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

["Lorenzo Stoakes (Oracle)" <ljs@kernel.org>]

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
>