Date: Thu, 13 Feb 2014 11:05:31 +0200 From: Viktor Penkoff <vpenkoff@gmail.com> To: freebsd-hackers@freebsd.org Subject: Receiving jumbo frames Message-ID: <CAE-a5gZZp=G8pDGh_%2B%2Bf4bKMcgqM=F-dqrROwr2Xmq1VyLZRLA@mail.gmail.com>
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Hi, folks! I'm writing an extension functionality to not-yet published
network driver.
I'm receiving the typical ethernet frames without problems. Considering the
datasheet of the device,
I'm capable of receiving jumbo frames. When I try to do that, e.g. to send
jumbo frame of 8000 bytes, I'm receiving only a limited count of them -
105, then the kernel crashes with the following message:
"panic: vm_fault: fault on nofault entry, addr: cfcec000".
I have inspected a kernel dump with kgdb and the problem occurs at the
function bus_dmamap_sync.
The line that the panic happens is in a standard invoking receive
interrupt function. Packet data is stored in memory buffers, with any
single packet spanning multiple buffers if necessary. The buffers are
allocated by the CPU and are managed through chained descriptor lists.
When I'm sending jumbo packets, e.g. 8008 bytes in size each, due to live
debugging with jtag and kgdb, I've got the following information for the
mbuf:
% ping -I eth0 -c 1 -s 8000 -M dont A.B.C.D -v -p ff
{m_hdr =3D {mh_next =3D 0x0, mh_nextpkt =3D 0x0, mh_data =3D 0xc3d41800 "",
mh_len =3D 2048, mh_flags =3D 3, mh_type =3D 1, pad =3D "\000"}, M_dat =
=3D {
MH =3D {MH_pkthdr =3D {rcvif =3D 0x0, header =3D 0x0, len =3D 2048, flo=
wid =3D 0,
csum_flags =3D 0, csum_data =3D 0, tso_segsz =3D 0, PH_vt =3D {
vt_vtag =3D 0, vt_nrecs =3D 0}, tags =3D {slh_first =3D 0x0},
dsa_tag =3D {0, 0}}, MH_dat =3D {MH_ext =3D {ext_buf =3D 0xc3d41800=
"",
ext_free =3D 0, ext_arg1 =3D 0x0, ext_arg2 =3D 0x0, ext_size =3D =
2048,
ref_cnt =3D 0xc3d3f244, ext_type =3D 6},
In this case, the given mbuf must occupy ~4 descriptors, IMO. Following the
next pointer in the descriptor list shows that the CPU has
an ownership. Nevertheless, =F2he byte count of the received frame shows th=
at
8056 bytes are received.
More interesting is the fact that an echo reply is given back. But after a
constant count of received packets, the kernel hangs.
Some background information:
To enable the jumbo frame, one must set the appropriate register.
At the software level, a ring buffer with the descriptors is implemented.
The device, under which the driver runs, is arm-based.
The freebsd version is 8.0. The device uses SerialDMA queues for
transmitting and receiving.
To receive packets, the CPU must perform the following:
1. Prepare a linked list of descriptors
2. Configure a given queue with the address of the first descriptor in
the list,
3. enable SerialDMA;
With the transmission - I don't have any problems. The logic is the same as
by the reception of packets - ring buffer with descriptors.
Any ideas what can cause this type of crashes?
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