linux-kernel - Re: [PATCH v6 3/5] vmcore: Introduce remap_oldmem_pfn

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Date:	Mon, 15 Jul 2013 10:20:59 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
Cc:	Michael Holzheu <holzheu@...ux.vnet.ibm.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	kexec@...ts.infradead.org,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Jan Willeke <willeke@...ibm.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 3/5] vmcore: Introduce remap_oldmem_pfn_range()

On Fri, Jul 12, 2013 at 08:05:31PM +0900, HATAYAMA Daisuke wrote:

[..]
> How about
> 
> static int mmap_vmcore_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
> {
> ...
>         char *buf;
>         int rc;
> 
> #ifndef CONFIG_S390
>         return VM_FAULT_SIGBUS;
> #endif
>         page = find_or_create_page(mapping, index, GFP_KERNEL);
> 
> Considering again, I don't think WARN_ONCE() is good now. The fact that fault occurs on
> mmap() region indicates some kind of buggy situation occurs on the process. The process
> should be killed as soon as possible. If user still wants to get crash dump, he should
> try again in another process.

I don't understand that. Process should be killed only if there was no
mapping created for the region process is trying to access.

If there is a mapping but we are trying to fault in the actual contents,
then it is not a problem of process. Process is accessing a region of 
memory which it is supposed to access.

Potential problem here is that remap_pfn_range() did not map everything
it was expected to so we have to resort on page fault handler to read
that in. So it is more of a kernel issue and not process issue and for
that WARN_ONCE() sounds better?

Vivek
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