From: Christoph Hellwig hch@lst.de
[ Upstream commit 4569180495600ac59f5cd27f67242a6cb51254f3 ]
When multiple iovecs reference the same page, each get_user_page call will add a reference to the page. But once we've created the bio that information gets lost and only a single reference will be dropped after I/O completion. Use the same_page information returned from __bio_try_merge_page to drop additional references to pages that were already present in the bio.
Based on a patch from Ming Lei.
Link: https://lkml.org/lkml/2019/4/23/64 Fixes: 576ed913 ("block: use bio_add_page in bio_iov_iter_get_pages") Reported-by: David Gibson david@gibson.dropbear.id.au Signed-off-by: Christoph Hellwig hch@lst.de 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 | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/block/bio.c b/block/bio.c index a3c80a6c1fe5..80a25c245109 100644 --- a/block/bio.c +++ b/block/bio.c @@ -884,6 +884,7 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter) unsigned short entries_left = bio->bi_max_vecs - bio->bi_vcnt; struct bio_vec *bv = bio->bi_io_vec + bio->bi_vcnt; struct page **pages = (struct page **)bv; + bool same_page = false; ssize_t size, left; unsigned len, i; size_t offset; @@ -904,8 +905,15 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter) struct page *page = pages[i];
len = min_t(size_t, PAGE_SIZE - offset, left); - if (WARN_ON_ONCE(bio_add_page(bio, page, len, offset) != len)) - return -EINVAL; + + if (__bio_try_merge_page(bio, page, len, offset, &same_page)) { + if (same_page) + put_page(page); + } else { + if (WARN_ON_ONCE(bio_full(bio))) + return -EINVAL; + __bio_add_page(bio, page, len, offset); + } offset = 0; }