net: Write lock dev_base_lock without disabling bottom halves.

The writer acquires dev_base_lock with disabled bottom halves.
The reader can acquire dev_base_lock without disabling bottom halves
because there is no writer in softirq context.

On PREEMPT_RT the softirqs are preemptible and local_bh_disable() acts
as a lock to ensure that resources, that are protected by disabling
bottom halves, remain protected.
This leads to a circular locking dependency if the lock acquired with
disabled bottom halves (as in write_lock_bh()) and somewhere else with
enabled bottom halves (as by read_lock() in netstat_show()) followed by
disabling bottom halves (cxgb_get_stats() -> t4_wr_mbox_meat_timeout()
-> spin_lock_bh()). This is the reverse locking order.

All read_lock() invocation are from sysfs callback which are not invoked
from softirq context. Therefore there is no need to disable bottom
halves while acquiring a write lock.

Acquire the write lock of dev_base_lock without disabling bottom halves.

Reported-by: Pei Zhang <pezhang@redhat.com>
Reported-by: Luis Claudio R. Goncalves <lgoncalv@redhat.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 4 deletions

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 6f25c0a8aebe..d6eba554b137 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -842,9 +842,9 @@ static void set_operstate(struct net_device *dev, unsigned char transition)
 	}
 
 	if (dev->operstate != operstate) {
-		write_lock_bh(&dev_base_lock);
+		write_lock(&dev_base_lock);
 		dev->operstate = operstate;
-		write_unlock_bh(&dev_base_lock);
+		write_unlock(&dev_base_lock);
 		netdev_state_change(dev);
 	}
 }
@@ -2778,11 +2778,11 @@ static int do_setlink(const struct sk_buff *skb,
 	if (tb[IFLA_LINKMODE]) {
 		unsigned char value = nla_get_u8(tb[IFLA_LINKMODE]);
 
-		write_lock_bh(&dev_base_lock);
+		write_lock(&dev_base_lock);
 		if (dev->link_mode ^ value)
 			status |= DO_SETLINK_NOTIFY;
 		dev->link_mode = value;
-		write_unlock_bh(&dev_base_lock);
+		write_unlock(&dev_base_lock);
 	}
 
 	if (tb[IFLA_VFINFO_LIST]) {