netdev - Re: [PATCH 3/4] bonding: Deadlock between bonding_store_bonds and bond_destroy

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Date:	Fri, 02 May 2008 17:51:53 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	fubar@...ibm.com
Cc:	netdev@...r.kernel.org, jgarzik@...ox.com, xemul@...nvz.org
Subject: Re: [PATCH 3/4] bonding: Deadlock between bonding_store_bonds and
 bond_destroy_sysfs.

From: Jay Vosburgh <fubar@...ibm.com>
Date: Fri,  2 May 2008 17:49:39 -0700

> From: Pavel Emelyanov <xemul@...nvz.org>
> 
> The sysfs layer has an internal protection, that ensures, that
> all the process sitting inside ->sore/->show callback exits
> before the appropriate entry is unregistered (the calltraces
> are rather big, but I can provide them if required).
> 
> On the other hand, bonding takes rtnl_lock in
> a) the bonding_store_bonds, i.e. in ->store callback,
> b) module exit before calling the sysfs unregister routines.
> 
> Thus, the classical AB-BA deadlock may occur. To reproduce run
> # while :; do modprobe bonding; rmmod bonding; done
> and
> # while :; do echo '+bond%d' > /sys/class/net/bonding_masters ; done
> in parallel.
> 
> The fix is to move the bond_destroy_sysfs out of the rtnl_lock,
> but _before_ bond_free_all to make sure no bonding devices exist
> after module unload.
> 
> Signed-off-by: Pavel Emelyanov <xemul@...nvz.org>
> Acked-by: Jay Vosburgh <fubar@...ibm.com>

Acked-by: David S. Miller <davem@...emloft.net>
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