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Date:   Thu, 8 Feb 2018 10:18:00 -0800
From:   Matthew Wilcox <willy@infradead.org>
To:     Laura Abbott <labbott@redhat.com>
Cc:     Kai Heng Feng <kai.heng.feng@canonical.com>,
        Michal Hocko <mhocko@suse.com>, linux-mm@kvack.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: Regression after commit 19809c2da28a ("mm, vmalloc: use
 __GFP_HIGHMEM implicitly")
Message-ID: <20180208181800.GA9524@bombadil.infradead.org>
References: <627DA40A-D0F6-41C1-BB5A-55830FBC9800@canonical.com>
 <20180208130649.GA15846@bombadil.infradead.org>
 <f8be3fc9-a96d-bf37-4da0-43220014caed@redhat.com>
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On Thu, Feb 08, 2018 at 09:56:42AM -0800, Laura Abbott wrote:
> > +++ b/drivers/media/v4l2-core/videobuf-dma-sg.c
> > @@ -77,7 +77,7 @@ static struct scatterlist *videobuf_vmalloc_to_sg(unsigned char *virt,
> >   		pg = vmalloc_to_page(virt);
> >   		if (NULL == pg)
> >   			goto err;
> > -		BUG_ON(PageHighMem(pg));
> > +		BUG_ON(page_to_pfn(pg) >= (1 << (32 - PAGE_SHIFT)));
> >   		sg_set_page(&sglist[i], pg, PAGE_SIZE, 0);
> >   	}
> >   	return sglist;
> > 
> 
> the vzalloc in this function needs to be switched to vmalloc32 if it
> actually wants to guarantee 32-bit memory.

Whoops, you got confused between the sglist allocation and the allocation
of the pages which will be mapped ...