mm/hmm: do not call hmm_vma_walk_hole() while holding a spinlock

This eventually calls into handle_mm_fault() which is a sleeping function.
Release the lock first.

hmm_vma_walk_hole() does not touch the contents of the PUD, so it does not
need the lock.

Fixes: 3afc4236 ("mm: pagewalk: add p4d_entry() and pgd_entry()")
Cc: Steven Price <steven.price@arm.com>
Reviewed-by: Ralph Campbell <rcampbell@nvidia.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

mm/hmm.c

@@ -491,8 +491,8 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end,
 
 	pud = READ_ONCE(*pudp);
 	if (pud_none(pud)) {
-		ret = hmm_vma_walk_hole(start, end, -1, walk);
-		goto out_unlock;
+		spin_unlock(ptl);
+		return hmm_vma_walk_hole(start, end, -1, walk);
 	}
 
 	if (pud_huge(pud) && pud_devmap(pud)) {
@@ -501,8 +501,8 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end,
 		bool fault, write_fault;
 
 		if (!pud_present(pud)) {
-			ret = hmm_vma_walk_hole(start, end, -1, walk);
-			goto out_unlock;
+			spin_unlock(ptl);
+			return hmm_vma_walk_hole(start, end, -1, walk);
 		}
 
 		i = (addr - range->start) >> PAGE_SHIFT;
@@ -513,9 +513,9 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end,
 		hmm_range_need_fault(hmm_vma_walk, pfns, npages,
 				     cpu_flags, &fault, &write_fault);
 		if (fault || write_fault) {
-			ret = hmm_vma_walk_hole_(addr, end, fault,
-						 write_fault, walk);
-			goto out_unlock;
+			spin_unlock(ptl);
+			return hmm_vma_walk_hole_(addr, end, fault, write_fault,
+						  walk);
 		}
 
 		pfn = pud_pfn(pud) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);