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From:   Matthew Wilcox <willy@infradead.org>
To:     linux-fsdevel@vger.kernel.org
Cc:     "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: [PATCH v6 21/51] block: Support THPs in page_is_mergeable
Date:   Wed, 10 Jun 2020 13:13:15 -0700
Message-Id: <20200610201345.13273-22-willy@infradead.org>
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From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

page_is_mergeable() would incorrectly claim that two IOs were on different
pages because they were on different base pages rather than on the
same THP.  This led to a reference counting bug in iomap.  Simplify the
'same_page' test by just comparing whether we have the same struct page
instead of doing arithmetic on the physical addresses.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 block/bio.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/bio.c b/block/bio.c
index 5235da6434aa..cd677cde853d 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -747,7 +747,7 @@ static inline bool page_is_mergeable(const struct bio_vec *bv,
 	if (xen_domain() && !xen_biovec_phys_mergeable(bv, page))
 		return false;
 
-	*same_page = ((vec_end_addr & PAGE_MASK) == page_addr);
+	*same_page = bv->bv_page == page;
 	if (!*same_page && pfn_to_page(PFN_DOWN(vec_end_addr)) + 1 != page)
 		return false;
 	return true;
-- 
2.26.2