[PATCH v4 7/9] mm/hugetlb: Make follow_hugetlb_page() safe to pmd unshare

Peter Xu
2022-12-16T15:52:31Z

Since follow_hugetlb_page() walks the pgtable, it needs the vma lock
to make sure the pgtable page will not be freed concurrently.

Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
mm/hugetlb.c | 7 +++++++
1 file changed, 7 insertions(+)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 0bf0abea388d..33fe73e1e589 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -6433,6 +6433,7 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
break;
}

+ hugetlb_vma_lock_read(vma);
/*
* Some archs (sparc64, sh*) have multiple pte_ts to
* each hugepage. We have to make sure we get the
@@ -6457,6 +6458,7 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
!hugetlbfs_pagecache_present(h, vma, vaddr)) {
if (pte)
spin_unlock(ptl);
+ hugetlb_vma_unlock_read(vma);
remainder = 0;
break;
}
@@ -6478,6 +6480,8 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,

if (pte)
spin_unlock(ptl);
+ hugetlb_vma_unlock_read(vma);
+
if (flags & FOLL_WRITE)
fault_flags |= FAULT_FLAG_WRITE;
else if (unshare)
@@ -6540,6 +6544,7 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
remainder -= pages_per_huge_page(h);
i += pages_per_huge_page(h);
spin_unlock(ptl);
+ hugetlb_vma_unlock_read(vma);
continue;
}

@@ -6569,6 +6574,7 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
if (WARN_ON_ONCE(!try_grab_folio(pages[i], refs,
flags))) {
spin_unlock(ptl);
+ hugetlb_vma_unlock_read(vma);
remainder = 0;
err = -ENOMEM;
break;
@@ -6580,6 +6586,7 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
i += refs;

spin_unlock(ptl);
+ hugetlb_vma_unlock_read(vma);
}
*nr_pages = remainder;
/*
--
2.37.3