On Mon, Mar 03, 2025 at 11:08:34AM +0000, Lorenzo Stoakes wrote:
> Update move_vma() to use the threaded VRM object, de-duplicate code and
> separate into smaller functions to aid readability and debug-ability.
>
> This in turn allows further simplification of expand_vma() as we can simply
> thread VRM through the function.
>
> We also take the opportunity to abstract the account charging page count
> into the VRM in order that we can correctly thread this through the
> operation.
>
> We additionally do the same for tracking mm statistics - exec_vm, stack_vm,
> data_vm, and locked_vm.
>
> As part of this change, we slightly modify when locked pages statistics are
> counted for in mm_struct statistics. However this should cause no issues,
> as there is no chance of underflow, nor will any rlimit failures occur as a
> result.
>
> This is an intermediate step before a further refactoring of move_vma() in
> order to aid review.
>
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
> ---
[..]
> +/*
> + * Perform checks before attempting to write a VMA prior to it being
> + * moved.
> + */
> +static unsigned long prep_move_vma(struct vma_remap_struct *vrm,
> + unsigned long *vm_flags_ptr)
> +{
> + unsigned long err;
I am getting a warning on mm-unstable because 'err' is sometimes used
uninitialized, I think here:
if (vma->vm_ops && vma->vm_ops->may_split) {
if (vma->vm_start != old_addr)
err = vma->vm_ops->may_split(vma, old_addr);
if (!err && vma->vm_end != old_addr + old_len)
err = vma->vm_ops->may_split(vma, old_addr + old_len);
if (err)
return err;
}
> + struct vm_area_struct *vma = vrm->vma;
> + unsigned long old_addr = vrm->addr;
> + unsigned long old_len = vrm->old_len;
>
> /*
> * We'd prefer to avoid failure later on in do_munmap:
> * which may split one vma into three before unmapping.
> */
> - if (mm->map_count >= sysctl_max_map_count - 3)
> + if (current->mm->map_count >= sysctl_max_map_count - 3)
> return -ENOMEM;
>
> - if (unlikely(flags & MREMAP_DONTUNMAP))
> - to_account = new_len;
> -
> if (vma->vm_ops && vma->vm_ops->may_split) {
> if (vma->vm_start != old_addr)
> err = vma->vm_ops->may_split(vma, old_addr);
[..]
