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From: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
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>
Subject: Re: xen/p2m: m2p_find_override: use list_for_each_entry_safe
Date: Fri, 20 Apr 2012 12:23:21 +0100	[thread overview]
Message-ID: <alpine.DEB.2.00.1204201213100.26786@kaball-desktop> (raw)
In-Reply-To: <20120420105112.GA21487@elgon.mountain>

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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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  reply	other threads:[~2012-04-20 11:23 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-04-20 10:51 xen/p2m: m2p_find_override: use list_for_each_entry_safe Dan Carpenter
2012-04-20 11:23 ` Stefano Stabellini [this message]
2012-04-20 11:35   ` Dan Carpenter
2012-04-20 13:36     ` Stefano Stabellini
2012-04-20 16:01       ` Konrad Rzeszutek Wilk

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