diff mbox series

[09/31] mm/pagewalkers: ACTION_AGAIN if pte_offset_map_lock() fails

Message ID 6265ac58-6018-a8c6-cf38-69cba698471@google.com
State New
Headers
Series mm: allow pte_offset_map[_lock]() to fail |

Commit Message

Hugh Dickins May 22, 2023, 5 a.m. UTC 
  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>
---
 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(-)

Comments

SeongJae Park May 23, 2023, 6:07 p.m. UTC | #1 
Hello Hugh,

On Sun, 21 May 2023 22:00:15 -0700 (PDT) Hugh Dickins <hughd@google.com> wrote:

> 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>

For below mm/damon part,

Reviewed-by: SeongJae Park <sj@kernel.org>


Thanks,
SJ

> ---
>  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/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 mbox series

Patch

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;