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

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Message-ID: <20191018211818.5e6gfdjwq4zefnez@kafai-mbp>
Date:   Fri, 18 Oct 2019 21:18:21 +0000
From:   Martin Lau <kafai@...com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
CC:     "daniel@...earbox.net" <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...com>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "netdev@...r.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

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--;"

> +			call_rcu(&dev->rcu, __dev_map_entry_free);
> +		}
> +	}
> +	spin_unlock_irqrestore(&dtab->index_lock, flags);
> +}
> +
>  static int dev_map_notification(struct notifier_block *notifier,
>  				ulong event, void *ptr)
>  {
> @@ -735,6 +760,11 @@ static int dev_map_notification(struct notifier_block *notifier,
>  		 */
>  		rcu_read_lock();
>  		list_for_each_entry_rcu(dtab, &dev_map_list, list) {
> +			if (dtab->map.map_type == BPF_MAP_TYPE_DEVMAP_HASH) {
> +				dev_map_hash_remove_netdev(dtab, netdev);
> +				continue;
> +			}
> +
>  			for (i = 0; i < dtab->map.max_entries; i++) {
>  				struct bpf_dtab_netdev *dev, *odev;
>  
> -- 
> 2.23.0
>