netdev - Re: [PATCH] cxgb4: disable BH when hold the adap_rcu

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Message-ID: <1403186089.1225.12.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Thu, 19 Jun 2014 06:54:49 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	roy.qing.li@...il.com
Cc:	netdev@...r.kernel.org, greearb@...delatech.com,
	leedom@...lsio.com, hariprasad@...lsio.com
Subject: Re: [PATCH] cxgb4: disable BH when hold the adap_rcu_lock lock

On Thu, 2014-06-19 at 06:40 -0700, Eric Dumazet wrote:
> On Thu, 2014-06-19 at 17:06 +0800, roy.qing.li@...il.com wrote:
> > From: Li RongQing <roy.qing.li@...il.com>
> > 
> > This lock is used in BH enabled condition and softirq context, so need to
> > disable BH to avoid the dead lock:
> > 	=================================
> > 	[ INFO: inconsistent lock state ]
> > 	3.14.7+ #24 Tainted: G         C O
> > 	---------------------------------
> > 	inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
> > 	radvd/3794 [HC0[0]:SC1[1]:HE1:SE0] takes:
> > 	 (adap_rcu_lock){+.?...}, at: [<ffffffffa09989ea>] clip_add+0x2c/0x116 [cxgb4]
> > 	{SOFTIRQ-ON-W} state was registered at:
> > 	  [<ffffffff810fca81>] __lock_acquire+0x34a/0xe48
> > 	  [<ffffffff810fd98b>] lock_acquire+0x82/0x9d
> > 	  [<ffffffff815d6ff8>] _raw_spin_lock+0x34/0x43
> > 	  [<ffffffffa09989ea>] clip_add+0x2c/0x116 [cxgb4]
> > 	  [<ffffffffa0998beb>] cxgb4_inet6addr_handler+0x117/0x12c [cxgb4]
> > 	  [<ffffffff815da98b>] notifier_call_chain+0x32/0x5c
> > 	  [<ffffffff815da9f9>] __atomic_notifier_call_chain+0x44/0x6e
> > 	  [<ffffffff815daa32>] atomic_notifier_call_chain+0xf/0x11
> > 	  [<ffffffff815b1356>] inet6addr_notifier_call_chain+0x16/0x18
> > 	  [<ffffffffa01f72e5>] ipv6_add_addr+0x404/0x46e [ipv6]
> > 	  [<ffffffffa01f8df0>] addrconf_add_linklocal+0x5f/0x95 [ipv6]
> > 	  [<ffffffffa01fc3e9>] addrconf_notify+0x632/0x841 [ipv6]
> > 	  [<ffffffff815da98b>] notifier_call_chain+0x32/0x5c
> > 	  [<ffffffff810e09a1>] __raw_notifier_call_chain+0x9/0xb
> > 	  [<ffffffff810e09b2>] raw_notifier_call_chain+0xf/0x11
> > 	  [<ffffffff8151b3b7>] call_netdevice_notifiers_info+0x4e/0x56
> > 	  [<ffffffff8151b3d0>] call_netdevice_notifiers+0x11/0x13
> > 	  [<ffffffff8151c0a6>] netdev_state_change+0x1f/0x38
> > 	  [<ffffffff8152f004>] linkwatch_do_dev+0x3b/0x49
> > 	  [<ffffffff8152f184>] __linkwatch_run_queue+0x10b/0x144
> > 	  [<ffffffff8152f1dd>] linkwatch_event+0x20/0x27
> > 	  [<ffffffff810d7bc0>] process_one_work+0x1cb/0x2ee
> > 	  [<ffffffff810d7e3b>] worker_thread+0x12e/0x1fc
> > 	  [<ffffffff810dd391>] kthread+0xc4/0xcc
> > 	  [<ffffffff815dc48c>] ret_from_fork+0x7c/0xb0
> > 	irq event stamp: 3388
> > 	hardirqs last  enabled at (3388): [<ffffffff810c6c85>] __local_bh_enable_ip+0xaa/0xd9
> > 	hardirqs last disabled at (3387): [<ffffffff810c6c2d>] __local_bh_enable_ip+0x52/0xd9
> > 	softirqs last  enabled at (3288): [<ffffffffa01f1d5b>] rcu_read_unlock_bh+0x0/0x2f [ipv6]
> > 	softirqs last disabled at (3289): [<ffffffff815ddafc>] do_softirq_own_stack+0x1c/0x30
> > 
> > 	other info that might help us debug this:
> > 	 Possible unsafe locking scenario:
> > 
> > 	       CPU0
> > 	       ----
> > 	  lock(adap_rcu_lock);
> > 	  <Interrupt>
> > 	    lock(adap_rcu_lock);
> > 
> > 	 *** DEADLOCK ***
> 
> Sorry, I do not understand the problem.
> 
> This lock should be taken from process context only.
> 
> You did not provide full lockdep report, did you ?

Right, appropriate fix is really :

diff --git a/drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c b/drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c
index 2f8d6b910383..93d5287544ab 100644
--- a/drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c
+++ b/drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c
@@ -4057,22 +4057,19 @@ int cxgb4_unregister_uld(enum cxgb4_uld type)
 EXPORT_SYMBOL(cxgb4_unregister_uld);
 
 /* Check if netdev on which event is occured belongs to us or not. Return
- * suceess (1) if it belongs otherwise failure (0).
+ * success (true) if it belongs otherwise failure (false).
+ * Called with rcu_read_lock() held.
  */
-static int cxgb4_netdev(struct net_device *netdev)
+static bool cxgb4_netdev(const struct net_device *netdev)
 {
 	struct adapter *adap;
 	int i;
 
-	spin_lock(&adap_rcu_lock);
 	list_for_each_entry_rcu(adap, &adap_rcu_list, rcu_node)
 		for (i = 0; i < MAX_NPORTS; i++)
-			if (adap->port[i] == netdev) {
-				spin_unlock(&adap_rcu_lock);
-				return 1;
-			}
-	spin_unlock(&adap_rcu_lock);
-	return 0;
+			if (adap->port[i] == netdev)
+				return true;
+	return false;
 }
 
 static int clip_add(struct net_device *event_dev, struct inet6_ifaddr *ifa,


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