> I added the below to this patch:
> 
> diff --git a/mm/hmm.c b/mm/hmm.c
> index 678873eb21930a..8e7403f081f44a 100644
> --- a/mm/hmm.c
> +++ b/mm/hmm.c
> @@ -932,19 +932,20 @@ int hmm_range_register(struct hmm_range *range,
>   	range->start = start;
>   	range->end = end;
>   
> -	range->hmm = hmm_get_or_create(mm);
> -	if (!range->hmm)
> +	hmm = hmm_get_or_create(mm);
> +	if (!hmm)
>   		return -EFAULT;
>   
>   	/* Check if hmm_mm_destroy() was call. */
> -	if (range->hmm->mm == NULL || range->hmm->dead) {
> -		hmm_put(range->hmm);
> +	if (hmm->mm == NULL || hmm->dead) {
> +		hmm_put(hmm);
>   		return -EFAULT;
>   	}
>   
>   	/* Initialize range to track CPU page table updates. */
> -	mutex_lock(&range->hmm->lock);
> +	mutex_lock(&hmm->lock);
>   
> +	range->hmm = hmm;
>   	list_add_rcu(&range->list, &hmm->ranges);
>   
>   	/*
> 
> Which I think was the intent of adding the 'struct hmm *'. I prefer
> this arrangement as it does not set an leave an invalid hmm pointer in
> the range if there is a failure..
> 
> Most probably the later patches fixed this up?
> 
> Please confirm, thanks
> 
> Regards,
> Jason
> 

Yes, you understand correctly. That was the intended clean up.
I must have split my original patch set incorrectly.