Re: [PATCH] cnic: don't take the rtnl_read_lock in cnic_rcv_netevent
From: Michael Chan <mchan@broadcom.com>
Date: 2014-05-30 17:58:12
On Fri, 2014-05-30 at 11:00 -0400, Neil Horman wrote:
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
Because the bnx2fc function can sleep, we need a more complete fix to prevent the ulp_ops from going away when the device is unregistered. synchronize_rcu() won't be able to protect it. I'll post the patch later today. Thanks.
quoted hunk ↗ jump to hunk
Signed-off-by: Neil Horman <nhorman@tuxdriver.com> CC: "David S. Miller" <davem@davemloft.net> CC: Michael Chan <mchan@broadcom.com> CC: fcoe-devel@open-fcoe.org CC: Robert Love <redacted> CC: Vasu Dev <redacted> --- 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 */