Segmentation fault

• uvloop version:
  0.16.0
• Python version:
  Python 3.7.10
• Platform:
  Amazon Linux release 2 (Karoo)

It happens couple of times a day sometimes. And than does not happen for weeks:

Thread 2 "python3.7" received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7fffe71b3700 (LWP 31714)]
0x0000000000000000 in ?? ()
Missing separate debuginfos, use: debuginfo-install python3-3.7.10-1.amzn2.0.1.x86_64
(gdb) bt
#0  0x0000000000000000 in ?? ()
#1  0x00007fffe97b2a5b in uv__read (stream=stream@entry=0x7fffe01bbe40) at src/unix/stream.c:1211
#2  0x00007fffe97b2f58 in uv__stream_io (loop=<optimized out>, w=0x7fffe01bbec8, events=1) at src/unix/stream.c:1316
#3  0x00007fffe97b9e75 in uv.io_poll () at src/unix/epoll.c:374
#4  0x00007fffe97ac684 in uv_run (loop=0x9982e0, mode=mode@entry=UV_RUN_DEFAULT) at src/unix/core.c:389
#5  0x00007fffe975e1f0 in __pyx_f_6uvloop_4loop_4Loop___run (__pyx_v_self=0xa19e70, __pyx_v_mode=UV_RUN_DEFAULT) at uvloop/loop.c:14642
#6  0x00007fffe976548d in __pyx_f_6uvloop_4loop_4Loop__run (__pyx_v_self=0xa19e70, __pyx_v_mode=UV_RUN_DEFAULT) at uvloop/loop.c:15030
#7  0x00007fffe96ebbc8 in __pyx_pf_6uvloop_4loop_4Loop_24run_forever (__pyx_v_self=0xa19e70) at uvloop/loop.c:27698
#8  __pyx_pw_6uvloop_4loop_4Loop_25run_forever (__pyx_v_self=0xa19e70, unused=<optimized out>) at uvloop/loop.c:27519
#9  0x00007ffff79d9db0 in _PyMethodDef_RawFastCallKeywords () from /lib64/libpython3.7m.so.1.0
#10 0x00007ffff79f37ed in _PyMethodDescr_FastCallKeywords () from /lib64/libpython3.7m.so.1.0
#11 0x00007ffff7a37cfb in _PyEval_EvalFrameDefault () from /lib64/libpython3.7m.so.1.0
#12 0x00007ffff79cce66 in _PyFunction_FastCallKeywords () from /lib64/libpython3.7m.so.1.0
#13 0x00007ffff7a3326f in _PyEval_EvalFrameDefault () from /lib64/libpython3.7m.so.1.0
#14 0x00007ffff79cce66 in _PyFunction_FastCallKeywords () from /lib64/libpython3.7m.so.1.0
#15 0x00007ffff7a3326f in _PyEval_EvalFrameDefault () from /lib64/libpython3.7m.so.1.0
#16 0x00007ffff7995757 in _PyFunction_FastCallDict () from /lib64/libpython3.7m.so.1.0
#17 0x00007ffff79a2711 in _PyObject_Call_Prepend () from /lib64/libpython3.7m.so.1.0
#18 0x00007ffff7995baa in PyObject_Call () from /lib64/libpython3.7m.so.1.0
#19 0x00007ffff7aa0b43 in t_bootstrap () from /lib64/libpython3.7m.so.1.0
#20 0x00007ffff7a4a147 in pythread_wrapper () from /lib64/libpython3.7m.so.1.0
#21 0x00007ffff741744b in start_thread () from /lib64/libpthread.so.0
#22 0x00007ffff6a0b40f in clone () from /lib64/libc.so.6

My app is using uvloop + aiohttp to continiously poll certain websites with high frequency. There are couple of threads which a sending tasks to a single thread where uvloop loop runs.

Both processes where this reproduces run at -17 and -20 niceness. There are some other processes with niceness around -10,-12 where it never reproduced. So maybe somehow related.

Start with the supplied GDB backtrace and inspect uvloop/loop.c around Loop.__run and Loop._run, then compare it with libuv's src/unix/stream.c and src/unix/epoll.c. Reproduce the intermittent SIGSEGV under the reported Python, uvloop, Amazon Linux, threading, and niceness conditions; done means the crash cause is identified and addressed.