From mboxrd@z Thu Jan  1 00:00:00 1970
From: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Subject: Re: xen/p2m: m2p_find_override: use
	list_for_each_entry_safe
Date: Fri, 20 Apr 2012 12:23:21 +0100
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References: <20120420105112.GA21487@elgon.mountain>
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To: Dan Carpenter <dan.carpenter@oracle.com>
Cc: "xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>, Stefano Stabellini <Stefano.Stabellini@eu.citrix.com>
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On Fri, 20 Apr 2012, Dan Carpenter wrote:
> Hi Stefano,
> 
> I had a question about 8f2854c74ff4: "xen/p2m: m2p_find_override: use
> list_for_each_entry_safe".
> 
> I think there is a misunderstanding about what the
> list_for_each_entry_safe() macro does.  It has nothing to do with
> locking, so the spinlock is still needed.  Without the lock ->next could
> point to an element which has been deleted in another thread.  Probably
> the patch should be reverted.

I thought that list_for_each_entry_safe is safe against deletion, is it
not?
It doesn't matter whether we get up to date entries or old entries
here as long as walking through the list doesn't break if a concurrent
thread adds or removes items.


> Also, it introduces a GCC warning:
> arch/x86/xen/p2m.c:811:16: warning: unused variable ‘flags’
> 	[-Wunused-variable]

I think that Konrad didn't submit the latest version of the patch (v3),
that has a better description and also removes the flags variable:
http://marc.info/?l=linux-kernel&m=133407526406072&w=2
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