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Date: Wed, 25 Aug 2021 20:15:42 +0100
From: Matthew Wilcox <willy@infradead.org>
To: Joao Martins <joao.m.martins@oracle.com>
Cc: Dan Williams <dan.j.williams@intel.com>, Linux MM <linux-mm@kvack.org>,
	Vishal Verma <vishal.l.verma@intel.com>,
	Dave Jiang <dave.jiang@intel.com>,
	Naoya Horiguchi <naoya.horiguchi@nec.com>,
	Jason Gunthorpe <jgg@ziepe.ca>, John Hubbard <jhubbard@nvidia.com>,
	Jane Chu <jane.chu@oracle.com>,
	Muchun Song <songmuchun@bytedance.com>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Jonathan Corbet <corbet@lwn.net>,
	Linux NVDIMM <nvdimm@lists.linux.dev>,
	Linux Doc Mailing List <linux-doc@vger.kernel.org>
Subject: Re: [PATCH v3 13/14] mm/gup: grab head page refcount once for group
 of subpages
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 <20210714193542.21857-14-joao.m.martins@oracle.com>
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In-Reply-To: <21939df3-9376-25f2-bf94-acb55ef49307@oracle.com>

On Wed, Aug 25, 2021 at 08:10:39PM +0100, Joao Martins wrote:
> @@ -2273,8 +2273,7 @@ static int __gup_device_huge(unsigned long pfn, unsigned long addr,
>                 refs = record_subpages(page, addr, next, pages + *nr);
> 
>                 SetPageReferenced(head);
> -               pinned_head = try_grab_compound_head(head, refs, flags);
> -               if (unlikely(!pinned_head)) {
> +               if (unlikely(!try_grab_compound_head(head, refs, flags))) {
>                         if (PageCompound(head))

BTW, you can just check PageHead(head).  We know it can't be PageTail ...