From: "Björn Töpel" <bjorn.topel@gmail.com>
To: ast@kernel.org, daniel@iogearbox.net, netdev@vger.kernel.org,
bpf@vger.kernel.org
Cc: "Björn Töpel" <bjorn.topel@intel.com>,
jonathan.lemon@gmail.com, yhs@fb.com, weqaar.janjua@gmail.com,
magnus.karlsson@intel.com, weqaar.a.janjua@intel.com
Subject: [PATCH bpf v2] net, xsk: Avoid taking multiple skbuff references
Date: Mon, 23 Nov 2020 18:56:00 +0100 [thread overview]
Message-ID: <20201123175600.146255-1-bjorn.topel@gmail.com> (raw)
From: Björn Töpel <bjorn.topel@intel.com>
Commit 642e450b6b59 ("xsk: Do not discard packet when NETDEV_TX_BUSY")
addressed the problem that packets were discarded from the Tx AF_XDP
ring, when the driver returned NETDEV_TX_BUSY. Part of the fix was
bumping the skbuff reference count, so that the buffer would not be
freed by dev_direct_xmit(). A reference count larger than one means
that the skbuff is "shared", which is not the case.
If the "shared" skbuff is sent to the generic XDP receive path,
netif_receive_generic_xdp(), and pskb_expand_head() is entered the
BUG_ON(skb_shared(skb)) will trigger.
This patch adds a variant to dev_direct_xmit(), __dev_direct_xmit(),
where a user can select the skbuff free policy. This allows AF_XDP to
avoid bumping the reference count, but still keep the NETDEV_TX_BUSY
behavior.
Reported-by: Yonghong Song <yhs@fb.com>
Fixes: 642e450b6b59 ("xsk: Do not discard packet when NETDEV_TX_BUSY")
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
---
v2:
Removed the bool parameter, and inlined dev_direct_xmit(). (Daniel)
---
include/linux/netdevice.h | 11 ++++++++++-
net/core/dev.c | 8 ++------
net/xdp/xsk.c | 8 +-------
3 files changed, 13 insertions(+), 14 deletions(-)
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 964b494b0e8d..bd841f31dfab 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -2815,7 +2815,16 @@ u16 dev_pick_tx_cpu_id(struct net_device *dev, struct sk_buff *skb,
struct net_device *sb_dev);
int dev_queue_xmit(struct sk_buff *skb);
int dev_queue_xmit_accel(struct sk_buff *skb, struct net_device *sb_dev);
-int dev_direct_xmit(struct sk_buff *skb, u16 queue_id);
+int __dev_direct_xmit(struct sk_buff *skb, u16 queue_id);
+static inline int dev_direct_xmit(struct sk_buff *skb, u16 queue_id)
+{
+ int ret;
+
+ ret = __dev_direct_xmit(skb, queue_id);
+ if (!dev_xmit_complete(ret))
+ kfree_skb(skb);
+ return ret;
+}
int register_netdevice(struct net_device *dev);
void unregister_netdevice_queue(struct net_device *dev, struct list_head *head);
void unregister_netdevice_many(struct list_head *head);
diff --git a/net/core/dev.c b/net/core/dev.c
index 82dc6b48e45f..8588ade790cb 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4180,7 +4180,7 @@ int dev_queue_xmit_accel(struct sk_buff *skb, struct net_device *sb_dev)
}
EXPORT_SYMBOL(dev_queue_xmit_accel);
-int dev_direct_xmit(struct sk_buff *skb, u16 queue_id)
+int __dev_direct_xmit(struct sk_buff *skb, u16 queue_id)
{
struct net_device *dev = skb->dev;
struct sk_buff *orig_skb = skb;
@@ -4210,17 +4210,13 @@ int dev_direct_xmit(struct sk_buff *skb, u16 queue_id)
dev_xmit_recursion_dec();
local_bh_enable();
-
- if (!dev_xmit_complete(ret))
- kfree_skb(skb);
-
return ret;
drop:
atomic_long_inc(&dev->tx_dropped);
kfree_skb_list(skb);
return NET_XMIT_DROP;
}
-EXPORT_SYMBOL(dev_direct_xmit);
+EXPORT_SYMBOL(__dev_direct_xmit);
/*************************************************************************
* Receiver routines
diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index 5a6cdf7b320d..b7b039bd9d03 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -411,11 +411,7 @@ static int xsk_generic_xmit(struct sock *sk)
skb_shinfo(skb)->destructor_arg = (void *)(long)desc.addr;
skb->destructor = xsk_destruct_skb;
- /* Hinder dev_direct_xmit from freeing the packet and
- * therefore completing it in the destructor
- */
- refcount_inc(&skb->users);
- err = dev_direct_xmit(skb, xs->queue_id);
+ err = __dev_direct_xmit(skb, xs->queue_id);
if (err == NETDEV_TX_BUSY) {
/* Tell user-space to retry the send */
skb->destructor = sock_wfree;
@@ -429,12 +425,10 @@ static int xsk_generic_xmit(struct sock *sk)
/* Ignore NET_XMIT_CN as packet might have been sent */
if (err == NET_XMIT_DROP) {
/* SKB completed but not sent */
- kfree_skb(skb);
err = -EBUSY;
goto out;
}
- consume_skb(skb);
sent_frame = true;
}
base-commit: 178648916e73e00de83150eb0c90c0d3a977a46a
--
2.27.0
next reply other threads:[~2020-11-23 17:56 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-23 17:56 Björn Töpel [this message]
2020-11-24 21:50 ` [PATCH bpf v2] net, xsk: Avoid taking multiple skbuff references Daniel Borkmann
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