linux-kernel - Re: [PATCH 01/10] cramfs: Convert to use vmf_insert

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Date:   Tue, 28 Aug 2018 15:04:27 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Nicolas Pitre <nicolas.pitre@...aro.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Souptick Joarder <jrdr.linux@...il.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 01/10] cramfs: Convert to use vmf_insert_mixed

On Tue, Aug 28, 2018 at 01:49:25PM -0400, Nicolas Pitre wrote:
> On Tue, 28 Aug 2018, Matthew Wilcox wrote:
> > -			ret = vm_insert_mixed(vma, vma->vm_start + off, pfn);
> > +			vmf = vmf_insert_mixed(vma, vma->vm_start + off, pfn);
> > +			if (vmf & VM_FAULT_ERROR) {
> > +				pages = i;
> > +				break;
> > +			}
> 
> I'd suggest this to properly deal with errers instead:
> 
> -			ret = vm_insert_mixed(vma, vma->vm_start + off, pfn);
> +			vmf = vmf_insert_mixed(vma, vma->vm_start + off, pfn);
> +			if (vmf & VM_FAULT_ERROR)
> +				ret = vm_fault_to_errno(vmf, 0);

By my reading of this function, the intent is actually to return 0
here and allow demand paging to work.  Of course, I've spent all of
twenty minutes staring at this function, so I defer to the maintainer.
I think you'd need to be running a make-memory-allocations-fail fuzzer
to hit this, so it's likely never been tested.