Re: [PATCH v9 16/17] mm: make vma cache SLAB_TYPESAFE_BY_RCU

Suren Baghdasaryan
2025-01-15T03:15:17Z

On Tue, Jan 14, 2025 at 6:27 PM Wei Yang <richard.weiyang@gmail.com> wrote:
>
> On Fri, Jan 10, 2025 at 08:26:03PM -0800, Suren Baghdasaryan wrote:
>
> >diff --git a/kernel/fork.c b/kernel/fork.c
> >index 9d9275783cf8..151b40627c14 100644
> >--- a/kernel/fork.c
> >+++ b/kernel/fork.c
> >@@ -449,6 +449,42 @@ struct vm_area_struct *vm_area_alloc(struct mm_struct *mm)
> > return vma;
> > }
> >
> >+static void vm_area_init_from(const struct vm_area_struct *src,
> >+ struct vm_area_struct *dest)
> >+{
> >+ dest->vm_mm = src->vm_mm;
> >+ dest->vm_ops = src->vm_ops;
> >+ dest->vm_start = src->vm_start;
> >+ dest->vm_end = src->vm_end;
> >+ dest->anon_vma = src->anon_vma;
> >+ dest->vm_pgoff = src->vm_pgoff;
> >+ dest->vm_file = src->vm_file;
> >+ dest->vm_private_data = src->vm_private_data;
> >+ vm_flags_init(dest, src->vm_flags);
> >+ memcpy(&dest->vm_page_prot, &src->vm_page_prot,
> >+ sizeof(dest->vm_page_prot));
> >+ /*
> >+ * src->shared.rb may be modified concurrently when called from
> >+ * dup_mmap(), but the clone will reinitialize it.
> >+ */
> >+ data_race(memcpy(&dest->shared, &src->shared, sizeof(dest->shared)));
> >+ memcpy(&dest->vm_userfaultfd_ctx, &src->vm_userfaultfd_ctx,
> >+ sizeof(dest->vm_userfaultfd_ctx));
> >+#ifdef CONFIG_ANON_VMA_NAME
> >+ dest->anon_name = src->anon_name;
> >+#endif
> >+#ifdef CONFIG_SWAP
> >+ memcpy(&dest->swap_readahead_info, &src->swap_readahead_info,
> >+ sizeof(dest->swap_readahead_info));
> >+#endif
> >+#ifndef CONFIG_MMU
> >+ dest->vm_region = src->vm_region;
> >+#endif
> >+#ifdef CONFIG_NUMA
> >+ dest->vm_policy = src->vm_policy;
> >+#endif
> >+}
>
> Would this be difficult to maintain? We should make sure not miss or overwrite
> anything.

Yeah, it is less maintainable than a simple memcpy() but I did not
find a better alternative. I added a warning above the struct
vm_area_struct definition to update this function every time we change
that structure. Not sure if there is anything else I can do to help
with this.

>
> --
> Wei Yang
> Help you, Help me