On Fri, Sep 22, 2023 at 10:22 AM Domenico Cerasuolo
<cerasuolodomenico@xxxxxxxxx> wrote:
>
> While stress-testing zswap a memory corruption was happening when writing
> back pages. __frontswap_store used to check for duplicate entries before
> attempting to store a page in zswap, this was because if the store fails
> the old entry isn't removed from the tree. This change removes duplicate
> entries in zswap_store before the actual attempt.
>
> Based on commit ce9ecca0238b ("Linux 6.6-rc2")
>
> Fixes: 42c06a0e8ebe ("mm: kill frontswap")
> Signed-off-by: Domenico Cerasuolo <cerasuolodomenico@xxxxxxxxx>
Acked-by: Nhat Pham <nphamcs@xxxxxxxxx>
> ---
> mm/zswap.c | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/mm/zswap.c b/mm/zswap.c
> index 412b1409a0d7..9146f9f19061 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -1218,6 +1218,19 @@ bool zswap_store(struct folio *folio)
> if (!zswap_enabled || !tree)
> return false;
>
> + /*
> + * If this is a duplicate, it must be removed before attempting to store
> + * it, otherwise, if the store fails the old page won't be removed from
> + * the tree, and it might be written back overriding the new data.
> + */
> + spin_lock(&tree->lock);
> + dupentry = zswap_rb_search(&tree->rbroot, offset);
> + if (dupentry) {
> + zswap_duplicate_entry++;
> + zswap_invalidate_entry(tree, dupentry);
> + }
> + spin_unlock(&tree->lock);
> +
> /*
> * XXX: zswap reclaim does not work with cgroups yet. Without a
> * cgroup-aware entry LRU, we will push out entries system-wide based on
> --
> 2.34.1
>
