linux-kernel - [PATCH 5.4 102/214] block: Fix page_is

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Date:   Tue,  1 Sep 2020 17:09:42 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Ming Lei <ming.lei@...hat.com>, Jens Axboe <axboe@...nel.dk>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.4 102/214] block: Fix page_is_mergeable() for compound pages

From: Matthew Wilcox (Oracle) <willy@...radead.org>

[ Upstream commit d81665198b83e55a28339d1f3e4890ed8a434556 ]

If we pass in an offset which is larger than PAGE_SIZE, then
page_is_mergeable() thinks it's not mergeable with the previous bio_vec,
leading to a large number of bio_vecs being used.  Use a slightly more
obvious test that the two pages are compatible with each other.

Fixes: 52d52d1c98a9 ("block: only allow contiguous page structs in a bio_vec")
Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
Reviewed-by: Ming Lei <ming.lei@...hat.com>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 block/bio.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index 94d697217887a..87505a93bcff6 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -683,8 +683,8 @@ static inline bool page_is_mergeable(const struct bio_vec *bv,
 		struct page *page, unsigned int len, unsigned int off,
 		bool *same_page)
 {
-	phys_addr_t vec_end_addr = page_to_phys(bv->bv_page) +
-		bv->bv_offset + bv->bv_len - 1;
+	size_t bv_end = bv->bv_offset + bv->bv_len;
+	phys_addr_t vec_end_addr = page_to_phys(bv->bv_page) + bv_end - 1;
 	phys_addr_t page_addr = page_to_phys(page);
 
 	if (vec_end_addr + 1 != page_addr + off)
@@ -693,9 +693,9 @@ static inline bool page_is_mergeable(const struct bio_vec *bv,
 		return false;
 
 	*same_page = ((vec_end_addr & PAGE_MASK) == page_addr);
-	if (!*same_page && pfn_to_page(PFN_DOWN(vec_end_addr)) + 1 != page)
-		return false;
-	return true;
+	if (*same_page)
+		return true;
+	return (bv->bv_page + bv_end / PAGE_SIZE) == (page + off / PAGE_SIZE);
 }
 
 static bool bio_try_merge_pc_page(struct request_queue *q, struct bio *bio,
-- 
2.25.1