On Wed, May 25, 2022 at 02:40:40PM +0800, Miaohe Lin wrote:
> On 2022/5/25 12:32, HORIGUCHI NAOYA(堀口 直也) wrote:
> > On Thu, May 19, 2022 at 08:50:29PM +0800, Miaohe Lin wrote:
> >> When swap in shmem error at swapoff time, there would be a infinite loop
> >> in the while loop in shmem_unuse_inode(). It's because swapin error is
> >> deliberately ignored now and thus info->swapped will never reach 0. So
> >> we can't escape the loop in shmem_unuse().
> >>
> >> In order to fix the issue, swapin_error entry is stored in the mapping
> >> when swapin error occurs. So the swapcache page can be freed and the
> >> user won't end up with a permanently mounted swap because a sector is
> >> bad. If the page is accessed later, the user process will be killed
> >> so that corrupted data is never consumed. On the other hand, if the
> >> page is never accessed, the user won't even notice it.
> >>
> >> Reported-by: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
> >> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
> >> ---
> >
> > ...
> >> @@ -1672,6 +1676,36 @@ static int shmem_replace_page(struct page **pagep, gfp_t gfp,
> >> return error;
> >> }
> >>
> >> +static void shmem_set_folio_swapin_error(struct inode *inode, pgoff_t index,
> >> + struct folio *folio, swp_entry_t swap)
> >> +{
> >> + struct address_space *mapping = inode->i_mapping;
> >> + struct shmem_inode_info *info = SHMEM_I(inode);
> >> + swp_entry_t swapin_error;
> >> + void *old;
> >> +
> >> + swapin_error = make_swapin_error_entry(&folio->page);
> >> + old = xa_cmpxchg_irq(&mapping->i_pages, index,
> >> + swp_to_radix_entry(swap),
> >> + swp_to_radix_entry(swapin_error), 0);
> >> + if (old != swp_to_radix_entry(swap))
> >> + return;
> >> +
> >> + folio_wait_writeback(folio);
> >> + delete_from_swap_cache(&folio->page);
> >> + spin_lock_irq(&info->lock);
> >> + /*
> >> + * Don't treat swapin error folio as alloced. Otherwise inode->i_blocks won't
> >> + * be 0 when inode is released and thus trigger WARN_ON(inode->i_blocks) in
> >> + * shmem_evict_inode.
> >> + */
> >> + info->alloced--;
> >> + info->swapped--;
> >
> > I'm not familiar with folio yet and might miss some basic thing,
> > but is it OK to decrement by one instead of folio_nr_pages()?
>
> info->swapped is also decremented by one in shmem_swapin_folio(). In fact, no huge page
> swapin is supported yet (this is also true for non-shmem case). So I think info->swapped--
> should be OK. Or am I miss something?
OK, thanks for clarification.
Reviewed-by: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
