Re: [PATCH net] hv_netvsc: Restore needed_headroom request
From: Vitaly Kuznetsov <vkuznets@redhat.com>
Date: 2016-02-10 10:05:58
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Vitaly Kuznetsov [off-list ref] writes:
Commit c0eb454034aa ("hv_netvsc: Don't ask for additional head room in the
skb") got rid of needed_headroom setting for the driver. With the change I
hit the following issue trying to use ptkgen module:
[ 57.522021] kernel BUG at net/core/skbuff.c:1128!
[ 57.522021] invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC
...
[ 58.721068] Call Trace:
[ 58.721068] [<ffffffffa0144e86>] netvsc_start_xmit+0x4c6/0x8e0 [hv_netvsc]
...
[ 58.721068] [<ffffffffa02f87fc>] ? pktgen_finalize_skb+0x25c/0x2a0 [pktgen]
[ 58.721068] [<ffffffff814f5760>] ? __netdev_alloc_skb+0xc0/0x100
[ 58.721068] [<ffffffffa02f9907>] pktgen_thread_worker+0x257/0x1920 [pktgen]
Basically, we're calling skb_cow_head(skb, RNDIS_AND_PPI_SIZE) and crash on
if (skb_shared(skb))
BUG();
We probably need to restore needed_headroom setting (but shrunk to
RNDIS_AND_PPI_SIZE as we don't need more) to request the required headroom
space. In theory, it should not give us performance penalty.I'm sorry for the ping but this is kind of a regression and it would be nice to have it fixed in 4.5. Here is a script to trigger kernel crash: #! /bin/sh modprobe pktgen echo "rem_device_all" > /proc/net/pktgen/kpktgend_0 echo "add_device eth0" > /proc/net/pktgen/kpktgend_0 echo "pkt_size 60" > /proc/net/pktgen/eth0 echo "clone_skb 1000000" > /proc/net/pktgen/eth0 echo "count 100000" > /proc/net/pktgen/eth0 echo "dst <SOME_IP>" > /proc/net/pktgen/eth0 echo "dst_mac <SOME_MAC>" > /proc/net/pktgen/eth0 echo "start" > /proc/net/pktgen/pgctrl cat /proc/net/pktgen/eth0 Please review.
quoted hunk
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com> --- drivers/net/hyperv/netvsc_drv.c | 3 +++ 1 file changed, 3 insertions(+)diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c index 1d3a665..98e34fe 100644 --- a/drivers/net/hyperv/netvsc_drv.c +++ b/drivers/net/hyperv/netvsc_drv.c@@ -1089,6 +1089,9 @@ static int netvsc_probe(struct hv_device *dev, net->ethtool_ops = ðtool_ops; SET_NETDEV_DEV(net, &dev->device); + /* We always need headroom for rndis header */ + net->needed_headroom = RNDIS_AND_PPI_SIZE; + /* Notify the netvsc driver of the new device */ memset(&device_info, 0, sizeof(device_info)); device_info.ring_size = ring_size;
-- Vitaly