linux-kernel - Re: [PATCH v9 16/17] mm: make vma cache SLAB_TYPESAFE_BY

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Message-ID: <CAJuCfpGShzXxqH8up75WQhdMzkr+Y6eE-h37nEEwVWHC6AN89w@mail.gmail.com>
Date: Tue, 14 Jan 2025 19:15:05 -0800
From: Suren Baghdasaryan <surenb@...gle.com>
To: Wei Yang <richard.weiyang@...il.com>
Cc: akpm@...ux-foundation.org, peterz@...radead.org, willy@...radead.org, 
	liam.howlett@...cle.com, lorenzo.stoakes@...cle.com, 
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Subject: Re: [PATCH v9 16/17] mm: make vma cache SLAB_TYPESAFE_BY_RCU

On Tue, Jan 14, 2025 at 6:27 PM Wei Yang <richard.weiyang@...il.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