From 2bd9af046fdc10703b266b0f3b25423f0b7d703e Mon Sep 17 00:00:00 2001 From: Xiaotian Feng Date: Wed, 21 Oct 2009 23:07:04 +0000 Subject: [PATCH] isdn: fix possible circular locking dependency MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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: [] isdn_net_device_busy+0x2c/0x74 [isdn]  but task is already holding lock:  (&netdev->local->xmit_lock){+.....}, at: [] 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 Signed-off-by: Xiaotian Feng Signed-off-by: David S. Miller --- drivers/isdn/i4l/isdn_net.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/drivers/isdn/i4l/isdn_net.h b/drivers/isdn/i4l/isdn_net.h index 74032d0881ef..7511f08effa5 100644 --- a/drivers/isdn/i4l/isdn_net.h +++ b/drivers/isdn/i4l/isdn_net.h @@ -83,19 +83,19 @@ static __inline__ isdn_net_local * isdn_net_get_locked_lp(isdn_net_dev *nd) 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;