Message-ID: <4BC2E654.7050002@cn.fujitsu.com>
Date: Mon, 12 Apr 2010 17:22:28 +0800
From: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
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To: Avi Kivity <avi@redhat.com>
CC: Marcelo Tosatti <mtosatti@redhat.com>, KVM list <kvm@vger.kernel.org>,
       LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/6] KVM MMU: fix kvm_mmu_zap_page() and its calling path
References: <4BC2D2E2.1030604@cn.fujitsu.com> <4BC2D345.100@cn.fujitsu.com> <4BC2D8D6.6030306@redhat.com> <4BC2DFA0.6000609@cn.fujitsu.com> <4BC2E2FF.9020005@redhat.com>
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Hi Avi,

Avi Kivity wrote:

> hlist_for_each_entry_safe() is supposed to be be safe against removal of
> the element that is pointed to by the iteration cursor.

If we destroyed the next point, hlist_for_each_entry_safe() is unsafe.

List hlist_for_each_entry_safe()'s code:

|#define hlist_for_each_entry_safe(tpos, pos, n, head, member) 		 \
|	for (pos = (head)->first;					 \
|	     pos && ({ n = pos->next; 1; }) && 				 \
|		({ tpos = hlist_entry(pos, typeof(*tpos), member); 1;}); \
|	     pos = n)

if n is destroyed:
'pos = n, n = pos->next'
then it access n again, it's unsafe/illegal for us.

Xiao
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