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    Subject[PATCH 3/6] block, fs: assert that key paths use iovecs, and nothing else
    Date
    From: John Hubbard <jhubbard@nvidia.com>

    Upcoming changes to Direct IO will change it from acquiring pages via
    get_user_pages_fast(), to calling pin_user_pages_fast() instead.

    Place a few assertions at key points, that the pages are IOVEC (user
    pages), to enforce the assumptions that there are no kernel or pipe or
    other odd variations being passed.

    Signed-off-by: John Hubbard <jhubbard@nvidia.com>
    ---
    block/bio.c | 4 ++++
    fs/direct-io.c | 2 ++
    2 files changed, 6 insertions(+)

    diff --git a/block/bio.c b/block/bio.c
    index b15f5466ce08..4679d6539e2d 100644
    --- a/block/bio.c
    +++ b/block/bio.c
    @@ -1167,6 +1167,8 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
    BUILD_BUG_ON(PAGE_PTRS_PER_BVEC < 2);
    pages += entries_left * (PAGE_PTRS_PER_BVEC - 1);

    + WARN_ON_ONCE(!iter_is_iovec(iter));
    +
    size = iov_iter_get_pages(iter, pages, LONG_MAX, nr_pages, &offset);
    if (unlikely(size <= 0))
    return size ? size : -EFAULT;
    @@ -1217,6 +1219,8 @@ static int __bio_iov_append_get_pages(struct bio *bio, struct iov_iter *iter)
    BUILD_BUG_ON(PAGE_PTRS_PER_BVEC < 2);
    pages += entries_left * (PAGE_PTRS_PER_BVEC - 1);

    + WARN_ON_ONCE(!iter_is_iovec(iter));
    +
    size = iov_iter_get_pages(iter, pages, LONG_MAX, nr_pages, &offset);
    if (unlikely(size <= 0))
    return size ? size : -EFAULT;
    diff --git a/fs/direct-io.c b/fs/direct-io.c
    index 38bca4980a1c..7dbbbfef300d 100644
    --- a/fs/direct-io.c
    +++ b/fs/direct-io.c
    @@ -169,6 +169,8 @@ static inline int dio_refill_pages(struct dio *dio, struct dio_submit *sdio)
    {
    ssize_t ret;

    + WARN_ON_ONCE(!iter_is_iovec(sdio->iter));
    +
    ret = iov_iter_get_pages(sdio->iter, dio->pages, LONG_MAX, DIO_PAGES,
    &sdio->from);

    --
    2.35.1
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