Re: [PATCH] bpf: devmap: Pass lockdep expression to RCU lists

[Jesper Dangaard Brouer]

On Thu, 23 Jan 2020 17:34:38 +0530
Amol Grover <frextrite@xxxxxxxxx> wrote:

> head is traversed using hlist_for_each_entry_rcu outside an
> RCU read-side critical section but under the protection
> of dtab->index_lock.

We do hold the lock in update and delete cases, but not in the lookup
cases.  Is it then still okay to add the lockdep_is_held() annotation?

If it is then it looks fine to me:

Acked-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
 
> Hence, add corresponding lockdep expression to silence false-positive
> lockdep warnings, and harden RCU lists.
> 
> Signed-off-by: Amol Grover <frextrite@xxxxxxxxx>
> ---
>  kernel/bpf/devmap.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
> index 3d3d61b5985b..b4b6b77f309c 100644
> --- a/kernel/bpf/devmap.c
> +++ b/kernel/bpf/devmap.c
> @@ -293,7 +293,8 @@ struct bpf_dtab_netdev *__dev_map_hash_lookup_elem(struct bpf_map *map, u32 key)
>  	struct hlist_head *head = dev_map_index_hash(dtab, key);
>  	struct bpf_dtab_netdev *dev;
>  
> -	hlist_for_each_entry_rcu(dev, head, index_hlist)
> +	hlist_for_each_entry_rcu(dev, head, index_hlist,
> +				 lockdep_is_held(&dtab->index_lock))
>  		if (dev->idx == key)
>  			return dev;
>  

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer