Re: [PATCH v6 5/6] mm: use vma_start_write_killable() in process_vma_walk_lock()

Lorenzo Stoakes (Oracle)
2026-03-31T10:39:04Z

On Fri, Mar 27, 2026 at 01:54:56PM -0700, Suren Baghdasaryan wrote:
> Replace vma_start_write() with vma_start_write_killable() when
> process_vma_walk_lock() is used with PGWALK_WRLOCK option.
> Adjust its direct and indirect users to check for a possible error
> and handle it. Ensure users handle EINTR correctly and do not ignore
> it. When queue_pages_range() fails, check whether it failed due to
> a fatal signal or some other reason and return appropriate error.
>
> Suggested-by: Matthew Wilcox <willy@infradead.org>
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> ---
> fs/proc/task_mmu.c | 12 ++++++------
> mm/mempolicy.c | 10 +++++++++-
> mm/pagewalk.c | 22 +++++++++++++++-------
> 3 files changed, 30 insertions(+), 14 deletions(-)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index e091931d7ca1..33e5094a7842 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -1774,15 +1774,15 @@ static ssize_t clear_refs_write(struct file *file, const char __user *buf,
> struct vm_area_struct *vma;
> enum clear_refs_types type;
> int itype;
> - int rv;
> + int err;
>
> if (count > sizeof(buffer) - 1)
> count = sizeof(buffer) - 1;
> if (copy_from_user(buffer, buf, count))
> return -EFAULT;
> - rv = kstrtoint(strstrip(buffer), 10, &itype);
> - if (rv < 0)
> - return rv;
> + err = kstrtoint(strstrip(buffer), 10, &itype);
> + if (err)
> + return err;
> type = (enum clear_refs_types)itype;
> if (type < CLEAR_REFS_ALL || type >= CLEAR_REFS_LAST)
> return -EINVAL;
> @@ -1824,7 +1824,7 @@ static ssize_t clear_refs_write(struct file *file, const char __user *buf,
> 0, mm, 0, -1UL);
> mmu_notifier_invalidate_range_start(&range);
> }
> - walk_page_range(mm, 0, -1, &clear_refs_walk_ops, &cp);
> + err = walk_page_range(mm, 0, -1, &clear_refs_walk_ops, &cp);
> if (type == CLEAR_REFS_SOFT_DIRTY) {
> mmu_notifier_invalidate_range_end(&range);
> flush_tlb_mm(mm);
> @@ -1837,7 +1837,7 @@ static ssize_t clear_refs_write(struct file *file, const char __user *buf,
> }
> put_task_struct(task);
>
> - return count;
> + return err ? : count;
> }
>
> const struct file_operations proc_clear_refs_operations = {
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index c38a90487531..51f298cfc33b 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -969,6 +969,7 @@ static const struct mm_walk_ops queue_pages_lock_vma_walk_ops = {
> * (a hugetlbfs page or a transparent huge page being counted as 1).
> * -EIO - a misplaced page found, when MPOL_MF_STRICT specified without MOVEs.
> * -EFAULT - a hole in the memory range, when MPOL_MF_DISCONTIG_OK unspecified.
> + * -EINTR - walk got terminated due to pending fatal signal.
> */
> static long
> queue_pages_range(struct mm_struct *mm, unsigned long start, unsigned long end,
> @@ -1545,7 +1546,14 @@ static long do_mbind(unsigned long start, unsigned long len,
> flags | MPOL_MF_INVERT | MPOL_MF_WRLOCK, &pagelist);
>
> if (nr_failed < 0) {
> - err = nr_failed;
> + /*
> + * queue_pages_range() might override the original error with -EFAULT.
> + * Confirm that fatal signals are still treated correctly.
> + */
> + if (fatal_signal_pending(current))
> + err = -EINTR;
> + else
> + err = nr_failed;

Is that really a big deal? Does it really matter if the caller doesn't get
-EINTR in this case? This feels like another sashiko nitpick and is adding a
bunch of additional complexity here.

I mean if you 'filter' error messages you might always end up with an error
that's different than the original...

> nr_failed = 0;
> } else {
> vma_iter_init(&vmi, mm, start);
> diff --git a/mm/pagewalk.c b/mm/pagewalk.c
> index 3ae2586ff45b..eca7bc711617 100644
> --- a/mm/pagewalk.c
> +++ b/mm/pagewalk.c
> @@ -443,14 +443,13 @@ static inline void process_mm_walk_lock(struct mm_struct *mm,
> mmap_assert_write_locked(mm);
> }
>
> -static inline void process_vma_walk_lock(struct vm_area_struct *vma,
> - enum page_walk_lock walk_lock)
> +static int process_vma_walk_lock(struct vm_area_struct *vma,
> + enum page_walk_lock walk_lock)
> {
> #ifdef CONFIG_PER_VMA_LOCK
> switch (walk_lock) {
> case PGWALK_WRLOCK:
> - vma_start_write(vma);
> - break;
> + return vma_start_write_killable(vma);
> case PGWALK_WRLOCK_VERIFY:
> vma_assert_write_locked(vma);
> break;
> @@ -462,6 +461,7 @@ static inline void process_vma_walk_lock(struct vm_area_struct *vma,
> break;
> }
> #endif
> + return 0;
> }
>
> /*
> @@ -505,7 +505,9 @@ int walk_page_range_mm_unsafe(struct mm_struct *mm, unsigned long start,
> if (ops->pte_hole)
> err = ops->pte_hole(start, next, -1, &walk);
> } else { /* inside vma */
> - process_vma_walk_lock(vma, ops->walk_lock);
> + err = process_vma_walk_lock(vma, ops->walk_lock);
> + if (err)
> + break;
> walk.vma = vma;
> next = min(end, vma->vm_end);
> vma = find_vma(mm, vma->vm_end);
> @@ -722,6 +724,7 @@ int walk_page_range_vma_unsafe(struct vm_area_struct *vma, unsigned long start,
> .vma = vma,
> .private = private,
> };
> + int err;
>
> if (start >= end || !walk.mm)
> return -EINVAL;
> @@ -729,7 +732,9 @@ int walk_page_range_vma_unsafe(struct vm_area_struct *vma, unsigned long start,
> return -EINVAL;
>
> process_mm_walk_lock(walk.mm, ops->walk_lock);
> - process_vma_walk_lock(vma, ops->walk_lock);
> + err = process_vma_walk_lock(vma, ops->walk_lock);
> + if (err)
> + return err;
> return __walk_page_range(start, end, &walk);
> }
>
> @@ -752,6 +757,7 @@ int walk_page_vma(struct vm_area_struct *vma, const struct mm_walk_ops *ops,
> .vma = vma,
> .private = private,
> };
> + int err;
>
> if (!walk.mm)
> return -EINVAL;
> @@ -759,7 +765,9 @@ int walk_page_vma(struct vm_area_struct *vma, const struct mm_walk_ops *ops,
> return -EINVAL;
>
> process_mm_walk_lock(walk.mm, ops->walk_lock);
> - process_vma_walk_lock(vma, ops->walk_lock);
> + err = process_vma_walk_lock(vma, ops->walk_lock);
> + if (err)
> + return err;
> return __walk_page_range(vma->vm_start, vma->vm_end, &walk);
> }
>
> --
> 2.53.0.1018.g2bb0e51243-goog
>