netdev - Re: [PATCH net v2] openvswitch: fix a possible deadlock and lockdep warning

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Message-ID: <CAEP_g=--TMq8s4JdSTcybXgGM6o8mqrWh1NWGFt2Jy4QQuXjmA@mail.gmail.com>
Date:	Thu, 27 Mar 2014 10:37:32 -0700
From:	Jesse Gross <jesse@...ira.com>
To:	Pravin Shelar <pshelar@...ira.com>, Jesse Gross <jesse@...ira.com>,
	netdev <netdev@...r.kernel.org>,
	openvswitch <dev@...nvswitch.org>
Subject: Re: [PATCH net v2] openvswitch: fix a possible deadlock and lockdep warning

On Thu, Mar 27, 2014 at 10:33 AM, Flavio Leitner <fbl@...hat.com> wrote:
> On Thu, Mar 27, 2014 at 10:19:23AM -0700, Pravin Shelar wrote:
>> On Thu, Mar 27, 2014 at 7:05 AM, Flavio Leitner <fbl@...hat.com> wrote:
>> > There are two problematic situations.
>> >
>> > A deadlock can happen when is_percpu is false because it can get
>> > interrupted while holding the spinlock. Then it executes
>> > ovs_flow_stats_update() in softirq context which tries to get
>> > the same lock.
>> >
>> > The second sitation is that when is_percpu is true, the code
>> > correctly disables BH but only for the local CPU, so the
>> > following can happen when locking the remote CPU without
>> > disabling BH:
>> >
>> >        CPU#0                            CPU#1
>> >   ovs_flow_stats_get()
>> >    stats_read()
>> >  +->spin_lock remote CPU#1        ovs_flow_stats_get()
>> >  |  <interrupted>                  stats_read()
>> >  |  ...                       +-->  spin_lock remote CPU#0
>> >  |                            |     <interrupted>
>> >  |  ovs_flow_stats_update()   |     ...
>> >  |   spin_lock local CPU#0 <--+     ovs_flow_stats_update()
>> >  +---------------------------------- spin_lock local CPU#1
>> >
>> > This patch disables BH for both cases fixing the deadlocks.
>>
>> This bug is already fixed in OVS.
>
> Could you point me to the commit? I am not finding anything
> recent.

This is the commit:

commit 9d73c9cac76ba557fdac4a89c1b7eafe132b85a3
Author: Pravin B Shelar <pshelar@...ira.com>
Date:   Tue Dec 17 15:43:30 2013 -0800

    datapath: Fix deadlock during stats update.

I thought that I had sent it in the most recent batch of changes for
net but it looks like I missed it.
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