netdev - [PATCH] cnic: don't take the rtnl_read_lock in cnic_rcv

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Message-Id: <1401462019-7958-1-git-send-email-nhorman@tuxdriver.com>
Date:	Fri, 30 May 2014 11:00:19 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	netdev@...r.kernel.org
Cc:	Neil Horman <nhorman@...driver.com>,
	"David S. Miller" <davem@...emloft.net>,
	Michael Chan <mchan@...adcom.com>, fcoe-devel@...n-fcoe.org,
	Robert Love <robert.w.love@...el.com>,
	Vasu Dev <vasu.dev@...el.com>
Subject: [PATCH] cnic: don't take the rtnl_read_lock in cnic_rcv_netevent

The Cnic driver handles lots of ulp operations in its netdevice event hanlder.
To do this, it accesses the ulp_ops array, which is an rcu protected array.
However, some ulp operations (like bnx2fc_indicate_netevent) try to lock
mutexes, which might sleep (somthing that you can't do while holding rcu read
side locks if you've configured non-preemptive rcu.

Fix this by changing the dereference method.  All accesses to the ulp_ops array
for a cnic dev are modified under the protection of the rtnl lock, and so we can
safely just use rcu_dereference_rtnl, and remove the rcu_read_lock here

Signed-off-by: Neil Horman <nhorman@...driver.com>
CC: "David S. Miller" <davem@...emloft.net>
CC: Michael Chan <mchan@...adcom.com>
CC: fcoe-devel@...n-fcoe.org
CC: Robert Love <robert.w.love@...el.com>
CC: Vasu Dev <vasu.dev@...el.com>
---
 drivers/net/ethernet/broadcom/cnic.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/broadcom/cnic.c b/drivers/net/ethernet/broadcom/cnic.c
index f58a8b8..bfdb9f0 100644
--- a/drivers/net/ethernet/broadcom/cnic.c
+++ b/drivers/net/ethernet/broadcom/cnic.c
@@ -5622,12 +5622,11 @@ static void cnic_rcv_netevent(struct cnic_local *cp, unsigned long event,
 {
 	int if_type;
 
-	rcu_read_lock();
 	for (if_type = 0; if_type < MAX_CNIC_ULP_TYPE; if_type++) {
 		struct cnic_ulp_ops *ulp_ops;
 		void *ctx;
 
-		ulp_ops = rcu_dereference(cp->ulp_ops[if_type]);
+		ulp_ops = rcu_dereference_rtnl(cp->ulp_ops[if_type]);
 		if (!ulp_ops || !ulp_ops->indicate_netevent)
 			continue;
 
@@ -5635,7 +5634,6 @@ static void cnic_rcv_netevent(struct cnic_local *cp, unsigned long event,
 
 		ulp_ops->indicate_netevent(ctx, event, vlan_id);
 	}
-	rcu_read_unlock();
 }
 
 /* netdev event handler */
-- 
1.8.3.1

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