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

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Message-ID: <CALnjE+q41G9KKf_EhTdDvZtX_Xao_WG+KhRZ2fKe0JF8sqjZxw@mail.gmail.com>
Date:	Thu, 27 Mar 2014 10:19:23 -0700
From:	Pravin Shelar <pshelar@...ira.com>
To:	Flavio Leitner <fbl@...hat.com>, Jesse Gross <jesse@...ira.com>
Cc:	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 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.

Jesse,
Can you send the fix upstream or you waiting for other patches?
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