Messages in this thread | | | Date | Wed, 9 Nov 2016 17:45:46 +0800 | From | Zhiyi Sun <> | Subject | Re: [PATCH] net/mlx4_en: Fix bpf_prog_add ref_cnt in mlx4 |
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On Wed, Nov 09, 2016 at 10:05:31AM +0100, Daniel Borkmann wrote: > On 11/09/2016 08:35 AM, Zhiyi Sun wrote: > > There are rx_ring_num queues. Each queue will load xdp prog. So > > bpf_prog_add() should add rx_ring_num to ref_cnt. > > > > Signed-off-by: Zhiyi Sun <zhiyisun@gmail.com> > > Your analysis looks incorrect to me. Please elaborate in more detail why > you think current code is buggy ... >
Yes, you are correct. My patch is incorrect. It is not a bug.
> Call path is dev_change_xdp_fd(), which does bpf_prog_get_type() on the > fd. This already takes a ref and only drops it in case of error. Thus > in mlx4_xdp_set(), you only need priv->rx_ring_num - 1 refs for the rest > of the rings, so that dropping refs from old_prog makes sure we release > it again. Looks correct to me (maybe a comment would have helped there). >
I thought mlx4's code is incorrect because in mlx5's driver, function mlx5e_xdp_set() calls a pair of bpf_prog_add/put, the number of add and put to the refs are same. I didn't notice that one "add" has been called in its calller. So, it seems that mlx5's code is incorrect, right?
> > drivers/net/ethernet/mellanox/mlx4/en_netdev.c | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/net/ethernet/mellanox/mlx4/en_netdev.c b/drivers/net/ethernet/mellanox/mlx4/en_netdev.c > > index 12c99a2..d25e150 100644 > > --- a/drivers/net/ethernet/mellanox/mlx4/en_netdev.c > > +++ b/drivers/net/ethernet/mellanox/mlx4/en_netdev.c > > @@ -2650,7 +2650,7 @@ static int mlx4_xdp_set(struct net_device *dev, struct bpf_prog *prog) > > */ > > if (priv->xdp_ring_num == xdp_ring_num) { > > if (prog) { > > - prog = bpf_prog_add(prog, priv->rx_ring_num - 1); > > + prog = bpf_prog_add(prog, priv->rx_ring_num); > > if (IS_ERR(prog)) > > return PTR_ERR(prog); > > } > > @@ -2680,7 +2680,7 @@ static int mlx4_xdp_set(struct net_device *dev, struct bpf_prog *prog) > > } > > > > if (prog) { > > - prog = bpf_prog_add(prog, priv->rx_ring_num - 1); > > + prog = bpf_prog_add(prog, priv->rx_ring_num); > > if (IS_ERR(prog)) > > return PTR_ERR(prog); > > } > > >
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