Re: [PATCH bpf] xdp: Handle device unregister for devmap_hash map type

["Toke Høiland-Jørgensen" <toke@redhat.com>]

Martin Lau <kafai@fb.com> writes:

> On Wed, Oct 16, 2019 at 03:28:02PM +0200, Toke Høiland-Jørgensen wrote:
>> It seems I forgot to add handling of devmap_hash type maps to the device
>> unregister hook for devmaps. This omission causes devices to not be
>> properly released, which causes hangs.
>> 
>> Fix this by adding the missing handler.
>> 
>> Fixes: 6f9d451ab1a3 ("xdp: Add devmap_hash map type for looking up devices by hashed index")
>> Reported-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
>> Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
>> ---
>>  kernel/bpf/devmap.c | 34 ++++++++++++++++++++++++++++++++++
>>  1 file changed, 34 insertions(+)
>> 
>> diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
>> index d27f3b60ff6d..deb9416341e9 100644
>> --- a/kernel/bpf/devmap.c
>> +++ b/kernel/bpf/devmap.c
>> @@ -719,6 +719,35 @@ const struct bpf_map_ops dev_map_hash_ops = {
>>  	.map_check_btf = map_check_no_btf,
>>  };
>>  
>> +static void dev_map_hash_remove_netdev(struct bpf_dtab *dtab,
>> +				       struct net_device *netdev)
>> +{
>> +	int i;
>> +
>> +	for (i = 0; i < dtab->n_buckets; i++) {
>> +		struct bpf_dtab_netdev *dev, *odev;
>> +		struct hlist_head *head;
>> +
>> +		head = dev_map_index_hash(dtab, i);
>> +		dev = hlist_entry_safe(rcu_dereference_raw(hlist_first_rcu(head)),
>> +				       struct bpf_dtab_netdev,
>> +				       index_hlist);
>> +
>> +		while (dev) {
>> +			odev = (netdev == dev->dev) ? dev : NULL;
>> +			dev = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(&dev->index_hlist)),
>> +					       struct bpf_dtab_netdev,
>> +					       index_hlist);
>> +
>> +			if (odev) {
>> +				hlist_del_rcu(&odev->index_hlist);
> Would it race with the dev_map_hash's update/delete side?

Oh, right, seems I forgot to grab the lock; will send a v2!

-Toke