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From:   "Matthew Wilcox (Oracle)" <willy@infradead.org>
To:     linux-mm@kvack.org
Cc:     "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        linux-kernel@vger.kernel.org
Subject: [PATCH 01/75] mm/gup: Increment the page refcount before the pincount
Date:   Fri,  4 Feb 2022 19:57:38 +0000
Message-Id: <20220204195852.1751729-2-willy@infradead.org>
In-Reply-To: <20220204195852.1751729-1-willy@infradead.org>
References: <20220204195852.1751729-1-willy@infradead.org>
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We should always increase the refcount before doing anything else to
the page so that other page users see the elevated refcount first.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 mm/gup.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index a9d4d724aef7..08020987dfc0 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -220,18 +220,18 @@ bool __must_check try_grab_page(struct page *page, unsigned int flags)
 		if (WARN_ON_ONCE(page_ref_count(page) <= 0))
 			return false;
 
-		if (hpage_pincount_available(page))
-			hpage_pincount_add(page, 1);
-		else
-			refs = GUP_PIN_COUNTING_BIAS;
-
 		/*
 		 * Similar to try_grab_compound_head(): even if using the
 		 * hpage_pincount_add/_sub() routines, be sure to
 		 * *also* increment the normal page refcount field at least
 		 * once, so that the page really is pinned.
 		 */
-		page_ref_add(page, refs);
+		if (hpage_pincount_available(page)) {
+			page_ref_add(page, 1);
+			hpage_pincount_add(page, 1);
+		} else {
+			page_ref_add(page, GUP_PIN_COUNTING_BIAS);
+		}
 
 		mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_ACQUIRED, 1);
 	}
-- 
2.34.1