mm/huge_memory: fix rejection of swap cache folios with a mapping

A folio in the swap cache cannot be split if it has a mapping (shmem). 
The split code does a defensive check for this in
__folio_freeze_and_split_unmapped, after the folio ref has been frozen and
the NR_SHMEM_THPS/NR_FILE_THPS counters have been decremented.  It rejects
the split and returns -EINVAL without unfreezing the folio or restoring
the counters.

That error path is buggy, if it is ever taken.  It leaves the folio frozen
and stuck, skews the counters, and fires the VM_WARN_ON_ONCE_FOLIO for a
state that is actually legitimate.

Check for this case up front in folio_check_splittable and return -EBUSY
before any state is modified, so the split routine always backs out
cleanly.

Also fix a bracket style issue that checkpatch.pl keeps complaining about.

Link: https://lore.kernel.org/20260923-swap-thp-cleanup-v6-2-ba1b4ba72c6f@tencent.com
Fixes: 00527733d0dc ("mm/huge_memory: add two new (not yet used) functions for folio_split()")
Fixes: 714b056c8321 ("mm/huge_memory: convert VM_BUG* to VM_WARN* in __folio_split")
Signed-off-by: Kairui Song <kasong@tencent.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Barry Song <baohua@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Yeoreum Yun <yeoreum.yun@arm.com>
Reviewed-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Nico Pache <nico.pache@linux.dev>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Usama Arif <usama.arif@linux.dev>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Baoquan He <baoquan.he@linux.dev>
Cc: Youngjun Park <youngjun.park@lge.com>
Cc: Shivam Kalra <shivamkalra98@zohomail.in>
Cc: Kairui Song <ryncsn@gmail.com>

0 files changed, 0 insertions, 0 deletions