On Mon 20-06-22 19:05:36, Alistair Popple wrote:
> Commit 793917d997df ("mm/readahead: Add large folio readahead")
> introduced support for using large folios for filebacked pages if the
> filesystem supports it.
>
> page_cache_ra_order() was introduced to allocate and add these large
> folios to the page cache. However adding pages to the page cache should
> be serialized against truncation and hole punching by taking
> invalidate_lock. Not doing so can lead to data races resulting in stale
> data getting added to the page cache and marked up-to-date. See commit
> 730633f0b7f9 ("mm: Protect operations adding pages to page cache with
> invalidate_lock") for more details.
>
> This issue was found by inspection but a testcase revealed it was
> possible to observe in practice on XFS. Fix this by taking
> invalidate_lock in page_cache_ra_order(), to mirror what is done for the
> non-thp case in page_cache_ra_unbounded().
>
> Signed-off-by: Alistair Popple <apopple@xxxxxxxxxx>
> Fixes: 793917d997df ("mm/readahead: Add large folio readahead")
Thanks for catching this! Your fix looks good to me so feel free to add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Honza
> ---
> mm/readahead.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/mm/readahead.c b/mm/readahead.c
> index 4a60cdb64262..38635af5bab7 100644
> --- a/mm/readahead.c
> +++ b/mm/readahead.c
> @@ -508,6 +508,7 @@ void page_cache_ra_order(struct readahead_control *ractl,
> new_order--;
> }
>
> + filemap_invalidate_lock_shared(mapping);
> while (index <= limit) {
> unsigned int order = new_order;
>
> @@ -534,6 +535,7 @@ void page_cache_ra_order(struct readahead_control *ractl,
> }
>
> read_pages(ractl);
> + filemap_invalidate_unlock_shared(mapping);
>
> /*
> * If there were already pages in the page cache, then we may have
> --
> 2.35.1
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
