netdev - Re: [PATCH net-next v3] bonding: fix system hang due to fast igmp timer rescheduling

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Message-Id: <20130801.155311.357862923906678467.davem@davemloft.net>
Date:	Thu, 01 Aug 2013 15:53:11 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	nikolay@...hat.com
Cc:	netdev@...r.kernel.org, andy@...yhouse.net, fubar@...ibm.com
Subject: Re: [PATCH net-next v3] bonding: fix system hang due to fast igmp
 timer rescheduling

From: Nikolay Aleksandrov <nikolay@...hat.com>
Date: Thu,  1 Aug 2013 11:51:42 +0200

> From: "Nikolay Aleksandrov" <nikolay@...hat.com>
> 
> After commit 4aa5dee4d9 ("net: convert resend IGMP to notifier event")
> we try to acquire rtnl in bond_resend_igmp_join_requests but it can be
> scheduled with rtnl already held (e.g. when bond_change_active_slave is
> called with rtnl) causing a loop of immediate reschedules + calls because
> rtnl_trylock fails each time since it's being already held.
> For me this issue leads to system hangs very easy:
> modprobe bonding; ifconfig bond0 up; ifenslave bond0 eth0; rmmod
> bonding;
> 
> The fix is to introduce a small (1 jiffy) delay which is enough for the
> sections holding rtnl to finish without putting any strain on the system.
> Also adjust the timer in bond_change_active_slave to be 1 jiffy, since
> most of the time it's called with rtnl already held.
> 
> Signed-off-by: Nikolay Aleksandrov <nikolay@...hat.com>

Applied, thanks.
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