netdev - Re: [PATCH net-next] bonding: Fix RTNL: assertion failed at net/core/rtnetlink.c for 802.3ad mode

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Date:	Tue, 18 Feb 2014 12:49:24 +0100
From:	Nikolay Aleksandrov <nikolay@...hat.com>
To:	Ding Tianhong <dingtianhong@...wei.com>,
	Jay Vosburgh <fubar@...ibm.com>,
	Andy Gospodarek <andy@...yhouse.net>,
	Veaceslav Falico <vfalico@...hat.com>,
	Cong Wang <cwang@...pensource.com>,
	Thomas Glanzmann <thomas@...nzmann.de>,
	Jiri Pirko <jiri@...nulli.us>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Scott Feldman <sfeldma@...ulusnetworks.com>,
	Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] bonding: Fix RTNL: assertion failed at net/core/rtnetlink.c
 for 802.3ad mode

On 02/18/2014 12:25 PM, Ding Tianhong wrote:
> The problem was introduced by the commit 1d3ee88ae0d
> (bonding: add netlink attributes to slave link dev).
> The bond_set_active_slave() and bond_set_backup_slave()
> will use rtmsg_ifinfo to send slave's states, so these
> two functions should be called in RTNL.
> 
> In 802.3ad mode, acquiring RTNL for the __enable_port and
> __disable_port cases is difficult, as those calls generally
> already hold the state machine lock, and cannot unconditionally
> call rtnl_lock because either they already hold RTNL (for calls
> via bond_3ad_unbind_slave) or due to the potential for deadlock
> with bond_3ad_adapter_speed_changed, bond_3ad_adapter_duplex_changed,
> bond_3ad_link_change, or bond_3ad_update_lacp_rate.  All four of
> those are called with RTNL held, and acquire the state machine lock
> second.  The calling contexts for __enable_port and __disable_port
> already hold the state machine lock, and may or may not need RTNL.
> 
> According to the Jay's opinion, I don't think it is a problem that
> the slave don't send notify message synchronously when the status
> changed, normally the state machine is running every 100 ms, send
> the notify message at the end of the state machine if the slave's
> state changed should be better.
> 
> I fix the problem through these steps:
> 
> 1). add a new function bond_set_slave_state() which could change
>     the slave's state and call rtmsg_ifinfo() according to the input
>     parameters called notify.
> 
> 2). Add a new slave parameter which called should_notify, if the slave's state
>     changed and don't notify yet, the parameter will be set to 1, and then if
>     the slave's state changed again, the param will be set to 0, it indicate that
>     the slave's state has been restored, no need to notify any one.
> 
> 3). the __enable_port and __disable_port should not call rtmsg_ifinfo
>     in the state machine lock, any change in the state of slave could
>     set a flag in the slave, it will indicated that an rtmsg_ifinfo
>     should be called at the end of the state machine.
> 
> Cc: Jay Vosburgh <fubar@...ibm.com>
> Cc: Veaceslav Falico <vfalico@...hat.com>
> Cc: Andy Gospodarek <andy@...yhouse.net>
> Signed-off-by: Ding Tianhong <dingtianhong@...wei.com>
> ---
Hi Ding,
I think there's a possible race condition which could lead to inconsistent
state because you set slave->should_notify to 0 under RTNL but
__disable_port can update it without RTNL e.g. can be called via
bond_3ad_state_machine_handler -> ad_agg_selection_logic so in theory (I
haven't tested it) they can execute concurrently. This is not a big deal
though, but it would make this kind of message unreliable.

Nik

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