block: bio_iov_iter_get_pages: fix size of last iovec

commit b403ea2404889e1227812fa9657667a1deb9c694 upstream.

If the last page of the bio is not "full", the length of the last
vector slot needs to be corrected. This slot has the index
(bio->bi_vcnt - 1), but only in bio->bi_io_vec. In the "bv" helper
array, which is shifted by the value of bio->bi_vcnt at function
invocation, the correct index is (nr_pages - 1).

v2: improved readability following suggestions from Ming Lei.
v3: followed a formatting suggestion from Christoph Hellwig.

Fixes: 2cefe4dbaadf ("block: add bio_iov_iter_get_pages()")
Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin Wilck <mwilck@suse.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/block/bio.c b/block/bio.c
index 90f19d7df66cf73ce80e8eade310105bfa17ba3d..e5df69918d1a7418d88e1191831e56b106ecc246 100644 (file)
--- a/block/bio.c
+++ b/block/bio.c
@@ -881,16 +881,16 @@ EXPORT_SYMBOL(bio_add_page);
  */
 int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
 {
-       unsigned short nr_pages = bio->bi_max_vecs - bio->bi_vcnt;
+       unsigned short nr_pages = bio->bi_max_vecs - bio->bi_vcnt, idx;
        struct bio_vec *bv = bio->bi_io_vec + bio->bi_vcnt;
        struct page **pages = (struct page **)bv;
-       size_t offset, diff;
+       size_t offset;
        ssize_t size;
 
        size = iov_iter_get_pages(iter, pages, LONG_MAX, nr_pages, &offset);
        if (unlikely(size <= 0))
                return size ? size : -EFAULT;
-       nr_pages = (size + offset + PAGE_SIZE - 1) / PAGE_SIZE;
+       idx = nr_pages = (size + offset + PAGE_SIZE - 1) / PAGE_SIZE;
 
        /*
         * Deep magic below:  We need to walk the pinned pages backwards
@@ -903,17 +903,15 @@ int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
        bio->bi_iter.bi_size += size;
        bio->bi_vcnt += nr_pages;
 
-       diff = (nr_pages * PAGE_SIZE - offset) - size;
-       while (nr_pages--) {
-               bv[nr_pages].bv_page = pages[nr_pages];
-               bv[nr_pages].bv_len = PAGE_SIZE;
-               bv[nr_pages].bv_offset = 0;
+       while (idx--) {
+               bv[idx].bv_page = pages[idx];
+               bv[idx].bv_len = PAGE_SIZE;
+               bv[idx].bv_offset = 0;
        }
 
        bv[0].bv_offset += offset;
        bv[0].bv_len -= offset;
-       if (diff)
-               bv[bio->bi_vcnt - 1].bv_len -= diff;
+       bv[nr_pages - 1].bv_len -= nr_pages * PAGE_SIZE - offset - size;
 
        iov_iter_advance(iter, size);
        return 0;