patches/kernel/0012-block-bio_iov_iter_get_pages-pin-more-pages-for-mult.patch

   1 From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
   2 From: Martin Wilck <mwilck@suse.com>
   3 Date: Tue, 9 Oct 2018 17:04:42 +0100
   4 Subject: [PATCH] block: bio_iov_iter_get_pages: pin more pages for
   5  multi-segment IOs
   6
   7 Buglink: https://bugs.launchpad.net/bugs/1796542
   8
   9 bio_iov_iter_get_pages() currently only adds pages for the next non-zero
  10 segment from the iov_iter to the bio. That's suboptimal for callers,
  11 which typically try to pin as many pages as fit into the bio. This patch
  12 converts the current bio_iov_iter_get_pages() into a static helper, and
  13 introduces a new helper that allocates as many pages as
  14
  15  1) fit into the bio,
  16  2) are present in the iov_iter,
  17  3) and can be pinned by MM.
  18
  19 Error is returned only if zero pages could be pinned. Because of 3), a
  20 zero return value doesn't necessarily mean all pages have been pinned.
  21 Callers that have to pin every page in the iov_iter must still call this
  22 function in a loop (this is currently the case).
  23
  24 This change matters most for __blkdev_direct_IO_simple(), which calls
  25 bio_iov_iter_get_pages() only once. If it obtains less pages than
  26 requested, it returns a "short write" or "short read", and
  27 __generic_file_write_iter() falls back to buffered writes, which may
  28 lead to data corruption.
  29
  30 Fixes: 72ecad22d9f1 ("block: support a full bio worth of IO for simplified bdev direct-io")
  31 Reviewed-by: Christoph Hellwig <hch@lst.de>
  32 Signed-off-by: Martin Wilck <mwilck@suse.com>
  33 Signed-off-by: Jens Axboe <axboe@kernel.dk>
  34 (cherry picked from commit 17d51b10d7773e4618bcac64648f30f12d4078fb)
  35 Signed-off-by: Colin Ian King <colin.king@canonical.com>
  36 Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
  37 ---
  38  block/bio.c | 35 ++++++++++++++++++++++++++++++++---
  39  1 file changed, 32 insertions(+), 3 deletions(-)
  40
  41 diff --git a/block/bio.c b/block/bio.c
  42 index d76372a6a5fe..415c65b9c590 100644
  43 --- a/block/bio.c
  44 +++ b/block/bio.c
  45 @@ -902,14 +902,16 @@ int bio_add_page(struct bio *bio, struct page *page,
  46  EXPORT_SYMBOL(bio_add_page);
  47
  48  /**
  49 - * bio_iov_iter_get_pages - pin user or kernel pages and add them to a bio
  50 + * __bio_iov_iter_get_pages - pin user or kernel pages and add them to a bio
  51   * @bio: bio to add pages to
  52   * @iter: iov iterator describing the region to be mapped
  53   *
  54 - * Pins as many pages from *iter and appends them to @bio's bvec array. The
  55 + * Pins pages from *iter and appends them to @bio's bvec array. The
  56   * pages will have to be released using put_page() when done.
  57 + * For multi-segment *iter, this function only adds pages from the
  58 + * the next non-empty segment of the iov iterator.
  59   */
  60 -int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
  61 +static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
  62  {
  63         unsigned short nr_pages = bio->bi_max_vecs - bio->bi_vcnt, idx;
  64         struct bio_vec *bv = bio->bi_io_vec + bio->bi_vcnt;
  65 @@ -946,6 +948,33 @@ int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
  66         iov_iter_advance(iter, size);
  67         return 0;
  68  }
  69 +
  70 +/**
  71 + * bio_iov_iter_get_pages - pin user or kernel pages and add them to a bio
  72 + * @bio: bio to add pages to
  73 + * @iter: iov iterator describing the region to be mapped
  74 + *
  75 + * Pins pages from *iter and appends them to @bio's bvec array. The
  76 + * pages will have to be released using put_page() when done.
  77 + * The function tries, but does not guarantee, to pin as many pages as
  78 + * fit into the bio, or are requested in *iter, whatever is smaller.
  79 + * If MM encounters an error pinning the requested pages, it stops.
  80 + * Error is returned only if 0 pages could be pinned.
  81 + */
  82 +int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
  83 +{
  84 +       unsigned short orig_vcnt = bio->bi_vcnt;
  85 +
  86 +       do {
  87 +               int ret = __bio_iov_iter_get_pages(bio, iter);
  88 +
  89 +               if (unlikely(ret))
  90 +                       return bio->bi_vcnt > orig_vcnt ? 0 : ret;
  91 +
  92 +       } while (iov_iter_count(iter) && !bio_full(bio));
  93 +
  94 +       return 0;
  95 +}
  96  EXPORT_SYMBOL_GPL(bio_iov_iter_get_pages);
  97
  98  static void submit_bio_wait_endio(struct bio *bio)