https://bugs.dpdk.org/show_bug.cgi?id=316
Bug ID: 316
Summary: livelock causes librte_distributor unit test to hang
Product: DPDK
Version: 19.08
Hardware: x86
OS: Linux
Status: UNCONFIRMED
Severity: normal
Priority: Normal
Component: other
Assignee: dev@dpdk.org
Reporter: msant...@redhat.com
Target Milestone: ---
Issue first encountered in Travis CI.
The meson unit test distributor_autotest randomly times out. Normally this test
finishes in less than 1/2 a second, so running to 10 seconds and timing out is
a big jump in run time.
I was able to reproduce by running:
`while sudo sh -c "echo 'distributor_autotest' | ./build/app/test/dpdk-test";
do :; done`
It runs a couple of times fine showing output and showing progress, but then at
some point after a couple of seconds it just stops - no longer getting any
output. It just sits there with no further output. I let it sit there for a
whole minute and nothing happens. So I attach gdb to try to figure out what is
happening. One thread seems to be stuck on a while loop, see
lib/librte_distributor/rte_distributor.c:310.
I looked at the assembly code (layout asm, ni) and I saw these four lines below
(which correspond to the while loop) being executed repeatedly and
indefinitely. It looks like this thread is waiting for the variable bufptr64[0]
to change state.
0xa064d0 <release+32> pause
0xa064d2 <release+34> mov 0x3840(%rdx),%rax
0xa064d9 <release+41> test $0x1,%al
0xa064db <release+43> je 0xa064d0 <release+32>
While the first thread is waiting on bufptr64[0] to change state, there is
another thread that is also stuck on another while loop on
lib/librte_distributor/rte_distributor.c:53. It seems that this thread is stuck
waiting for retptr64 to change state. Corresponding assembly being executed
indefinitely:
0xa06de0 <rte_distributor_request_pkt_v1705+592> mov 0x38c0(%r8),%rax
0xa06de7 <rte_distributor_request_pkt_v1705+599> test $0x1,%al
0xa06de9 <rte_distributor_request_pkt_v1705+601> je 0xa06bbd
<rte_distributor_request_pkt_v1705+45>
0xa06def <rte_distributor_request_pkt_v1705+607> nop
0xa06df0 <rte_distributor_request_pkt_v1705+608> pause
0xa06df2 <rte_distributor_request_pkt_v1705+610> rdtsc
0xa06df4 <rte_distributor_request_pkt_v1705+612> mov %rdx,%r10
0xa06df7 <rte_distributor_request_pkt_v1705+615> shl $0x20,%r10
0xa06dfb <rte_distributor_request_pkt_v1705+619> mov %eax,%eax
0xa06dfd <rte_distributor_request_pkt_v1705+621> or %r10,%rax
0xa06e00 <rte_distributor_request_pkt_v1705+624> lea 0x64(%rax),%r10
0xa06e04 <rte_distributor_request_pkt_v1705+628> jmp 0xa06e12
<rte_distributor_request_pkt_v1705+642>
0xa06e06 <rte_distributor_request_pkt_v1705+630> nopw %cs:0x0(%rax,%rax,1)
0xa06e10 <rte_distributor_request_pkt_v1705+640> pause
0xa06e12 <rte_distributor_request_pkt_v1705+642> rdtsc
0xa06e14 <rte_distributor_request_pkt_v1705+644> shl $0x20,%rdx
0xa06e18 <rte_distributor_request_pkt_v1705+648> mov %eax,%eax
0xa06e1a <rte_distributor_request_pkt_v1705+650> or %rdx,%rax
0xa06e1d <rte_distributor_request_pkt_v1705+653> cmp %rax,%r10
0xa06e20 <rte_distributor_request_pkt_v1705+656> ja 0xa06e10
<rte_distributor_request_pkt_v1705+640>
0xa06e22 <rte_distributor_request_pkt_v1705+658> jmp 0xa06de0
<rte_distributor_request_pkt_v1705+592>
My guess is that these threads are interdependent, so one thread is waiting for
the other thread to change the state of the control variable. I can't say for
sure if this is what is happening or why the these variables don't change
state, so I would like ask someone who is more familiar with this particular
code to take a look
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