[PATCH v2 15/32] mm/userfaultfd: allow pte_offset_map_lock() to fail

Hugh Dickins
2023-06-09T01:26:13Z

mfill_atomic_install_pte() and mfill_atomic_pte_zeropage() treat
failed pte_offset_map_lock() as -EAGAIN, which mfill_atomic() already
returns to user for a similar race.

Signed-off-by: Hugh Dickins <hughd@google.com>
---
mm/userfaultfd.c | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index e97a0b4889fc..5fd787158c70 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -76,7 +76,10 @@ int mfill_atomic_install_pte(pmd_t *dst_pmd,
if (flags & MFILL_ATOMIC_WP)
_dst_pte = pte_mkuffd_wp(_dst_pte);

+ ret = -EAGAIN;
dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
+ if (!dst_pte)
+ goto out;

if (vma_is_shmem(dst_vma)) {
/* serialize against truncate with the page table lock */
@@ -121,6 +124,7 @@ int mfill_atomic_install_pte(pmd_t *dst_pmd,
ret = 0;
out_unlock:
pte_unmap_unlock(dst_pte, ptl);
+out:
return ret;
}

@@ -212,7 +216,10 @@ static int mfill_atomic_pte_zeropage(pmd_t *dst_pmd,

_dst_pte = pte_mkspecial(pfn_pte(my_zero_pfn(dst_addr),
dst_vma->vm_page_prot));
+ ret = -EAGAIN;
dst_pte = pte_offset_map_lock(dst_vma->vm_mm, dst_pmd, dst_addr, &ptl);
+ if (!dst_pte)
+ goto out;
if (dst_vma->vm_file) {
/* the shmem MAP_PRIVATE case requires checking the i_size */
inode = dst_vma->vm_file->f_inode;
@@ -231,6 +238,7 @@ static int mfill_atomic_pte_zeropage(pmd_t *dst_pmd,
ret = 0;
out_unlock:
pte_unmap_unlock(dst_pte, ptl);
+out:
return ret;
}

--
2.35.3