mm: shmem: avoid unpaired folio_unlock() in shmem_swapin_folio()

Patch series "Some random fixes and cleanup to shmem", v3.

This series contains some simple fixes and cleanup which are made during
learning shmem.  More details can be found in respective patches.


This patch (of 5):

If we get a folio from swap_cache_get_folio() successfully but encounter a
failure before the folio is locked, we will unlock the folio which was not
previously locked.

Put the folio and set it to NULL when a failure occurs before the folio is
locked to fix the issue.

Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Fixes: 0583135 ("mm: shmem: fix potential data corruption during shmem swapin")
Signed-off-by: Kemeng Shi <[email protected]>
Reviewed-by: Baolin Wang <[email protected]>
Reviewed-by: Kairui Song <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: kernel test robot <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: Kemeng Shi

mm/shmem.c

@@ -2335,6 +2335,8 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
 		 */
 		split_order = shmem_split_large_entry(inode, index, swap, gfp);
 		if (split_order < 0) {
+			folio_put(folio);
+			folio = NULL;
 			error = split_order;
 			goto failed;
 		}