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

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Date:	Fri,  2 May 2008 17:49:39 -0700
From:	Jay Vosburgh <fubar@...ibm.com>
To:	netdev@...r.kernel.org
Cc:	Jeff Garzik <jgarzik@...ox.com>, Pavel Emelyanov <xemul@...nvz.org>
Subject: [PATCH 3/4] bonding: Deadlock between bonding_store_bonds and bond_destroy_sysfs.

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>
---
 drivers/net/bonding/bond_main.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index 7ffd819..3977760 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -4995,9 +4995,10 @@ err:
 		destroy_workqueue(bond->wq);
 	}

+	bond_destroy_sysfs();
+
 	rtnl_lock();
 	bond_free_all();
-	bond_destroy_sysfs();
 	rtnl_unlock();
 out:
 	return res;
@@ -5009,9 +5010,10 @@ static void __exit bonding_exit(void)
 	unregister_netdevice_notifier(&bond_netdev_notifier);
 	unregister_inetaddr_notifier(&bond_inetaddr_notifier);

+	bond_destroy_sysfs();
+
 	rtnl_lock();
 	bond_free_all();
-	bond_destroy_sysfs();
 	rtnl_unlock();
 }

-- 
1.5.2.4

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