linux-kernel - [PATCH v2 10/28] gup: Turn hpage_pincount_sub() into page_pincount

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Message-Id: <20220110042406.499429-11-willy@infradead.org>
Date:   Mon, 10 Jan 2022 04:23:48 +0000
From:   "Matthew Wilcox (Oracle)" <willy@...radead.org>
To:     linux-mm@...ck.org
Cc:     "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        John Hubbard <jhubbard@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        William Kucharski <william.kucharski@...cle.com>,
        linux-kernel@...r.kernel.org, Jason Gunthorpe <jgg@...pe.ca>
Subject: [PATCH v2 10/28] gup: Turn hpage_pincount_sub() into page_pincount_sub()

Remove an unnecessary VM_BUG_ON by handling pages both with and without
a pincount field in page_pincount_sub().

Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
---
 mm/gup.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 3ed9907f3c8d..aed48de3912e 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -48,12 +48,15 @@ static void page_pincount_add(struct page *page, int refs)
 		page_ref_add(page, refs * (GUP_PIN_COUNTING_BIAS - 1));
 }
 
-static void hpage_pincount_sub(struct page *page, int refs)
+static int page_pincount_sub(struct page *page, int refs)
 {
-	VM_BUG_ON_PAGE(!hpage_pincount_available(page), page);
 	VM_BUG_ON_PAGE(page != compound_head(page), page);
 
-	atomic_sub(refs, compound_pincount_ptr(page));
+	if (hpage_pincount_available(page))
+		atomic_sub(refs, compound_pincount_ptr(page));
+	else
+		refs *= GUP_PIN_COUNTING_BIAS;
+	return refs;
 }
 
 /* Equivalent to calling put_page() @refs times. */
@@ -177,11 +180,7 @@ static void put_compound_head(struct page *page, int refs, unsigned int flags)
 	if (flags & FOLL_PIN) {
 		mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_RELEASED,
 				    refs);
-
-		if (hpage_pincount_available(page))
-			hpage_pincount_sub(page, refs);
-		else
-			refs *= GUP_PIN_COUNTING_BIAS;
+		refs = page_pincount_sub(page, refs);
 	}
 
 	put_page_refs(page, refs);
-- 
2.33.0