On Wed 22-02-17 14:39:24, Minchan Kim wrote:
> With rw_page, page_endio is used for completing IO on a page
> and it propagates write error to the address space if the IO
> fails. The problem is it accesses page->mapping directly which
> might be okay for file-backed pages but it shouldn't for
> anonymous page. Otherwise, it can corrupt one of field from
> anon_vma under us and system goes panic randomly.
I was about to say that anonymous pages shouldn't hit that path because
the end_swap_bio_write doesn call page_endio. But then I've noticed that
zram does call this function. On a closer look, though, it doesn't seem
to call it with err != 0 so it cannot hit this path. So I am wondering
whether this actually fixes anything. Why it has been marked for stable?
>
> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
> ---
> mm/filemap.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 2ba46f410c7c..1944c631e3e6 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -1008,9 +1008,12 @@ void page_endio(struct page *page, bool is_write, int err)
> unlock_page(page);
> } else {
> if (err) {
> + struct address_space *mapping;
> +
> SetPageError(page);
> - if (page->mapping)
> - mapping_set_error(page->mapping, err);
> + mapping = page_mapping(page);
> + if (mapping)
> + mapping_set_error(mapping, err);
> }
> end_page_writeback(page);
> }
> --
> 2.7.4
--
Michal Hocko
SUSE Labs