Re: [PATCH 2/2] mm/hmm: hmm_range_fault() infinite loop

From: Jason Gunthorpe <jgg@ziepe.ca>
To: Ralph Campbell <rcampbell@nvidia.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
	nouveau@lists.freedesktop.org,
	"Jérôme Glisse" <jglisse@redhat.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Christoph Hellwig" <hch@lst.de>
Subject: Re: [PATCH 2/2] mm/hmm: hmm_range_fault() infinite loop
Date: Tue, 27 Aug 2019 19:22:19 -0300	[thread overview]
Message-ID: <20190827222219.GA30700@ziepe.ca> (raw)
In-Reply-To: <f5c1f198-4bdd-3c23-428f-764f894b9997@nvidia.com>

On Tue, Aug 27, 2019 at 01:16:13PM -0700, Ralph Campbell wrote:
> 
> On 8/27/19 11:41 AM, Jason Gunthorpe wrote:
> > On Fri, Aug 23, 2019 at 03:17:53PM -0700, Ralph Campbell wrote:
> > 
> > > Signed-off-by: Ralph Campbell <rcampbell@nvidia.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
> > 
> walk->vma can be NULL. hmm_vma_do_fault() no longer touches it
> unconditionally, that is what the preceding patch fixes.
> I suppose I could change hmm_vma_walk_hole_() to check for NULL
> and fill in the pfns[] array, I just chose to handle it in
> hmm_vma_do_fault().

Okay, yes maybe long term it would be clearer to do the vma null check
closer to the start of the callback, but this is a good enough bug fix

Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>

Jason