On Thu, Jun 6, 2019 at 2:10 AM Jan Kara <jack@xxxxxxx> wrote:
>
> When inserting entry into xarray, we store mapping and index in
> corresponding struct pages for memory error handling. When it happened
> that one process was mapping file at PMD granularity while another
> process at PTE granularity, we could wrongly deassociate PMD range and
> then reassociate PTE range leaving the rest of struct pages in PMD range
> without mapping information which could later cause missed notifications
> about memory errors. Fix the problem by calling the association /
> deassociation code if and only if we are really going to update the
> xarray (deassociating and associating zero or empty entries is just
> no-op so there's no reason to complicate the code with trying to avoid
> the calls for these cases).
Looks good to me, I assume this also needs:
Cc: <stable@xxxxxxxxxxxxxxx>
Fixes: d2c997c0f145 ("fs, dax: use page->mapping to warn if truncate
collides with a busy page")
>
> Signed-off-by: Jan Kara <jack@xxxxxxx>
> ---
> fs/dax.c | 9 ++++-----
> 1 file changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index f74386293632..9fd908f3df32 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -728,12 +728,11 @@ static void *dax_insert_entry(struct xa_state *xas,
>
> xas_reset(xas);
> xas_lock_irq(xas);
> - if (dax_entry_size(entry) != dax_entry_size(new_entry)) {
> + if (dax_is_zero_entry(entry) || dax_is_empty_entry(entry)) {
> + void *old;
> +
> dax_disassociate_entry(entry, mapping, false);
> dax_associate_entry(new_entry, mapping, vmf->vma, vmf->address);
> - }
> -
> - if (dax_is_zero_entry(entry) || dax_is_empty_entry(entry)) {
> /*
> * Only swap our new entry into the page cache if the current
> * entry is a zero page or an empty entry. If a normal PTE or
> @@ -742,7 +741,7 @@ static void *dax_insert_entry(struct xa_state *xas,
> * existing entry is a PMD, we will just leave the PMD in the
> * tree and dirty it if necessary.
> */
> - void *old = dax_lock_entry(xas, new_entry);
> + old = dax_lock_entry(xas, new_entry);
> WARN_ON_ONCE(old != xa_mk_value(xa_to_value(entry) |
> DAX_LOCKED));
> entry = new_entry;
> --
> 2.16.4
>
