Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Jon Maloy <jon.maloy@ericsson.com>
To:     Chris Packham <Chris.Packham@alliedtelesis.co.nz>,
        Eric Dumazet <eric.dumazet@gmail.com>,
        "ying.xue@windriver.com" <ying.xue@windriver.com>,
        "davem@davemloft.net" <davem@davemloft.net>
CC:     "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "tipc-discussion@lists.sourceforge.net" 
        <tipc-discussion@lists.sourceforge.net>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH] tipc: ensure skb->lock is initialised
Thread-Topic: [PATCH] tipc: ensure skb->lock is initialised
Thread-Index: AQHVNRbZCg2+IkEFUEKEsAEksjW2W6bFYzhw
Date:   Thu, 11 Jul 2019 12:55:12 +0000
Message-ID: <CH2PR15MB357528CF6DC0A587D2CB90689AF30@CH2PR15MB3575.namprd15.prod.outlook.com>
References: <MN2PR15MB3581E1D6D56D6AA7DE8E357E9AF00@MN2PR15MB3581.namprd15.prod.outlook.com>
 <4d2ac0ce7f974184ac43b71f19aee7a3@svr-chch-ex1.atlnz.lc>
In-Reply-To: <4d2ac0ce7f974184ac43b71f19aee7a3@svr-chch-ex1.atlnz.lc>
Accept-Language: en-US
Content-Language: en-US
received-spf: None (protection.outlook.com: ericsson.com does not designate
 permitted sender hosts)
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
X-MS-Exchange-CrossTenant-Network-Message-Id: 5edbd025-63ac-427e-1034-08d705ff0341
X-MS-Exchange-CrossTenant-originalarrivaltime: 11 Jul 2019 12:55:12.4390
 (UTC)
X-MS-Exchange-CrossTenant-fromentityheader: Hosted
X-MS-Exchange-CrossTenant-id: 92e84ceb-fbfd-47ab-be52-080c6b87953f
X-MS-Exchange-CrossTenant-mailboxtype: HOSTED
X-MS-Exchange-CrossTenant-userprincipalname: jon.maloy@ericsson.com
X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH2PR15MB3541
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


> -----Original Message-----
> From: Chris Packham <Chris.Packham@alliedtelesis.co.nz>
> Sent: 10-Jul-19 16:58
> To: Jon Maloy <jon.maloy@ericsson.com>; Eric Dumazet
> <eric.dumazet@gmail.com>; ying.xue@windriver.com;
> davem@davemloft.net
> Cc: netdev@vger.kernel.org; tipc-discussion@lists.sourceforge.net; linux-
> kernel@vger.kernel.org
> Subject: Re: [PATCH] tipc: ensure skb->lock is initialised
>=20
>=20
> On 11/07/19 1:10 AM, Jon Maloy wrote:
> >> -----Original Message-----
> >> From: Eric Dumazet <eric.dumazet@gmail.com>
> >> Sent: 10-Jul-19 04:00
> >> To: Jon Maloy <jon.maloy@ericsson.com>; Eric Dumazet
> >> <eric.dumazet@gmail.com>; Chris Packham
> >> <Chris.Packham@alliedtelesis.co.nz>; ying.xue@windriver.com;
> >> davem@davemloft.net
> >> Cc: netdev@vger.kernel.org; tipc-discussion@lists.sourceforge.net;
> >> linux- kernel@vger.kernel.org
> >> Subject: Re: [PATCH] tipc: ensure skb->lock is initialised
> >>
> >>
> >>
> >> On 7/9/19 10:15 PM, Jon Maloy wrote:
> >>>
> >>> It is not only for lockdep purposes, -it is essential.  But please
> >>> provide details
> >> about where you see that more fixes are needed.
> >>>
> >>
> >> Simple fact that you detect a problem only when skb_queue_purge() is
> >> called should talk by itself.
> >>
> >> As I stated, there are many places where the list is manipulated
> >> _without_ its spinlock being held.
> >
> > Yes, and that is the way it should be on the send path.
> >
> >>
> >> You want consistency, then
> >>
> >> - grab the spinlock all the time.
> >> - Or do not ever use it.
> >
> > That is exactly what we are doing.
> > - The send path doesn't need the spinlock, and never grabs it.
> > - The receive path does need it, and always grabs it.
> >
> > However, since we don't know from the beginning which path a created
> > message will follow, we initialize the queue spinlock "just in case"
> > when it is created, even though it may never be used later.
> > You can see this as a violation of the principle you are stating
> > above, but it is a prize that is worth paying, given savings in code
> > volume, complexity and performance.
> >
> >>
> >> Do not initialize the spinlock just in case a path will use
> >> skb_queue_purge() (instead of using __skb_queue_purge())
> >
> > I am ok with that. I think we can agree that Chris goes for that
> > solution, so we can get this bug fixed.
>=20
> So would you like a v2 with an improved commit message? I note that I sai=
d
> skb->lock instead of head->lock in the subject line so at least that shou=
ld be
> corrected.

Yes, unless Eric has any more objections.=20
I addition, I have realized that we can change from skb_queue_head_init()  =
to __skb_queue_head_init() at all the disputed locations in the socket code=
.
Then, we do a separate call to spin_lock_init(&list->lock) at the moment we=
 find that the message will follow the receive path, i.e., in tipc_node_xmi=
t().
That should make everybody happy.=20
I will post a patch when net-next re-opens.

BR
///jon