mm: zswap: fix missing folio cleanup in writeback race path

commit e3b63e966cac0bf78aaa1efede1827a252815a1d upstream.

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>
Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/mm/zswap.c b/mm/zswap.c
index b3829ada4a413e87f50bbfe5e5238776a3840a9c..b7cb126797f9e3f8375833ccf4c23a9632d409a6 100644 (file)
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -1013,6 +1013,8 @@ static int zswap_writeback_entry(struct zpool *pool, unsigned long handle)
                if (zswap_rb_search(&tree->rbroot, entry->offset) != entry) {
                        spin_unlock(&tree->lock);
                        delete_from_swap_cache(page_folio(page));
+                       unlock_page(page);
+                       put_page(page);
                        ret = -ENOMEM;
                        goto fail;
                }