On 2021-11-25 11:01:10 [+0100], To Luis Goncalves wrote:
>
> It makes sense to only change that one invocation. Let me form a patch.
So I made dis:
| From aaef7596167b3b38a81567af81aaa2f9559c91df Mon Sep 17 00:00:00 2001
| From: "Luis Claudio R. Goncalves" <lgoncalv@xxxxxxxxxx>
| Date: Thu, 25 Nov 2021 11:05:17 +0100
| Subject: [PATCH] net-sysfs: Acquire dev_base_lock disabled BH in
| netstat_show()
|
| 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. Also readers can acquire
| the lock in task and softirq context and multiple readers are allowed.
|
| 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.
|
| In order to avoid the reverse locking order, acquire the dev_base_lock
| with disabled bottom halves.
|
| Reported-by: Pei Zhang <pezhang@xxxxxxxxxx>
| Signed-off-by: Luis Claudio R. Goncalves <lgoncalv@xxxxxxxxxx>
| Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
and then I started locking for in-softirq reader or writer. I can't find
any. Therefore I made this for testing:
diff --git a/net/core/dev.c b/net/core/dev.c
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -371,12 +371,12 @@ static void list_netdevice(struct net_device *dev)
ASSERT_RTNL();
- write_lock_bh(&dev_base_lock);
+ write_lock(&dev_base_lock);
list_add_tail_rcu(&dev->dev_list, &net->dev_base_head);
netdev_name_node_add(net, dev->name_node);
hlist_add_head_rcu(&dev->index_hlist,
dev_index_hash(net, dev->ifindex));
- write_unlock_bh(&dev_base_lock);
+ write_unlock(&dev_base_lock);
dev_base_seq_inc(net);
}
@@ -389,11 +389,11 @@ static void unlist_netdevice(struct net_device *dev)
ASSERT_RTNL();
/* Unlink dev from the device chain */
- write_lock_bh(&dev_base_lock);
+ write_lock(&dev_base_lock);
list_del_rcu(&dev->dev_list);
netdev_name_node_del(dev->name_node);
hlist_del_rcu(&dev->index_hlist);
- write_unlock_bh(&dev_base_lock);
+ write_unlock(&dev_base_lock);
dev_base_seq_inc(dev_net(dev));
}
@@ -1272,15 +1272,15 @@ int dev_change_name(struct net_device *dev, const char *newname)
netdev_adjacent_rename_links(dev, oldname);
- write_lock_bh(&dev_base_lock);
+ write_lock(&dev_base_lock);
netdev_name_node_del(dev->name_node);
- write_unlock_bh(&dev_base_lock);
+ write_unlock(&dev_base_lock);
synchronize_rcu();
- write_lock_bh(&dev_base_lock);
+ write_lock(&dev_base_lock);
netdev_name_node_add(net, dev->name_node);
- write_unlock_bh(&dev_base_lock);
+ write_unlock(&dev_base_lock);
ret = call_netdevice_notifiers(NETDEV_CHANGENAME, dev);
ret = notifier_to_errno(ret);
diff --git a/net/core/link_watch.c b/net/core/link_watch.c
--- a/net/core/link_watch.c
+++ b/net/core/link_watch.c
@@ -55,7 +55,7 @@ static void rfc2863_policy(struct net_device *dev)
if (operstate == dev->operstate)
return;
- write_lock_bh(&dev_base_lock);
+ write_lock(&dev_base_lock);
switch(dev->link_mode) {
case IF_LINK_MODE_TESTING:
@@ -74,7 +74,7 @@ static void rfc2863_policy(struct net_device *dev)
dev->operstate = operstate;
- write_unlock_bh(&dev_base_lock);
+ write_unlock(&dev_base_lock);
}
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
--- 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);
}
}
@@ -2779,11 +2779,11 @@ 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]) {
diff --git a/net/hsr/hsr_device.c b/net/hsr/hsr_device.c
--- a/net/hsr/hsr_device.c
+++ b/net/hsr/hsr_device.c
@@ -30,13 +30,13 @@ static bool is_slave_up(struct net_device *dev)
static void __hsr_set_operstate(struct net_device *dev, int transition)
{
- write_lock_bh(&dev_base_lock);
+ write_lock(&dev_base_lock);
if (dev->operstate != transition) {
dev->operstate = transition;
- write_unlock_bh(&dev_base_lock);
+ write_unlock(&dev_base_lock);
netdev_state_change(dev);
} else {
- write_unlock_bh(&dev_base_lock);
+ write_unlock(&dev_base_lock);
}
}
If this does not create any warnings (with or without RT) then I would
suggest to remove that _bh suffix since there is no need for it. This
should also fix the RT warning you see now.
Agreed?
Sebastian
