On Fri, 2021-06-11 at 11:55 -0400, Jeff Layton wrote:
> It's not sufficient to skip reading when the pos is beyond the EOF.
> There may be data at the head of the page that we need to fill in
> before the write. Only elide the read if the pos is beyond the last page
> in the file.
>
> Reported-by: Andrew W Elble <aweits@xxxxxxx>
> Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> ---
> fs/ceph/addr.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> I've not tested this at all yet, but I think this is probably what we'll
> want for stable series v5.10.z - v5.12.z.
>
> diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
> index 35c83f65475b..9f60f541b423 100644
> --- a/fs/ceph/addr.c
> +++ b/fs/ceph/addr.c
> @@ -1353,11 +1353,11 @@ static int ceph_write_begin(struct file *file, struct address_space *mapping,
> /*
> * In some cases we don't need to read at all:
> * - full page write
> - * - write that lies completely beyond EOF
> + * - write that lies in a page that is completely beyond EOF
> * - write that covers the the page from start to EOF or beyond it
> */
> if ((pos_in_page == 0 && len == PAGE_SIZE) ||
> - (pos >= i_size_read(inode)) ||
> + (index >= (i_size_read(inode) << PAGE_SHIFT)) ||
...and this should be:
(index > (i_size_read(inode) << PAGE_SHIFT)) ||
We only get to skip the read if the write pos is _beyond_ the last page.
> (pos_in_page == 0 && (pos + len) >= i_size_read(inode))) {
> zero_user_segments(page, 0, pos_in_page,
> pos_in_page + len, PAGE_SIZE);
--
Jeff Layton <jlayton@xxxxxxxxxx>
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