[PATCH 5.4 102/214] block: Fix page_is_mergeable() for compound pages

Greg Kroah-Hartman
2020-09-01T16:23:47Z

From: Matthew Wilcox (Oracle) <willy@infradead.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@infradead.org>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.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