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

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Date:   Thu, 6 Jun 2019 12:57:19 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     rcampbell@...dia.com
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        John Hubbard <jhubbard@...dia.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Arnd Bergmann <arnd@...db.de>,
        Balbir Singh <bsingharora@...il.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Souptick Joarder <jrdr.linux@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2/5] mm/hmm: Clean up some coding style and comments

On Mon, May 06, 2019 at 04:29:39PM -0700, rcampbell@...dia.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