mm: shmem: only remove inode from swaplist when it's swapped page count is 0

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.

Link: https://lkml.kernel.org/r/20250516170939.965736-5-shikemeng@huaweicloud.com
Fixes: b487a2da3575 ("mm, swap: simplify folio swap allocation")
Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Kairui Song <kasong@tencent.com>
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202505161438.9009cf47-lkp@intel.com
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/shmem.c b/mm/shmem.c
index aeeddf612baa842bd7ad2e656e73f78e235aeed3..07b8e1400c67a542e9d53039f15cdb2bd34f1d32 100644 (file)
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1651,8 +1651,8 @@ try_split:
                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;