linux-kernel - Re: [patch 5/5] elf: Add support for loading ET

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Date:	Thu, 20 Oct 2011 21:30:44 +0400
From:	Pavel Emelyanov <xemul@...allels.com>
To:	Tejun Heo <tj@...nel.org>
CC:	Cyrill Gorcunov <gorcunov@...nvz.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andrey Vagin <avagin@...allels.com>,
	James Bottomley <jbottomley@...allels.com>,
	Glauber Costa <glommer@...allels.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Daniel Lezcano <dlezcano@...ibm.com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: [patch 5/5] elf: Add support for loading ET_CKPT files

On 10/20/2011 07:56 PM, Tejun Heo wrote:
> Hello,
> 
> On Thu, Oct 20, 2011 at 12:33:51PM +0400, Pavel Emelyanov wrote:
>>> To shared kernel data structures.
>>
>> Yet again - keeping shared stuctres self-consistent from which point of view? From
>> the kernel's one - already handled with in-kernel locks. From the userspace one -
>> every single kernel API provides a *way* to do things right, but doesn't provide
>> the fool protection.
> 
> Sigh, no, in exec and related paths, the fact that all other threads
> have been zapped are depended upon and the exec'ing task assumes
> exclusive access to resources which in usual cases would require other
> forms of exclusion.  Maybe there are not too many of them and things
> can definitely be audited and updated but it is pretty intricate down
> there and I just don't see good enough justification here.

The amount of new kernel API is good justification. I've sent the list of what
should we allow to change from user-space for the sake of restore only.

Anyway - let's wait for Cyrill's work done in this area.

>>> IMHO, this is a fundamentally broken approach which isn't even
>>> necessary.  So, FWIW, NACK.
>>
>> It's a pity :( Anyway, as I stated above, we'll try to compare two
>> real implementations, not abstract assumptions.
> 
> Given the state of this thread, I'm pretty skeptical this one can
> survive but, hey, who knows?

That's good to hear that you're still open for discussion.

> Thank you.

Thanks,
Pavel
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