Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753260AbcKIKUT (ORCPT ); Wed, 9 Nov 2016 05:20:19 -0500 Received: from www62.your-server.de ([213.133.104.62]:51588 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751934AbcKIKUQ (ORCPT ); Wed, 9 Nov 2016 05:20:16 -0500 Message-ID: <5822F30C.1050900@iogearbox.net> Date: Wed, 09 Nov 2016 10:57:32 +0100 From: Daniel Borkmann User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Zhiyi Sun CC: bblanco@plumgrid.com, 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 References: <20161109073544.jbufjqn7y7oa6ptg@ubuntu> <5822E6DB.40204@iogearbox.net> <20161109094546.jtmzc4xwtaavzcnt@ubuntu> In-Reply-To: <20161109094546.jtmzc4xwtaavzcnt@ubuntu> Content-Type: multipart/mixed; boundary="------------080709030105050800090703" X-Authenticated-Sender: daniel@iogearbox.net Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6648 Lines: 164 This is a multi-part message in MIME format. --------------080709030105050800090703 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit 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. --------------080709030105050800090703 Content-Type: text/x-patch; name="0001-bpf-mlx4-fix-prog-refcount-in-mlx4_en_try_alloc_reso.patch" Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename*0="0001-bpf-mlx4-fix-prog-refcount-in-mlx4_en_try_alloc_reso.pa"; filename*1="tch" >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); 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 --------------080709030105050800090703 Content-Type: text/x-patch; name="0002-bpf-mlx5-fix-prog-refcount-in-mlx5e_xdp_set.patch" Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename*0="0002-bpf-mlx5-fix-prog-refcount-in-mlx5e_xdp_set.patch" >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); if (old_prog) bpf_prog_put(old_prog); -- 1.9.3 --------------080709030105050800090703--