[PATCH v3 4/5] mm: shmem: only remove inode from swaplist when it's swapped page count is 0

[Kemeng Shi]

Even if we fail to allocate a swap entry, the inode might have previously
allocated entry and we might take inode containing swap entry off swaplist.
As a result, try_to_unuse() may enter a potential dead loop to repeatedly
look for inode and clean it's swap entry.
Only take inode off swaplist when it's swapped page count is 0 to fix the
issue.

Fixes: b487a2da3575b ("mm, swap: simplify folio swap allocation")
Signed-off-by: Kemeng Shi <shikemeng@xxxxxxxxxxxxxxx>
Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Reviewed-by: Kairui Song <kasong@xxxxxxxxxxx>
Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
Closes: https://lore.kernel.org/oe-lkp/202505161438.9009cf47-lkp@xxxxxxxxx
---
 mm/shmem.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index aeeddf612baa..07b8e1400c67 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1651,8 +1651,8 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)
 		BUG_ON(folio_mapped(folio));
 		return swap_writepage(&folio->page, wbc);
 	}
-
-	list_del_init(&info->swaplist);
+	if (!info->swapped)
+		list_del_init(&info->swaplist);
 	mutex_unlock(&shmem_swaplist_mutex);
 	if (nr_pages > 1)
 		goto try_split;
-- 
2.30.0