On Thu, 26 Nov 2020, Matthew Wilcox wrote:
> On Wed, Nov 25, 2020 at 04:11:57PM -0800, Hugh Dickins wrote:
> > > + index = truncate_inode_partial_page(mapping,
> > > + page, lstart, lend);
> > > + if (index > end)
> > > + end = indices[i] - 1;
> > > }
> > > - unlock_page(page);
> >
> > The fix needed is here: instead of deleting that unlock_page(page)
> > line, it needs to be } else { unlock_page(page); }
>
> It also needs a put_page(page);
Oh yes indeed, sorry for getting that wrong. I'd misread the
pagevec_reinit() at the end as the old pagevec_release(). Do you
really need to do pagevec_remove_exceptionals() there if you're not
using pagevec_release()?
>
> That's now taken care of by truncate_inode_partial_page(), so if we're
> not calling that, we need to put the page as well. ie this:
Right, but I do find it confusing that truncate_inode_partial_page()
does the unlock_page(),put_page() whereas truncate_inode_page() does
not: I think you would do better to leave them out of _partial_page(),
even if including them there saves a couple of lines somewhere else.
But right now it's the right fix that's important: ack to yours below.
I've not yet worked out the other issues I saw: will report when I have.
Rebooted this laptop, pretty sure it missed freeing a shmem swap entry,
not yet reproduced, will study the change there later, but the non-swap
hang in generic/476 (later seen also in generic/112) more important.
Hugh
>
> +++ b/mm/shmem.c
> @@ -954,6 +954,9 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
> page, lstart, lend);
> if (index > end)
> end = indices[i] - 1;
> + } else {
> + unlock_page(page);
> + put_page(page);
> }
> }
> index = indices[i - 1] + 1;
>
> > > }
> > > + index = indices[i - 1] + 1;
> > > pagevec_remove_exceptionals(&pvec);
> > > - pagevec_release(&pvec);
> > > - index++;
> > > + pagevec_reinit(&pvec);
