linux-kernel - Re: LTP regressions due to 6dc296e7df4c ("mm: make sure all file VMAs have ->vm

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Date:	Mon, 14 Sep 2015 19:46:09 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:	Will Deacon <will.deacon@....com>, hpa@...or.com,
	luto@...capital.net, dave.hansen@...ux.intel.com, mingo@...e.hu,
	minchan@...nel.org, tglx@...utronix.de, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: LTP regressions due to 6dc296e7df4c ("mm: make sure all file
	VMAs have ->vm_ops set")

On 09/14, Oleg Nesterov wrote:
>
> On 09/14, Kirill A. Shutemov wrote:
> >
> > Fix is below. I don't really like it, but I cannot find any better
> > solution.
>
> Me too...
>
> But this change "documents" the nasty special "vm_file && !vm_ops" case, and
> I am not sure how we can remove it later...
>
> So perhaps we should change vma_is_anonymous() back to check ->fault too,
>
> 	 static inline bool vma_is_anonymous(struct vm_area_struct *vma)
> 	 {
> 	-	return !vma->vm_ops;
> 	+	return !vma->vm_ops || !vma->vm_ops->fault;
> 	 }
>
> and remove the "vma->vm_file && !vma->vm_ops" checks in mmap_region() paths.
  ^^^

sorry, I actually meant "or remove". But perhaps "and" makes sense too.

Say, if we change vma_is_anonymous() as above, then we can kill
arch_vma_name() on x86. mpx_mmap() can install the dummy vm_ops with
the single ->name() method.

> I dunno.

Yes. Up to you.

Oleg.

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