hugetlbfs: skip VMAs without shareable locks in hugetlb_vmdelete_list

hugetlb_vmdelete_list() uses trylock to acquire VMA locks during truncate
operations.  As per the original design in commit 40549ba8 ("hugetlb:
use new vma_lock for pmd sharing synchronization"), if the trylock fails
or the VMA has no lock, it should skip that VMA.  Any remaining mapped
pages are handled by remove_inode_hugepages() which is called after
hugetlb_vmdelete_list() and uses proper lock ordering to guarantee
unmapping success.

Currently, when hugetlb_vma_trylock_write() returns success (1) for VMAs
without shareable locks, the code proceeds to call unmap_hugepage_range().
This causes assertion failures in huge_pmd_unshare() →
hugetlb_vma_assert_locked() because no lock is actually held:

  WARNING: CPU: 1 PID: 6594 Comm: syz.0.28 Not tainted
  Call Trace:
   hugetlb_vma_assert_locked+0x1dd/0x250
   huge_pmd_unshare+0x2c8/0x540
   __unmap_hugepage_range+0x6e3/0x1aa0
   unmap_hugepage_range+0x32e/0x410
   hugetlb_vmdelete_list+0x189/0x1f0

Fix by using goto to ensure locks acquired by trylock are always released,
even when skipping VMAs without shareable locks.

Link: https://lkml.kernel.org/r/20250926033255.10930-1-kartikey406@gmail.com


Fixes: 40549ba8 ("hugetlb: use new vma_lock for pmd sharing synchronization")
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
Reported-by:  <syzbot+f26d7c75c26ec19790e7@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=f26d7c75c26ec19790e7


Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>