netdev - Re: [PATCH bpf v3] xdp: Handle device unregister for devmap

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Date:   Sat, 19 Oct 2019 13:16:23 +0200
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Martin Lau <kafai@...com>
Cc:     "daniel\@iogearbox.net" <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...com>,
        "bpf\@vger.kernel.org" <bpf@...r.kernel.org>,
        "netdev\@vger.kernel.org" <netdev@...r.kernel.org>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Subject: Re: [PATCH bpf v3] xdp: Handle device unregister for devmap_hash map type

Martin Lau <kafai@...com> writes:

> On Fri, Oct 18, 2019 at 09:44:18PM +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@...ove.SAKURA.ne.jp>
>> Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
>> ---
>> v3:
>>   - Use u32 for loop iterator variable
>>   - Since we're holding the lock we can just iterate with hlist_for_each_entry_safe()
>> v2:
>>   - Grab the update lock while walking the map and removing entries.
>> 
>>  kernel/bpf/devmap.c | 30 ++++++++++++++++++++++++++++++
>>  1 file changed, 30 insertions(+)
>> 
>> diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
>> index c0a48f336997..012dbfb0f54b 100644
>> --- a/kernel/bpf/devmap.c
>> +++ b/kernel/bpf/devmap.c
>> @@ -719,6 +719,31 @@ 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)
>> +{
>> +	unsigned long flags;
>> +	u32 i;
>> +
>> +	spin_lock_irqsave(&dtab->index_lock, flags);
>> +	for (i = 0; i < dtab->n_buckets; i++) {
>> +		struct bpf_dtab_netdev *dev;
>> +		struct hlist_head *head;
>> +		struct hlist_node *next;
>> +
>> +		head = dev_map_index_hash(dtab, i);
>> +
>> +		hlist_for_each_entry_safe(dev, next, head, index_hlist) {
>> +			if (netdev != dev->dev)
>> +				continue;
>> +
>> +			hlist_del_rcu(&dev->index_hlist);
> There is another issue...
> "dtab->items--;"

Right, of course. Thanks for your diligence in spotting my silly
mistakes! Will send a v4 :)

-Toke