Re: [Xen-devel] cpupools and locking

To:	George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Keir Fraser <Keir.Fraser@xxxxxxxxxxxxx>
Subject:	Re: [Xen-devel] cpupools and locking
From:	Juergen Gross <juergen.gross@xxxxxxxxxxxxxx>
Date:	Wed, 05 May 2010 07:25:51 +0200
Cc:	xen-devel@xxxxxxxxxxxxxxxxxxx
Delivery-date:	Tue, 04 May 2010 22:26:40 -0700
Dkim-signature:	v=1; a=rsa-sha256; c=simple/simple; d=ts.fujitsu.com; i=juergen.gross@xxxxxxxxxxxxxx; q=dns/txt; s=s1536b; t=1273037087; x=1304573087; h=message-id:date:from:mime-version:to:cc:subject: references:in-reply-to:content-transfer-encoding; z=Message-ID:=20<4BE1015F.8050901@xxxxxxxxxxxxxx>\|Date:=20 Wed,=2005=20May=202010=2007:25:51=20+0200\|From:=20Juergen =20Gross=20<juergen.gross@xxxxxxxxxxxxxx>\|MIME-Version: =201.0\|To:=20George=20Dunlap=20<George.Dunlap@xxxxxxxxxxx om>,=20=0D=0A=20Keir=20Fraser=20<Keir.Fraser@xxxxxxxxxxxx m>\|CC:=20xen-devel@xxxxxxxxxxxxxxxxxxx\|Subject:=20Re:=20[ Xen-devel]=20cpupools=20and=20locking\|References:=20<w2jd e76405a1005041151lded10645z70c2ed600e0728a1@xxxxxxxxxxxxx m>\|In-Reply-To:=20<w2jde76405a1005041151lded10645z70c2ed6 00e0728a1@xxxxxxxxxxxxxx>\|Content-Transfer-Encoding:=207b it; bh=x0pmI0SLQcWfiynrckhzbV9qCwPmAvIxKH33BcFcprc=; b=JC5rhG9xhgrHfLmaVqgQC9ESg71ZpqGohz8OQvaCChsMjptcaSN/dveW Px5vy/jGQI7WW2ukk5SeDVt8QLU+Sjrw/GosVXZPGh02Edgv5pNlrCKEJ 8sXPY8XYkoq+t0bYawH1AiN9ODRpsMHMkhdNAmTFpcJln25MaWQ86drDl 50eL7+jkcRDecStJ8xcZ5QDmICTlwVbPRhJLWieecnr7qwpnCa6Gdxtvm CQgmeKRzYdGBkX+aeqf+vCnLq4nBM;
Domainkey-signature:	s=s1536a; d=ts.fujitsu.com; c=nofws; q=dns; h=X-SBRSScore:X-IronPort-AV:Received:X-IronPort-AV: Received:Received:Message-ID:Date:From:Organization: User-Agent:MIME-Version:To:CC:Subject:References: In-Reply-To:Content-Type:Content-Transfer-Encoding; b=BXfHRvb/6WUEYZpfjIU35dOnfdcJd3F0yIhFsQ2/peu8X08LFeuvG8DJ yKQCN5l+RqDPn8G4uaKNwVr+jsnDV5QgkWK1swBSh/VYFRb4FofYsll04 gyDT/iZPHMHP1hhkvsPkFtM3ZVpgFYEoQJ+HoIhd/OTMjvbXaW1Cl1yzL tdKIZ/Dpjs/9s5scVFqDk+uzEZXhWU6j1lAeeCsbPhVgZ3dwNe7EEwXvj 4hyAYUhvb/GLq7cE8ilw+CBdLtzaR;
Envelope-to:	www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to:	<w2jde76405a1005041151lded10645z70c2ed600e0728a1@xxxxxxxxxxxxxx>
List-help:	<mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id:	Xen developer discussion <xen-devel.lists.xensource.com>
List-post:	<mailto:xen-devel@lists.xensource.com>
List-subscribe:	<http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe:	<http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
Organization:	Fujitsu Technology Solutions
References:	<w2jde76405a1005041151lded10645z70c2ed600e0728a1@xxxxxxxxxxxxxx>
Sender:	xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
User-agent:	Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.9) Gecko/20100411 Iceowl/1.0b1 Icedove/3.0.4

On 05/04/2010 08:51 PM, George Dunlap wrote:

Something seems not quite right about the cpupool locking... in
xen/common/cpupool.c:cpupool_do_domctl(), the cpupool_lock is only
held during the find for several operations.  Doesn't that mean that,
for instance, it's possible for someone to call CPUPOOL_OP_DESTROY,
while someone concurrently calls CPUPOOL_OP_INFO, such that in the
INFO case, the find succeeds, but the structure is shortly thereafter
freed by DESTROY, even though INFO code still has a pointer to it
which may be dereferenced?  I don't see any reference counting... am I
missing something?


cpupool_do_domctl is called always while the domctl lock is being held. Maybe
I should have added a comment to document this assumption.

Keir's patch to move the cpupool commands to the sysctl interface makes a
change of the locking mandatory. I'll setup a patch for this.


Juergen

--
Juergen Gross                 Principal Developer Operating Systems
TSP ES&S SWE OS6                       Telephone: +49 (0) 89 3222 2967
Fujitsu Technology Solutions              e-mail: juergen.gross@xxxxxxxxxxxxxx
Domagkstr. 28                           Internet: ts.fujitsu.com
D-80807 Muenchen                 Company details: ts.fujitsu.com/imprint.html

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel

WARNING - OLD ARCHIVES

xen-devel

Re: [Xen-devel] cpupools and locking