[PATCH v3 6/7] mm/memfd_luo: remove folio from page cache when accounting fails

[Chenghao Duan <duanchenghao@kylinos.cn>]

In memfd_luo_retrieve_folios(), when shmem_inode_acct_blocks() fails
after successfully adding the folio to the page cache, the code jumps
to unlock_folio without removing the folio from the page cache.

This leaves the folio permanently abandoned in the page cache:
- The folio was added via shmem_add_to_page_cache() which set up
  mapping, index, and incremented nrpages/shmem stats.
- folio_unlock() and folio_put() do not remove it from the cache.
- folio_add_lru() was never called, so it cannot be reclaimed.

Fix by adding a remove_from_cache label that calls filemap_remove_folio()
before unlocking, matching the error handling pattern in
shmem_alloc_and_add_folio().

This issue was identified by the AI review.
https://sashiko.dev/#/patchset/20260323110747.193569-1-duanchenghao@kylinos.cn

Signed-off-by: Chenghao Duan <duanchenghao@kylinos.cn>
---
 mm/memfd_luo.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/memfd_luo.c b/mm/memfd_luo.c
index b4cea3670689..f8e8f99b1848 100644
--- a/mm/memfd_luo.c
+++ b/mm/memfd_luo.c
@@ -446,7 +446,7 @@ static int memfd_luo_retrieve_folios(struct file *file,
 		if (err) {
 			pr_err("shmem: failed to account folio index %ld(%ld pages): %d\n",
 			       i, npages, err);
-			goto unlock_folio;
+			goto remove_from_cache;
 		}
 
 		nr_added_pages += npages;
@@ -459,6 +459,8 @@ static int memfd_luo_retrieve_folios(struct file *file,
 
 	return 0;
 
+remove_from_cache:
+	filemap_remove_folio(folio);
 unlock_folio:
 	folio_unlock(folio);
 	folio_put(folio);
-- 
2.25.1