netpoll: convert mutex into a semaphore (bd7c4b60) · Commits · 戴 / test

Bart Van Assche recently reported a warning to me: <IRQ> [<ffffffff8103d79f>] warn_slowpath_common+0x7f/0xc0 [<ffffffff8103d7fa>] warn_slowpath_null+0x1a/0x20 [<ffffffff814761dd>] mutex_trylock+0x16d/0x180 [<ffffffff813968c9>] netpoll_poll_dev+0x49/0xc30 [<ffffffff8136a2d2>] ? __alloc_skb+0x82/0x2a0 [<ffffffff81397715>] netpoll_send_skb_on_dev+0x265/0x410 [<ffffffff81397c5a>] netpoll_send_udp+0x28a/0x3a0 [<ffffffffa0541843>] ? write_msg+0x53/0x110 [netconsole] [<ffffffffa05418bf>] write_msg+0xcf/0x110 [netconsole] [<ffffffff8103eba1>] call_console_drivers.constprop.17+0xa1/0x1c0 [<ffffffff8103fb76>] console_unlock+0x2d6/0x450 [<ffffffff8104011e>] vprintk_emit+0x1ee/0x510 [<ffffffff8146f9f6>] printk+0x4d/0x4f [<ffffffffa0004f1d>] scsi_print_command+0x7d/0xe0 [scsi_mod] This resulted from my commit which introduced a mutex_trylock operation in a path that could execute in interrupt context. When mutex debugging is enabled, the above warns the user when we are in fact exectuting in interrupt context interrupt context. After some discussion, It seems that a semaphore is the proper mechanism to use here. While mutexes are defined to be unusable in interrupt context, no such condition exists for semaphores (save for the fact that the non blocking api calls, like up and down_trylock must be used when in irq context). Signed-off-by:

Neil Horman <nhorman@tuxdriver.com> Reported-by:

Bart Van Assche <bvanassche@acm.org> CC: Bart Van Assche <bvanassche@acm.org> CC: David Miller <davem@davemloft.net> CC: netdev@vger.kernel.org Signed-off-by:

David S. Miller <davem@davemloft.net>

include/linux/netpoll.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -40,7 +40,7 @@ struct netpoll_info {

		unsigned long rx_flags;
		spinlock_t rx_lock;
		struct mutex dev_lock;
		struct semaphore dev_lock;
		struct list_head rx_np; /* netpolls that registered an rx_hook */

		struct sk_buff_head neigh_tx; /* list of neigh requests to reply to */

net/core/netpoll.c

+7 −7

Original line number	Diff line number	Diff line
		@@ -206,17 +206,17 @@ static void netpoll_poll_dev(struct net_device *dev)
		* the dev_open/close paths use this to block netpoll activity
		* while changing device state
		*/
		if (!mutex_trylock(&ni->dev_lock))
		if (!down_trylock(&ni->dev_lock))
		return;

		if (!netif_running(dev)) {
		mutex_unlock(&ni->dev_lock);
		up(&ni->dev_lock);
		return;
		}

		ops = dev->netdev_ops;
		if (!ops->ndo_poll_controller) {
		mutex_unlock(&ni->dev_lock);
		up(&ni->dev_lock);
		return;
		}

		@@ -225,7 +225,7 @@ static void netpoll_poll_dev(struct net_device *dev)

		poll_napi(dev);

		mutex_unlock(&ni->dev_lock);
		up(&ni->dev_lock);

		if (dev->flags & IFF_SLAVE) {
		if (ni) {
		@@ -255,7 +255,7 @@ int netpoll_rx_disable(struct net_device *dev)
		idx = srcu_read_lock(&netpoll_srcu);
		ni = srcu_dereference(dev->npinfo, &netpoll_srcu);
		if (ni)
		mutex_lock(&ni->dev_lock);
		down(&ni->dev_lock);
		srcu_read_unlock(&netpoll_srcu, idx);
		return 0;
		}
		@@ -267,7 +267,7 @@ void netpoll_rx_enable(struct net_device *dev)
		rcu_read_lock();
		ni = rcu_dereference(dev->npinfo);
		if (ni)
		mutex_unlock(&ni->dev_lock);
		up(&ni->dev_lock);
		rcu_read_unlock();
		}
		EXPORT_SYMBOL(netpoll_rx_enable);
		@@ -1047,7 +1047,7 @@ int __netpoll_setup(struct netpoll np, struct net_device ndev, gfp_t gfp)
		INIT_LIST_HEAD(&npinfo->rx_np);

		spin_lock_init(&npinfo->rx_lock);
		mutex_init(&npinfo->dev_lock);
		sema_init(&npinfo->dev_lock, 1);
		skb_queue_head_init(&npinfo->neigh_tx);
		skb_queue_head_init(&npinfo->txq);
		INIT_DELAYED_WORK(&npinfo->tx_work, queue_process);

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