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

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

commit e08d5f515613a9860bfee7312461a19f422adb5e upstream.

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/20250516170939.965736-1-shikemeng@huaweicloud.com
Link: https://lkml.kernel.org/r/20250516170939.965736-2-shikemeng@huaweicloud.com
Fixes: 058313515d5a ("mm: shmem: fix potential data corruption during shmem swapin")
Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Kairui Song <kasong@tencent.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: kernel test robot <oliver.sang@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
[ hughd: removed series cover letter comments ]
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>