[PATCH] iov_iter: Four fixes for ITER_XARRAY

[David Wysochanski]

On Sun, Apr 25, 2021 at 7:15 PM David Howells <dhowells at redhat.com> wrote:
>
> Hi Al,
>
> I think this patch should include all the fixes necessary.  I could merge
> it in, but I think it might be better to tag it on the end as an additional
> patch.
>
> David
> ---
> iov_iter: Four fixes for ITER_XARRAY
>
> Fix four things[1] in the patch that adds ITER_XARRAY[2]:
>
>  (1) Remove the address_space struct predeclaration.  This is a holdover
>      from when it was ITER_MAPPING.
>
>  (2) Fix _copy_mc_to_iter() so that the xarray segment updates count and
>      iov_offset in the iterator before returning.
>
>  (3) Fix iov_iter_alignment() to not loop in the xarray case.  Because the
>      middle pages are all whole pages, only the end pages need be
>      considered - and this can be reduced to just looking at the start
>      position in the xarray and the iteration size.
>
>  (4) Fix iov_iter_advance() to limit the size of the advance to no more
>      than the remaining iteration size.
>
> Reported-by: Al Viro <viro at zeniv.linux.org.uk>
> Signed-off-by: David Howells <dhowells at redhat.com>
> Link: https://lore.kernel.org/r/YIVrJT8GwLI0Wlgx@zeniv-ca.linux.org.uk [1]
> Link: https://lore.kernel.org/r/161918448151.3145707.11541538916600921083.stgit@warthog.procyon.org.uk [2]
> ---
>  include/linux/uio.h |    1 -
>  lib/iov_iter.c      |    5 +++++
>  2 files changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/uio.h b/include/linux/uio.h
> index 5f5ffc45d4aa..d3ec87706d75 100644
> --- a/include/linux/uio.h
> +++ b/include/linux/uio.h
> @@ -10,7 +10,6 @@
>  #include <uapi/linux/uio.h>
>
>  struct page;
> -struct address_space;
>  struct pipe_inode_info;
>
>  struct kvec {
> diff --git a/lib/iov_iter.c b/lib/iov_iter.c
> index 44fa726a8323..61228a6c69f8 100644
> --- a/lib/iov_iter.c
> +++ b/lib/iov_iter.c
> @@ -791,6 +791,8 @@ size_t _copy_mc_to_iter(const void *addr, size_t bytes, struct iov_iter *i)
>                         curr_addr = (unsigned long) from;
>                         bytes = curr_addr - s_addr - rem;
>                         rcu_read_unlock();
> +                       i->iov_offset += bytes;
> +                       i->count -= bytes;
>                         return bytes;
>                 }
>                 })
> @@ -1147,6 +1149,7 @@ void iov_iter_advance(struct iov_iter *i, size_t size)
>                 return;
>         }
>         if (unlikely(iov_iter_is_xarray(i))) {
> +               size = min(size, i->count);
>                 i->iov_offset += size;
>                 i->count -= size;
>                 return;
> @@ -1346,6 +1349,8 @@ unsigned long iov_iter_alignment(const struct iov_iter *i)
>                         return size | i->iov_offset;
>                 return size;
>         }
> +       if (unlikely(iov_iter_is_xarray(i)))
> +               return (i->xarray_start + i->iov_offset) | i->count;
>         iterate_all_kinds(i, size, v,
>                 (res |= (unsigned long)v.iov_base | v.iov_len, 0),
>                 res |= v.bv_offset | v.bv_len,
>

You can add
Tested-by: Dave Wysochanski <dwysocha at redhat.com>

I added this patch on top of your v7 series then added my current
NFS patches to use netfs lib.
I ran xfstests with fscache enabled on NFS versions (3, 4.0, 4.1, 4.2),
as well as connectathon and some unit tests.