[PATCH v2 09/32] mm/pagewalkers: ACTION_AGAIN if pte_offset_map_lock() fails

Hugh Dickins
2023-06-09T01:17:35Z

Simple walk_page_range() users should set ACTION_AGAIN to retry when
pte_offset_map_lock() fails.

No need to check pmd_trans_unstable(): that was precisely to avoid the
possiblity of calling pte_offset_map() on a racily removed or inserted
THP entry, but such cases are now safely handled inside it. Likewise
there is no need to check pmd_none() or pmd_bad() before calling it.

Signed-off-by: Hugh Dickins <hughd@google.com>
Reviewed-by: SeongJae Park <sj@kernel.org> for mm/damon part
---
fs/proc/task_mmu.c | 32 ++++++++++++++++----------------
mm/damon/vaddr.c | 12 ++++++++----
mm/mempolicy.c | 7 ++++---
mm/mincore.c | 9 ++++-----
mm/mlock.c | 4 ++++
5 files changed, 36 insertions(+), 28 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 420510f6a545..dba5052ce09b 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -631,14 +631,11 @@ static int smaps_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
goto out;
}

- if (pmd_trans_unstable(pmd))
- goto out;
- /*
- * The mmap_lock held all the way back in m_start() is what
- * keeps khugepaged out of here and from collapsing things
- * in here.
- */
pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
+ if (!pte) {
+ walk->action = ACTION_AGAIN;
+ return 0;
+ }
for (; addr != end; pte++, addr += PAGE_SIZE)
smaps_pte_entry(pte, addr, walk);
pte_unmap_unlock(pte - 1, ptl);
@@ -1191,10 +1188,11 @@ static int clear_refs_pte_range(pmd_t *pmd, unsigned long addr,
return 0;
}

- if (pmd_trans_unstable(pmd))
- return 0;
-
pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
+ if (!pte) {
+ walk->action = ACTION_AGAIN;
+ return 0;
+ }
for (; addr != end; pte++, addr += PAGE_SIZE) {
ptent = *pte;

@@ -1538,9 +1536,6 @@ static int pagemap_pmd_range(pmd_t *pmdp, unsigned long addr, unsigned long end,
spin_unlock(ptl);
return err;
}
-
- if (pmd_trans_unstable(pmdp))
- return 0;
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */

/*
@@ -1548,6 +1543,10 @@ static int pagemap_pmd_range(pmd_t *pmdp, unsigned long addr, unsigned long end,
* goes beyond vma->vm_end.
*/
orig_pte = pte = pte_offset_map_lock(walk->mm, pmdp, addr, &ptl);
+ if (!pte) {
+ walk->action = ACTION_AGAIN;
+ return err;
+ }
for (; addr < end; pte++, addr += PAGE_SIZE) {
pagemap_entry_t pme;

@@ -1887,11 +1886,12 @@ static int gather_pte_stats(pmd_t *pmd, unsigned long addr,
spin_unlock(ptl);
return 0;
}
-
- if (pmd_trans_unstable(pmd))
- return 0;
#endif
orig_pte = pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
+ if (!pte) {
+ walk->action = ACTION_AGAIN;
+ return 0;
+ }
do {
struct page *page = can_gather_numa_stats(*pte, vma, addr);
if (!page)
diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c
index 1fec16d7263e..b8762ff15c3c 100644
--- a/mm/damon/vaddr.c
+++ b/mm/damon/vaddr.c
@@ -318,9 +318,11 @@ static int damon_mkold_pmd_entry(pmd_t *pmd, unsigned long addr,
spin_unlock(ptl);
}

- if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
- return 0;
pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
+ if (!pte) {
+ walk->action = ACTION_AGAIN;
+ return 0;
+ }
if (!pte_present(*pte))
goto out;
damon_ptep_mkold(pte, walk->mm, addr);
@@ -464,9 +466,11 @@ static int damon_young_pmd_entry(pmd_t *pmd, unsigned long addr,
regular_page:
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */

- if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
- return -EINVAL;
pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
+ if (!pte) {
+ walk->action = ACTION_AGAIN;
+ return 0;
+ }
if (!pte_present(*pte))
goto out;
folio = damon_get_folio(pte_pfn(*pte));
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 1756389a0609..4d0bcf6f0d52 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -514,10 +514,11 @@ static int queue_folios_pte_range(pmd_t *pmd, unsigned long addr,
if (ptl)
return queue_folios_pmd(pmd, ptl, addr, end, walk);

- if (pmd_trans_unstable(pmd))
- return 0;
-
mapped_pte = pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
+ if (!pte) {
+ walk->action = ACTION_AGAIN;
+ return 0;
+ }
for (; addr != end; pte++, addr += PAGE_SIZE) {
if (!pte_present(*pte))
continue;
diff --git a/mm/mincore.c b/mm/mincore.c
index 2d5be013a25a..f33f6a0b1ded 100644
--- a/mm/mincore.c
+++ b/mm/mincore.c
@@ -113,12 +113,11 @@ static int mincore_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
goto out;
}

- if (pmd_trans_unstable(pmd)) {
- __mincore_unmapped_range(addr, end, vma, vec);
- goto out;
- }
-
ptep = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
+ if (!ptep) {
+ walk->action = ACTION_AGAIN;
+ return 0;
+ }
for (; addr != end; ptep++, addr += PAGE_SIZE) {
pte_t pte = *ptep;

diff --git a/mm/mlock.c b/mm/mlock.c
index 40b43f8740df..9f2b1173b1b1 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -329,6 +329,10 @@ static int mlock_pte_range(pmd_t *pmd, unsigned long addr,
}

start_pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
+ if (!start_pte) {
+ walk->action = ACTION_AGAIN;
+ return 0;
+ }
for (pte = start_pte; addr != end; pte++, addr += PAGE_SIZE) {
if (!pte_present(*pte))
continue;
--
2.35.3