Looks good.
Reviewed-by: William Kucharski <william.kucharski@xxxxxxxxxx>
> On Aug 2, 2022, at 21:18, Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
>
> On Tue, Aug 02, 2022 at 05:46:37PM -0700, Andrew Morton wrote:
>>> On Sat, 30 Jul 2022 05:25:18 +0100 "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx> wrote:
>>>
>>> If we allocate a new page, we need to make sure that our folio matches
>>> that new page. This will be solved by changing shmem_replace_page()
>>> to shmem_replace_folio(), but this is the minimal fix.
>>>
>>> ...
>>>
>>> --- a/mm/shmem.c
>>> +++ b/mm/shmem.c
>>> @@ -1771,6 +1771,7 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
>>>
>>> if (shmem_should_replace_folio(folio, gfp)) {
>>> error = shmem_replace_page(&page, gfp, info, index);
>>> + folio = page_folio(page);
>>> if (error)
>>> goto failed;
>>> }
>>
>> What are the user-visible runtime effects of the bug?
>>
>> Should we backport this into 5.19.X?
>
> Definitely should be backported. The next line not visible in this
> patch context says:
>
> error = shmem_add_to_page_cache(folio, mapping, index,
> swp_to_radix_entry(swap), gfp,
> charge_mm);
>
> so if we do end up in this path, we store the wrong page in the
> shmem inode's page cache, and I would rather imagine that data
> corruption ensues.
>
