isdn: fix possible circular locking dependency
There's a circular locking dependency:
---> isdn_net_get_locked_lp
--->lock &nd->queue_lock
--->lock &nd->queue->xmit_lock
.....................
---->unlock &nd->queue_lock
---> isdn_net_writebuf_skb (called with &nd->queue->xmit_lock locked)
---->isdn_net_inc_frame_cnt
---->isdn_net_device_busy
----> lock &nd->queue_lock
This will trigger lockdep warnings:
=======================================================
[ INFO: possible circular locking dependency detected ]
2.6.32-rc4-testing #7
-------------------------------------------------------
ipppd/28379 is trying to acquire lock:
(&netdev->queue_lock){......}, at: [<e62ad0fd>] isdn_net_device_busy+0x2c/0x74 [isdn]
but task is already holding lock:
(&netdev->local->xmit_lock){+.....}, at: [<e62aefc2>] isdn_net_write_super+0x3f/0x6e [isdn]
which lock already depends on the new lock.
.......
We don't need to lock nd->queue->xmit_lock to protect single
isdn_net_lp_busy(). This can fix above lockdep warnings.
Reported-and-tested-by: Tilman Schmidt <tilman@imap.cc>
Signed-off-by: Xiaotian Feng <xtfeng@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/isdn/i4l/isdn_net.h b/drivers/isdn/i4l/isdn_net.h
index 74032d0..7511f08 100644
--- a/drivers/isdn/i4l/isdn_net.h
+++ b/drivers/isdn/i4l/isdn_net.h
@@ -83,19 +83,19 @@
spin_lock_irqsave(&nd->queue_lock, flags);
lp = nd->queue; /* get lp on top of queue */
- spin_lock(&nd->queue->xmit_lock);
while (isdn_net_lp_busy(nd->queue)) {
- spin_unlock(&nd->queue->xmit_lock);
nd->queue = nd->queue->next;
if (nd->queue == lp) { /* not found -- should never happen */
lp = NULL;
goto errout;
}
- spin_lock(&nd->queue->xmit_lock);
}
lp = nd->queue;
nd->queue = nd->queue->next;
+ spin_unlock_irqrestore(&nd->queue_lock, flags);
+ spin_lock(&lp->xmit_lock);
local_bh_disable();
+ return lp;
errout:
spin_unlock_irqrestore(&nd->queue_lock, flags);
return lp;