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Subject: Re: [PATCH 1/2] mm: replace BUG_ON in vm_insert_page with a return of
 an error
To:     Suren Baghdasaryan <surenb@google.com>, <sumit.semwal@linaro.org>
CC:     <akpm@linux-foundation.org>, <hch@infradead.org>,
        <lmark@codeaurora.org>, <labbott@redhat.com>,
        <Brian.Starkey@arm.com>, <john.stultz@linaro.org>,
        <christian.koenig@amd.com>, <cgoldswo@codeaurora.org>,
        <orjan.eide@arm.com>, <robin.murphy@arm.com>, <jajones@nvidia.com>,
        <minchan@kernel.org>, <hridya@google.com>, <sspatil@google.com>,
        <linux-media@vger.kernel.org>, <dri-devel@lists.freedesktop.org>,
        <linaro-mm-sig@lists.linaro.org>, <linux-mm@kvack.org>,
        <linux-kernel@vger.kernel.org>, <kernel-team@android.com>
References: <20210203003134.2422308-1-surenb@google.com>
From:   Miaohe Lin <linmiaohe@huawei.com>
Message-ID: <a2376ae0-c6a2-12e4-d4ad-04696eb51535@huawei.com>
Date:   Wed, 3 Feb 2021 09:27:04 +0800
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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);
>