On Tue, Jun 11, 2019 at 05:10:06PM +0200, Christoph Hellwig wrote: > 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@xxxxxxxxxxxxxxxxxxxxx> > Signed-off-by: Christoph Hellwig <hch@xxxxxx> > --- > block/bio.c | 12 ++++++++++-- > 1 file changed, 10 insertions(+), 2 deletions(-) > > diff --git a/block/bio.c b/block/bio.c > index c34327aa9216..0d841ba4373a 100644 > --- a/block/bio.c > +++ b/block/bio.c > @@ -891,6 +891,7 @@ 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; > @@ -911,8 +912,15 @@ 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; > } Looks fine for v5.2: Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx> Thanks, Ming
