[Devel] [PATCH RH9 v2] fuse/kio: do not use sendpage on pages which cannot be sendpaged

[Alexey Kuznetsov]

Ack

On Wed, Apr 19, 2023 at 7:17 PM Kui Liu <Kui.Liu at acronis.com> wrote:
>
> It looks like the new API iov_iter_get_pages is not safe for use
> when trying to get a page from a bvec to be sent by kernel_sendpage().
> So just revert back our own implentation where we check the page
> before making get_page(), if the page can't be sendpage, fall back
> to copy mode.
>
> Affects: #PSBM-146821, #PSBM-146846
> https://jira.vzint.dev/browse/PSBM-146821
> https://jira.vzint.dev/browse/PSBM-146846
> Signed-off-by: Liu Kui <Kui.Liu at acronis.com>
> ---
>  fs/fuse/kio/pcs/pcs_sock_io.c | 26 ++++++++++++++++++++------
>  1 file changed, 20 insertions(+), 6 deletions(-)
>
> diff --git a/fs/fuse/kio/pcs/pcs_sock_io.c b/fs/fuse/kio/pcs/pcs_sock_io.c
> index 552b82ab398b..710940eafa34 100644
> --- a/fs/fuse/kio/pcs/pcs_sock_io.c
> +++ b/fs/fuse/kio/pcs/pcs_sock_io.c
> @@ -143,16 +143,30 @@ static int do_send_one_seg(struct socket *sock, struct iov_iter *it, size_t left
>         }
>
>         if (iov_iter_is_bvec(it)) {
> -               /* Zerocopy */
>                 size_t offset;
>                 ssize_t len;
>                 struct page *page;
>
> -               len = iov_iter_get_pages(it, &page, size, 1, &offset);
> -               BUG_ON(len <= 0);
> -
> -               ret = kernel_sendpage(sock, page, offset, len, flags);
> -               put_page(page);
> +               /* Only support single page bvec here */
> +               page = it->bvec->bv_page;
> +               offset = it->bvec->bv_offset + it->iov_offset;
> +               len = min(size, it->bvec->bv_len - it->iov_offset);
> +
> +               if (sendpage_ok(page)) {
> +                       /* Zero copy */
> +                       get_page(page);
> +                       ret = kernel_sendpage(sock, page, offset, len, flags);
> +                       put_page(page);
> +               } else {
> +                       /* Fall back to copy mode */
> +                       struct msghdr msg = { .msg_flags = flags };
> +                       struct kvec kv;
> +
> +                       kv.iov_base = kmap(page) + offset;
> +                       kv.iov_len = len;
> +                       ret = kernel_sendmsg(sock, &msg, &kv, 1, size);
> +                       kunmap(page);
> +               }
>         }
>
>  out:
> --
> 2.32.0 (Apple Git-132)
>
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