linux-kernel - Re: [xen] double fault: 0000 [#1] PREEMPT SMP DEBUG

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Date:	Wed, 9 Oct 2013 19:38:53 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Dave Airlie <airlied@...ux.ie>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Fengguang Wu <fengguang.wu@...el.com>,
	xen-devel@...ts.xenproject.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [xen] double fault: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC

On Wed, Oct 9, 2013 at 7:23 PM, Dave Airlie <airlied@...ux.ie> wrote:
>
> Well the commit that added it had a reason that seems to cover some other
> device model abuses, so maybe someone who actually understands the device
> model (all 2 people) can review usage

Actually, I think it's the same bug.

You *cannot* just reuse the storage. Doing a "memset()" doesn't
improve anything. The basic issue is that if you reuse it, you're
buggy. End of story.

Why? It's refcounted, and it's out of your hands. Reusing it is wrong
- because it might still be used. The fact that you "released" it is
immaterial. Others can have refcounts (and through /sys etc,
historically really do have them).

            Linus
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