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 40549ba8f8e0 ("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: 40549ba8f8e0 ("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>

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 3cfdf4091001f83d1f8a984d3018a877bde5caee..94b4d854429e5531858677d1c3cef039fc545f9b 100644 (file)
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -478,6 +478,14 @@ hugetlb_vmdelete_list(struct rb_root_cached *root, pgoff_t start, pgoff_t end,
                if (!hugetlb_vma_trylock_write(vma))
                        continue;
 
+               /*
+                * Skip VMAs without shareable locks. Per the design in commit
+                * 40549ba8f8e0, these will be handled by remove_inode_hugepages()
+                * called after this function with proper locking.
+                */
+               if (!__vma_shareable_lock(vma))
+                       goto skip;
+
                v_start = vma_offset_start(vma, start);
                v_end = vma_offset_end(vma, end);
 
@@ -488,6 +496,7 @@ hugetlb_vmdelete_list(struct rb_root_cached *root, pgoff_t start, pgoff_t end,
                 * vmas.  Therefore, lock is not held when calling
                 * unmap_hugepage_range for private vmas.
                 */
+skip:
                hugetlb_vma_unlock_write(vma);
        }
 }