Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754504AbcKIRGU (ORCPT ); Wed, 9 Nov 2016 12:06:20 -0500 Received: from mail-pf0-f181.google.com ([209.85.192.181]:36299 "EHLO mail-pf0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754140AbcKIRGS (ORCPT ); Wed, 9 Nov 2016 12:06:18 -0500 Date: Wed, 9 Nov 2016 09:06:15 -0800 From: Brenden Blanco To: Daniel Borkmann Cc: Zhiyi Sun , Tariq Toukan , Yishai Hadas , netdev@vger.kernel.org, linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org, alexei.starovoitov@gmail.com Subject: Re: [PATCH] net/mlx4_en: Fix bpf_prog_add ref_cnt in mlx4 Message-ID: <20161109170615.GB10428@gmail.com> References: <20161109073544.jbufjqn7y7oa6ptg@ubuntu> <5822E6DB.40204@iogearbox.net> <20161109094546.jtmzc4xwtaavzcnt@ubuntu> <5822F30C.1050900@iogearbox.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5822F30C.1050900@iogearbox.net> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6508 Lines: 148 On Wed, Nov 09, 2016 at 10:57:32AM +0100, Daniel Borkmann wrote: > On 11/09/2016 10:45 AM, Zhiyi Sun wrote: > >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 > >> > >>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? > > Yep, I think the two attached patches are needed. > > The other thing I noticed in mlx5e_create_rq() is that it calls > bpf_prog_add(rq->xdp_prog, 1) without actually checking for errors. > From d2bd6b3cd8636716a06b0ea3b1e041e16f87cce0 Mon Sep 17 00:00:00 2001 > Message-Id: > From: Daniel Borkmann > Date: Wed, 9 Nov 2016 10:31:19 +0100 > Subject: [PATCH net-next 1/2] bpf, mlx4: fix prog refcount in mlx4_en_try_alloc_resources error path > > Commit 67f8b1dcb9ee ("net/mlx4_en: Refactor the XDP forwarding rings > scheme") added a bug in that the prog's reference count is not dropped > in the error path when mlx4_en_try_alloc_resources() is failing. > > We previously took bpf_prog_add(prog, priv->rx_ring_num - 1), that we > need to release again. Earlier in the call-path, dev_change_xdp_fd() > itself holds a ref to the prog as well, which is then released though > bpf_prog_put() due to the propagated error. > > Fixes: 67f8b1dcb9ee ("net/mlx4_en: Refactor the XDP forwarding rings scheme") > Signed-off-by: Daniel Borkmann > --- > drivers/net/ethernet/mellanox/mlx4/en_netdev.c | 5 ++++- > include/linux/bpf.h | 1 + > kernel/bpf/syscall.c | 11 +++++++++++ > 3 files changed, 16 insertions(+), 1 deletion(-) > > diff --git a/drivers/net/ethernet/mellanox/mlx4/en_netdev.c b/drivers/net/ethernet/mellanox/mlx4/en_netdev.c > index 0f6225c..4104aec 100644 > --- a/drivers/net/ethernet/mellanox/mlx4/en_netdev.c > +++ b/drivers/net/ethernet/mellanox/mlx4/en_netdev.c > @@ -2747,8 +2747,11 @@ static int mlx4_xdp_set(struct net_device *dev, struct bpf_prog *prog) > } > > err = mlx4_en_try_alloc_resources(priv, tmp, &new_prof); > - if (err) > + if (err) { > + if (prog) > + bpf_prog_add_undo(prog, priv->rx_ring_num - 1); Why not just move the above bpf_prog_add to be below the try_alloc? Nobody needs those references until all of the resources have been allocated, and then we can remove the need for bpf_prog_add_undo. > goto unlock_out; > + } > > if (priv->port_up) { > port_up = 1; > diff --git a/include/linux/bpf.h b/include/linux/bpf.h > index edcd96d..4f6a4f1 100644 > --- a/include/linux/bpf.h > +++ b/include/linux/bpf.h > @@ -234,6 +234,7 @@ u64 bpf_event_output(struct bpf_map *map, u64 flags, void *meta, u64 meta_size, > struct bpf_prog *bpf_prog_get(u32 ufd); > struct bpf_prog *bpf_prog_get_type(u32 ufd, enum bpf_prog_type type); > struct bpf_prog *bpf_prog_add(struct bpf_prog *prog, int i); > +void bpf_prog_add_undo(struct bpf_prog *prog, int i); > struct bpf_prog *bpf_prog_inc(struct bpf_prog *prog); > void bpf_prog_put(struct bpf_prog *prog); > > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c > index 228f962..a6e4dd8 100644 > --- a/kernel/bpf/syscall.c > +++ b/kernel/bpf/syscall.c > @@ -680,6 +680,17 @@ struct bpf_prog *bpf_prog_add(struct bpf_prog *prog, int i) > } > EXPORT_SYMBOL_GPL(bpf_prog_add); > > +void bpf_prog_add_undo(struct bpf_prog *prog, int i) > +{ > + /* Only to be used for undoing previous bpf_prog_add() in some > + * error path. We still know that another entity in our call > + * path holds a reference to the program, thus atomic_sub() can > + * be safely used here! > + */ > + atomic_sub(i, &prog->aux->refcnt); > +} > +EXPORT_SYMBOL_GPL(bpf_prog_add_undo); > + > struct bpf_prog *bpf_prog_inc(struct bpf_prog *prog) > { > return bpf_prog_add(prog, 1); > -- > 1.9.3 > > From f0789544432bbb89c53c3b8ac6575d48fed97786 Mon Sep 17 00:00:00 2001 > Message-Id: > In-Reply-To: > References: > From: Daniel Borkmann > Date: Wed, 9 Nov 2016 10:51:26 +0100 > Subject: [PATCH net-next 2/2] bpf, mlx5: fix prog refcount in mlx5e_xdp_set > > dev_change_xdp_fd() already holds a reference, so bpf_prog_add(prog, 1) > is not correct as it takes one reference too much and will thus leak > the prog eventually. Also, bpf_prog_add() can fail and is not checked > for errors here. > > Fixes: 86994156c736 ("net/mlx5e: XDP fast RX drop bpf programs support") > Signed-off-by: Daniel Borkmann > --- > drivers/net/ethernet/mellanox/mlx5/core/en_main.c | 2 -- > 1 file changed, 2 deletions(-) > > diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c > index ba0c774..63309dd 100644 > --- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c > +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c > @@ -3121,8 +3121,6 @@ static int mlx5e_xdp_set(struct net_device *netdev, struct bpf_prog *prog) > > /* exchange programs */ > old_prog = xchg(&priv->xdp_prog, prog); > - if (prog) > - bpf_prog_add(prog, 1); There is also another use of bpf_prog_add down below, which does not check the error return. Same in mlx5e_create_rq. > if (old_prog) > bpf_prog_put(old_prog); > > -- > 1.9.3 >