[PATCH v2 22/32] mm/swapoff: allow pte_offset_map[_lock]() to fail

Hugh Dickins
2023-06-09T01:36:19Z

Adjust unuse_pte() and unuse_pte_range() to allow pte_offset_map_lock()
and pte_offset_map() failure; remove pmd_none_or_trans_huge_or_clear_bad()
from unuse_pmd_range() now that pte_offset_map() does all that itself.

Signed-off-by: Hugh Dickins <hughd@google.com>
---
mm/swapfile.c | 38 ++++++++++++++++++++------------------
1 file changed, 20 insertions(+), 18 deletions(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 274bbf797480..12d204e6dae2 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1774,7 +1774,7 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
hwposioned = true;

pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
- if (unlikely(!pte_same_as_swp(*pte, swp_entry_to_pte(entry)))) {
+ if (unlikely(!pte || !pte_same_as_swp(*pte, swp_entry_to_pte(entry)))) {
ret = 0;
goto out;
}
@@ -1827,7 +1827,8 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
set_pte_at(vma->vm_mm, addr, pte, new_pte);
swap_free(entry);
out:
- pte_unmap_unlock(pte, ptl);
+ if (pte)
+ pte_unmap_unlock(pte, ptl);
if (page != swapcache) {
unlock_page(page);
put_page(page);
@@ -1839,17 +1840,22 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
unsigned long addr, unsigned long end,
unsigned int type)
{
- swp_entry_t entry;
- pte_t *pte;
+ pte_t *pte = NULL;
struct swap_info_struct *si;
- int ret = 0;

si = swap_info[type];
- pte = pte_offset_map(pmd, addr);
do {
struct folio *folio;
unsigned long offset;
unsigned char swp_count;
+ swp_entry_t entry;
+ int ret;
+
+ if (!pte++) {
+ pte = pte_offset_map(pmd, addr);
+ if (!pte)
+ break;
+ }

if (!is_swap_pte(*pte))
continue;
@@ -1860,6 +1866,8 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,

offset = swp_offset(entry);
pte_unmap(pte);
+ pte = NULL;
+
folio = swap_cache_get_folio(entry, vma, addr);
if (!folio) {
struct page *page;
@@ -1878,8 +1886,7 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
if (!folio) {
swp_count = READ_ONCE(si->swap_map[offset]);
if (swp_count == 0 || swp_count == SWAP_MAP_BAD)
- goto try_next;
-
+ continue;
return -ENOMEM;
}

@@ -1889,20 +1896,17 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
if (ret < 0) {
folio_unlock(folio);
folio_put(folio);
- goto out;
+ return ret;
}

folio_free_swap(folio);
folio_unlock(folio);
folio_put(folio);
-try_next:
- pte = pte_offset_map(pmd, addr);
- } while (pte++, addr += PAGE_SIZE, addr != end);
- pte_unmap(pte - 1);
+ } while (addr += PAGE_SIZE, addr != end);

- ret = 0;
-out:
- return ret;
+ if (pte)
+ pte_unmap(pte);
+ return 0;
}

static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud,
@@ -1917,8 +1921,6 @@ static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud,
do {
cond_resched();
next = pmd_addr_end(addr, end);
- if (pmd_none_or_trans_huge_or_clear_bad(pmd))
- continue;
ret = unuse_pte_range(vma, pmd, addr, next, type);
if (ret)
return ret;
--
2.35.3