In zswap_writeback_entry(), after we get a folio from __read_swap_cache_async(), we grab the tree lock again to check that the swap entry was not invalidated and recycled. If it was, we delete the folio we just added to the swap cache and exit.
However, __read_swap_cache_async() returns the folio locked when it is newly allocated, which is always true for this path, and the folio is ref'd. Make sure to unlock and put the folio before returning.
This was discovered by code inspection, probably because this path handles a race condition that should not happen often, and the bug would not crash the system, it will only strand the folio indefinitely.
Link: https://lkml.kernel.org/r/20240125085127.1327013-1-yosryahmed@google.com Fixes: 04fc7816089c ("mm: fix zswap writeback race condition") Signed-off-by: Yosry Ahmed yosryahmed@google.com Reviewed-by: Chengming Zhou zhouchengming@bytedance.com Acked-by: Johannes Weiner hannes@cmpxchg.org Reviewed-by: Nhat Pham nphamcs@gmail.com Cc: Domenico Cerasuolo cerasuolodomenico@gmail.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org (cherry picked from commit e3b63e966cac0bf78aaa1efede1827a252815a1d) Signed-off-by: Yosry Ahmed yosryahmed@google.com --- mm/zswap.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/mm/zswap.c b/mm/zswap.c index 74411dfdad925..b6f4a1a760578 100644 --- a/mm/zswap.c +++ b/mm/zswap.c @@ -1105,6 +1105,8 @@ static int zswap_writeback_entry(struct zswap_entry *entry, if (zswap_rb_search(&tree->rbroot, swp_offset(entry->swpentry)) != entry) { spin_unlock(&tree->lock); delete_from_swap_cache(page_folio(page)); + unlock_page(page); + put_page(page); ret = -ENOMEM; goto fail; }