Re: [PATCH 1/2] mm: replace BUG_ON in vm_insert_page with a return of an error

[Miaohe Lin <linmiaohe@huawei.com>]

Hi:
On 2021/2/3 8:31, Suren Baghdasaryan wrote:
> Replace BUG_ON(vma->vm_flags & VM_PFNMAP) in vm_insert_page with
> WARN_ON_ONCE and returning an error. This is to ensure users of the
> vm_insert_page that set VM_PFNMAP are notified of the wrong flag usage
> and get an indication of an error without panicing the kernel.
> This will help identifying drivers that need to clear VM_PFNMAP before
> using dmabuf system heap which is moving to use vm_insert_page.
> 
> Suggested-by: Christoph Hellwig <hch@infradead.org>
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>

Looks reasonable. Thanks.
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>

> ---
>  mm/memory.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index feff48e1465a..e503c9801cd9 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -1827,7 +1827,8 @@ int vm_insert_page(struct vm_area_struct *vma, unsigned long addr,
>  		return -EINVAL;
>  	if (!(vma->vm_flags & VM_MIXEDMAP)) {
>  		BUG_ON(mmap_read_trylock(vma->vm_mm));
> -		BUG_ON(vma->vm_flags & VM_PFNMAP);
> +		if (WARN_ON_ONCE(vma->vm_flags & VM_PFNMAP))
> +			return -EINVAL;
>  		vma->vm_flags |= VM_MIXEDMAP;
>  	}
>  	return insert_page(vma, addr, page, vma->vm_page_prot);
>