Re: [PATCH net] net: openvswitch: silence suspicious RCU usage warning

[Eelco Chaudron]

On 30 Oct 2020, at 22:28, Jakub Kicinski wrote:

On Thu, 29 Oct 2020 15:53:21 +0100 Eelco Chaudron wrote:
Silence suspicious RCU usage warning in 
ovs_flow_tbl_masks_cache_resize()
by replacing rcu_dereference() with rcu_dereference_ovsl().

In addition, when creating a new datapath, make sure it's configured 
under
the ovs_lock.

Fixes: 9bf24f594c6a ("net: openvswitch: make masks cache size 
configurable")
Reported-by: syzbot+9a8f8bfcc56e85780...@syzkaller.appspotmail.com
Signed-off-by: Eelco Chaudron <echau...@redhat.com>
---
 net/openvswitch/datapath.c   |    8 ++++----
 net/openvswitch/flow_table.c |    2 +-
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/net/openvswitch/datapath.c b/net/openvswitch/datapath.c
index 832f898edb6a..020f8539fede 100644
--- a/net/openvswitch/datapath.c
+++ b/net/openvswitch/datapath.c
@@ -1695,6 +1695,9 @@ static int ovs_dp_cmd_new(struct sk_buff *skb, 
struct genl_info *info)
        if (err)
                goto err_destroy_ports;

+       /* So far only local changes have been made, now need the lock. */
+       ovs_lock();

Should we move the lock below assignments to param?

Looks a little strange to protect stack variables with a global lock.

You are right, I should have moved it down after the assignment. I will 
send out a v2.

        /* Set up our datapath device. */
        parms.name = nla_data(a[OVS_DP_ATTR_NAME]);
        parms.type = OVS_VPORT_TYPE_INTERNAL;
@@ -1707,9 +1710,6 @@ static int ovs_dp_cmd_new(struct sk_buff *skb, 
struct genl_info *info)
        if (err)
                goto err_destroy_meters;

-       /* So far only local changes have been made, now need the lock. */
-       ovs_lock();
-
        vport = new_vport(&parms);
        if (IS_ERR(vport)) {
                err = PTR_ERR(vport);
@@ -1725,7 +1725,6 @@ static int ovs_dp_cmd_new(struct sk_buff *skb, 
struct genl_info *info)
                                ovs_dp_reset_user_features(skb, info);
                }

-               ovs_unlock();
                goto err_destroy_meters;
        }

@@ -1742,6 +1741,7 @@ static int ovs_dp_cmd_new(struct sk_buff *skb, 
struct genl_info *info)
        return 0;

 err_destroy_meters:

Let's update the name of the label.

Guess now it is, unlock and destroy meters, so what label are you 
looking for?

err_unlock_and_destroy_meters: which looks a bit long, or just 
err_unlock:

+       ovs_unlock();
        ovs_meters_exit(dp);
 err_destroy_ports:
        kfree(dp->ports);
diff --git a/net/openvswitch/flow_table.c 
b/net/openvswitch/flow_table.c
index f3486a37361a..c89c8da99f1a 100644
--- a/net/openvswitch/flow_table.c
+++ b/net/openvswitch/flow_table.c
@@ -390,7 +390,7 @@ static struct mask_cache 
*tbl_mask_cache_alloc(u32 size)
 }
 int ovs_flow_tbl_masks_cache_resize(struct flow_table *table, u32 
size)
 {
-       struct mask_cache *mc = rcu_dereference(table->mask_cache);
+       struct mask_cache *mc = rcu_dereference_ovsl(table->mask_cache);
        struct mask_cache *new;

        if (size == mc->cache_size)