linux-kernel - Re: [PATCH 2/2] mm/hmm: hmm_range

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Message-ID: <20190827184157.GA24929@ziepe.ca>
Date:   Tue, 27 Aug 2019 15:41:57 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Ralph Campbell <rcampbell@...dia.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        nouveau@...ts.freedesktop.org,
        Jérôme Glisse <jglisse@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH 2/2] mm/hmm: hmm_range_fault() infinite loop

On Fri, Aug 23, 2019 at 03:17:53PM -0700, Ralph Campbell wrote:

> Signed-off-by: Ralph Campbell <rcampbell@...dia.com>
>  mm/hmm.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/mm/hmm.c b/mm/hmm.c
> index 29371485fe94..4882b83aeccb 100644
> +++ b/mm/hmm.c
> @@ -292,6 +292,9 @@ static int hmm_vma_walk_hole_(unsigned long addr, unsigned long end,
>  	hmm_vma_walk->last = addr;
>  	i = (addr - range->start) >> PAGE_SHIFT;
>  
> +	if (write_fault && walk->vma && !(walk->vma->vm_flags & VM_WRITE))
> +		return -EPERM;

Can walk->vma be NULL here? hmm_vma_do_fault() touches it
unconditionally.

Jason