[Gluster-devel] Possible bug in the communications layer ?

Thu Apr 28 16:42:32 UTC 2016

Hi Niels, 

On 28.04.2016 15:44, Niels de Vos wrote: 

> On Thu, Apr
28, 2016 at 02:43:01PM +0200, Xavier Hernandez wrote:
> 
>> Hi, I've
seen what seems a bug in the communications layer. The first sign is an
"XDR decoding failed" error in the logs. This happens with Gluster
3.7.11 accessed through Ganesha and gfapi. The volume is a
distributed-disperse 4*(4+2). I'm able to reproduce the problem easily
doing the following test: iozone -t2 -s10g -r1024k -i0 -w
-F/iozone{1..2}.dat echo 3 >/proc/sys/vm/drop_caches iozone -t2 -s10g
-r1024k -i1 -w -F/iozone{1..2}.dat The error happens soon after starting
the read test.
> 
> Do you know if this only happens on disperse
volumes, or also with
> others?

I have only seen the problem with EC.
Not sure if it's because I do most of my tests with EC or because other
volumes do not manifest this problem. However I've only seen this when I
started testing Ganesha. I have never seen the problem with FUSE.

I
think the reason is that FUSE is slower than Ganesha (little more than
120 MB/s vs 400 MB/s) and the combination of events needed to cause this
problem would be much more unlikely to happen on FUSE. Since EC also
talks to many bricks simultaneously (6 in this case), maybe this makes
it more sensible to communications problems compared to a replicated
volume.

> If you have captured a network trace, could you provide it
to
> me? You can use 'editcap -s0 ...' to copy only the relevant
packets.
> But, I dont have an issue to download a few GB either if that
is easier
> for you.
> 
>> As can be seen in the data below,
client3_3_readv_cbk() is processing an iovec of 116 bytes, however it
should be of 154 bytes (the buffer in memory really seems to contain 154
bytes). The data on the network seems ok (at least I haven't been able
to identify any problem), so this must be a processing error on the
client side. The last field in cut buffer of the sequentialized data
corresponds to the length of the xdata field: 0x26. So at least 38 more
byte should be present. My guess is that some corner case is hit reading
fragmented network packets due to a high load. Debug information:
Breakpoint 1, client3_3_readv_cbk (req=0x7f540e64106c,
iov=0x7f540e6410ac, count=, myframe=0x7f54259a4d54) at
client-rpc-fops.c:3021 3021 gf_msg (this->name, GF_LOG_ERROR, EINVAL,
(gdb) print *iov $1 = {iov_base = 0x7f53e994e018, iov_len = 116} (gdb)
x/116xb 0x7f53e994e018 0x7f53e994e018: 0x00 0x00 0x80 0x00 0x00 0x00
0x00 0x00 0x7f53e994e020: 0xa8 0xbf 0xa3 0xe0 0x5f 0x48 0x4c 0x1e
> 
>
Hmm, I'm not sure how this is layed out in memory. 0x80 would be one
of
> first bytes in RPC payload, it signals 'last record' for the RPC
>
procedure, and we only send one record anyway. The four bytes combined
>
like (0x80 0x.. 0x.. 0x..) should be (0x80 | rpc-record-size). Reading
>
this in Wireshark from a .pcap.gz is much easier :)

The RPC header is
already decoded here. The 116 bytes are only the content of the readv
answer, as decoded by xdr_gfs3_read_rsp() function.

This means that the
first 4 bytes are the op_ret, next 4 are op_errno, followed by an
encoded iatt (with gfid and ino number as the first fields). Then a size
field and the length of a stream of bytes (corresponding to the encoded
xdata).

I've a network capture. I can upload it if you want, but I
think this is what you are trying to see:

(gdb) f 1
#1
0x00007fa88cb5bab0 in rpc_clnt_handle_reply
(clnt=clnt at entry=0x7fa870413e30, pollin=pollin at entry=0x7fa86400efe0) at
rpc-clnt.c:764
764 req->cbkfn (req, req->rsp, req->rspcnt,
saved_frame->frame);
(gdb) print *pollin
$1 = {vector = {{iov_base =
0x7fa7ef580000, iov_len = 140}, {iov_base = 0x7fa7ef460000, iov_len =
32808}, {iov_base = 0x0, iov_len = 0} <repeats 14 times>}, count = 2,

vectored = 1 '01', private = 0x7fa86c00ec60, iobref = 0x7fa86400e560,
hdr_iobuf = 0x7fa868022ee0, is_reply = 1 '01'}
(gdb) x/140xb
0x7fa7ef580000
0x7fa7ef580000: 0x00 0x00 0x89 0x68 0x00 0x00 0x00
0x01
0x7fa7ef580008: 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00
0x7fa7ef580010: 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00
0x7fa7ef580018: 0x00 0x00 0x80 0x00 0x00 0x00 0x00
0x00
0x7fa7ef580020: 0xc3 0x8e 0x35 0xf0 0x31 0xa1 0x45
0x01
0x7fa7ef580028: 0x8a 0x21 0x06 0x4b 0x08 0x4c 0x59
0xdf
0x7fa7ef580030: 0x8a 0x21 0x06 0x4b 0x08 0x4c 0x59
0xdf
0x7fa7ef580038: 0x00 0x00 0x00 0x00 0x00 0x00 0x08
0x00
0x7fa7ef580040: 0x00 0x00 0x81 0xa0 0x00 0x00 0x00
0x01
0x7fa7ef580048: 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00
0x7fa7ef580050: 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00
0x7fa7ef580058: 0x00 0x00 0x00 0x00 0xa0 0x00 0x00
0x00
0x7fa7ef580060: 0x00 0x00 0x10 0x00 0x00 0x00 0x00
0x00
0x7fa7ef580068: 0x00 0x50 0x00 0x00 0x57 0x22 0x33
0x1f
0x7fa7ef580070: 0x24 0x0c 0xc2 0x58 0x57 0x22 0x33
0xa1
0x7fa7ef580078: 0x34 0x11 0x3b 0x54 0x57 0x22 0x33
0xa1
0x7fa7ef580080: 0x34 0x20 0x7d 0x7a 0x00 0x00 0x80
0x00
0x7fa7ef580088: 0x00 0x00 0x00 0x26

(gdb) f 3
#3
0x00007fa88cb57853 in rpc_transport_notify
(this=this at entry=0x7fa870423ab0,
event=event at entry=RPC_TRANSPORT_MSG_RECEIVED,
data=data at entry=0x7fa86400efe0) at rpc-transport.c:546
546 ret =
this->notify (this, this->mydata, event, data);
(gdb) print *this
$3 =
{ops = 0x7fa87ff76740 <tops>, listener = 0x0, private = 0x7fa870424750,
xl_private = 0x0, xl = 0x7fa87000b5a0, mydata = 0x7fa870413e60, lock =
{__data = {__lock = 0,
 __count = 0, __owner = 0, __nusers = 0, __kind =
0, __spins = 0, __list = {__prev = 0x0, __next = 0x0}}, __size = '00'
<repeats 39 times>, __align = 0}, refcount = 2,
 outstanding_rpc_count =
0, ctx = 0x2688740, options = 0x7fa88788529c, name = 0x7fa8704245f0
"test-client-2", dnscache = 0x7fa870472b90, drc_client = 0x0, buf =
0x0,
 init = 0x7fa87fd6b760 <init>, fini = 0x7fa87fd6b690 <fini>,
reconfigure = 0x7fa87fd6b290 <reconfigure>, notify = 0x7fa88cb5bbb0
<rpc_clnt_notify>, notify_data = 0x0, peerinfo = {
 sockaddr =
{ss_family = 2, __ss_align = 0, __ss_padding = '00' <repeats 111
times>}, sockaddr_len = 16, identifier = "193.109.174.232:49152", '00'
<repeats 86 times>,
 max_op_version = 0, min_op_version = 0, volname =
'00' <repeats 1023 times>}, myinfo = {sockaddr = {ss_family = 2,
__ss_align = 0,
 __ss_padding = '00' <repeats 111 times>}, sockaddr_len
= 16, identifier = "193.109.174.230:65205", '00' <repeats 86 times>,
max_op_version = 0, min_op_version = 0,
 volname = '00' <repeats 1023
times>}, total_bytes_read = 390116824, total_bytes_write = 5374554184,
list = {next = 0x7fa870424568, prev = 0x7fa870424568}, bind_insecure =
1,
 dl_handle = 0x26efad0, ssl_name = 0x0, clnt_options = 0x0}

The
first 4 bytes of the dump correspond to the XID of the answer (0x8968).
We can see that the answer comes from 193.109.174.232:49152. The output
of the following command is attached:

# tshark -r tcpdump.pcap -n -V -Y
"rpc.xid == 0x8968 and ip.addr == 193.109.174.232 and tcp.port ==
49152"

We can see that the answer is received in two TCP segments: one
of 116 bytes and the other of 32836 bytes. Probably this is the source
of the problem.

Don't hesitate to file a bug for this, and include the
exact error
messages you get. If possible w> ; 
> 
> I'll file a bug
with all this information.
> 
> Thanks,
> 
> Xavi
:100%">

Thanks,
Niels
 0x7f53e994e028: 0x80 0xa3 0x8a 0xd8 0x9d 0xa1 0x1c 0x75
0x7f53e994e030: 0x80 0xa3 0x8a 0xd8 0x9d 0xa1 0x1c 0x75 0x7f53e994e038:
0x00 0x00 0x00 0x00 0x00 0x00 0x08 0x00 0x7f53e994e040: 0x00 0x00 0x81
0xa0

> x00 0x00 0x00 0x00 0x00 0x7f53e994e058: 0x00 0x00 0x00 0x00 0xa0
0x00 0x00 0x00 0x7f53e994e060: 0x00 0x00 0x10 0x00 0x00 0x00 0x00 0x00
0x7f53e994e068: 0x00 0x50 0x00 0x00 0x57 0x22 0x04 0x1f 0x7f53e994e070:
0x25 0x38 0x92 0x91 0x57 0x22 0x04 0xb3 0x7f53e994e078: 0x03 0x53 0x1b
0x13 0x57 0x22 0x04 0xb3 0x7f53e994e080: 0x06 0xf5 0xe1 0x99 0x00 0x00
0x80 0x00 0x7f53e994e088: 0x00 0x00 0x00 0x26 (gdb) x/154xb
0x7f53e994e018 0x7f53e994e018: 0x00 0x00 0x80 0x00 0x00 0x00 0x00 0x00
0x7f53e994e020: 0xa8 0xbf 0xa3 0xe0 0x5f 0x48 0x4c 0x1e 0x7f53e994e028:
0x80 0xa3 0x8a 0xd8 0x9d 0xa1 0x1c 0x75 0x7f53e994e030: 0x80 0xa3 0x8a
0xd8 0x9d 0xa1 0x1c 0x75 0x7f53e994e038: 0x00 0x00 0x00 0x00 0x00 0x00
0x08 0x00 0x7f53e994e040: 0x00 0x00 0x81 0xa0 0x00 0x00 0x00 0x01
0x7f53e994e048: 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x7f53e994e050:
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x7f53e994e058: 0x00 0x00 0x00
0x00 0xa0 0x00 0x00 0x00 0x7f53e994e060: 0x00 0x00 0x10 0x00 0x00 0x00
0x00 0x00 0x7f53e994e068: 0x00 0x50 0x00 0x00 0x57 0x22 0x04 0x1f
0x7f53e994e070: 0x25 0x38 0x92 0x91 0x57 0x22 0x04 0xb3 0x7f53e994e078:
0x03 0x53 0x1b 0x13 0x57 0x22 0x04 0xb3 0x7f53e994e080: 0x06 0xf5 0xe1
0x99 0x00 0x00 0x80 0x00 0x7f53e994e088: 0x00 0x00 0x00 0x26 0x00 0x00
0x00 0x01 0x7f53e994e090: 0x00 0x00 0x00 0x17 0x00 0x00 0x00 0x02
0x7f53e994e098: 0x67 0x6c 0x75 0x73 0x74 0x65 0x72 0x66 0x7f53e994e0a0:
0x73 0x2e 0x69 0x6e 0x6f 0x64 0x65 0x6c 0x7f53e994e0a8: 0x6b 0x2d 0x63
0x6f 0x75 0x6e 0x74 0x00 0x7f53e994e0b0: 0x31 0x00 (gdb) bt #0
client3_3_readv_cbk (req=0x7f540e64106c, iov=0x7f540e6410ac, count=,
myframe=0x7f54259a4d54) at client-rpc-fops.c:3021 #1 0x00007f542a677ab0
in rpc_clnt_handle_reply (clnt=clnt at entry=0x7f54101cdef0,
pollin=pollin at entry=0x7f54000091f0) at rpc-clnt.c:764 #2
0x00007f542a677d6f in rpc_clnt_notify (trans=, mydata=0x7f54101cdf20,
event=, data=0x7f54000091f0) at rpc-clnt.c:925 #3 0x00007f542a673853 in
rpc_transport_notify (this=this at entry=0x7f54101ddb70,
event=event at entry=RPC_TRANSPORT_MSG_RECEIVED,
data=data at entry=0x7f54000091f0) at rpc-transport.c:546 #4
0x00007f541d881666 in socket_event_poll_in
(this=this at entry=0x7f54101ddb70) at socket.c:2237 #5 0x00007f541d8842c4
in socket_event_handler (fd=fd at entry=30, idx=idx at entry=20,
data=0x7f54101ddb70, poll_in=1, poll_out=0, poll_err=0) at socket.c:2350
#6 0x00007f542a90aa4a in event_dispatch_epoll_handler
(event=0x7f540effc540, event_pool=0xd3d9a0) at event-epoll.c:575 #7
event_dispatch_epoll_worker (data=0x7f54100d0890) at event-epoll.c:678
#8 0x00007f542d0fbdc5 in start_thread () from /lib64/libpthread.so.0 #9
0x00007f542c7bc28d in clone () from /lib64/libc.so.6 Xavi
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