patches/kernel/0010-block-bio_iov_iter_get_pages-fix-size-of-last-iovec.patch

   1 From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
   2 From: Martin Wilck <mwilck@suse.com>
   3 Date: Tue, 9 Oct 2018 17:04:40 +0100
   4 Subject: [PATCH] block: bio_iov_iter_get_pages: fix size of last iovec
   5
   6 Buglink: https://bugs.launchpad.net/bugs/1796542
   7
   8 If the last page of the bio is not "full", the length of the last
   9 vector slot needs to be corrected. This slot has the index
  10 (bio->bi_vcnt - 1), but only in bio->bi_io_vec. In the "bv" helper
  11 array, which is shifted by the value of bio->bi_vcnt at function
  12 invocation, the correct index is (nr_pages - 1).
  13
  14 v2: improved readability following suggestions from Ming Lei.
  15 v3: followed a formatting suggestion from Christoph Hellwig.
  16
  17 Fixes: 2cefe4dbaadf ("block: add bio_iov_iter_get_pages()")
  18 Reviewed-by: Hannes Reinecke <hare@suse.com>
  19 Reviewed-by: Ming Lei <ming.lei@redhat.com>
  20 Reviewed-by: Jan Kara <jack@suse.cz>
  21 Reviewed-by: Christoph Hellwig <hch@lst.de>
  22 Signed-off-by: Martin Wilck <mwilck@suse.com>
  23 Signed-off-by: Jens Axboe <axboe@kernel.dk>
  24 (cherry picked from commit b403ea2404889e1227812fa9657667a1deb9c694)
  25 Signed-off-by: Colin Ian King <colin.king@canonical.com>
  26 Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
  27 ---
  28  block/bio.c | 18 ++++++++----------
  29  1 file changed, 8 insertions(+), 10 deletions(-)
  30
  31 diff --git a/block/bio.c b/block/bio.c
  32 index 2636d15af979..d76372a6a5fe 100644
  33 --- a/block/bio.c
  34 +++ b/block/bio.c
  35 @@ -911,16 +911,16 @@ EXPORT_SYMBOL(bio_add_page);
  36   */
  37  int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
  38  {
  39 -       unsigned short nr_pages = bio->bi_max_vecs - bio->bi_vcnt;
  40 +       unsigned short nr_pages = bio->bi_max_vecs - bio->bi_vcnt, idx;
  41         struct bio_vec *bv = bio->bi_io_vec + bio->bi_vcnt;
  42         struct page **pages = (struct page **)bv;
  43 -       size_t offset, diff;
  44 +       size_t offset;
  45         ssize_t size;
  46
  47         size = iov_iter_get_pages(iter, pages, LONG_MAX, nr_pages, &offset);
  48         if (unlikely(size <= 0))
  49                 return size ? size : -EFAULT;
  50 -       nr_pages = (size + offset + PAGE_SIZE - 1) / PAGE_SIZE;
  51 +       idx = nr_pages = (size + offset + PAGE_SIZE - 1) / PAGE_SIZE;
  52
  53         /*
  54          * Deep magic below:  We need to walk the pinned pages backwards
  55 @@ -933,17 +933,15 @@ int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
  56         bio->bi_iter.bi_size += size;
  57         bio->bi_vcnt += nr_pages;
  58
  59 -       diff = (nr_pages * PAGE_SIZE - offset) - size;
  60 -       while (nr_pages--) {
  61 -               bv[nr_pages].bv_page = pages[nr_pages];
  62 -               bv[nr_pages].bv_len = PAGE_SIZE;
  63 -               bv[nr_pages].bv_offset = 0;
  64 +       while (idx--) {
  65 +               bv[idx].bv_page = pages[idx];
  66 +               bv[idx].bv_len = PAGE_SIZE;
  67 +               bv[idx].bv_offset = 0;
  68         }
  69
  70         bv[0].bv_offset += offset;
  71         bv[0].bv_len -= offset;
  72 -       if (diff)
  73 -               bv[bio->bi_vcnt - 1].bv_len -= diff;
  74 +       bv[nr_pages - 1].bv_len -= nr_pages * PAGE_SIZE - offset - size;
  75
  76         iov_iter_advance(iter, size);
  77         return 0;