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Sender: Minchan Kim <minchan.kim@gmail.com>
Date:   Tue, 2 Feb 2021 17:31:03 -0800
From:   Minchan Kim <minchan@kernel.org>
To:     Suren Baghdasaryan <surenb@google.com>
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Subject: Re: [PATCH 1/2] mm: replace BUG_ON in vm_insert_page with a return
 of an error
Message-ID: <YBn81xAeCqHgudYb@google.com>
References: <20210203003134.2422308-1-surenb@google.com>
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On Tue, Feb 02, 2021 at 04:31:33PM -0800, 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>
> ---
>  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));

Better to replace above BUG_ON with WARN_ON_ONCE, too?