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Date:   Tue, 2 Feb 2021 17:31:03 -0800
From:   Minchan Kim <minchan@...nel.org>
To:     Suren Baghdasaryan <surenb@...gle.com>
Cc:     sumit.semwal@...aro.org, akpm@...ux-foundation.org,
        hch@...radead.org, lmark@...eaurora.org, labbott@...hat.com,
        Brian.Starkey@....com, john.stultz@...aro.org,
        christian.koenig@....com, cgoldswo@...eaurora.org,
        orjan.eide@....com, robin.murphy@....com, jajones@...dia.com,
        hridya@...gle.com, sspatil@...gle.com, linux-media@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kernel-team@...roid.com
Subject: Re: [PATCH 1/2] mm: replace BUG_ON in vm_insert_page with a return
 of an error

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@...radead.org>
> Signed-off-by: Suren Baghdasaryan <surenb@...gle.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?

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