更新：我注意到类似问题，也许相关。但我将 MPM 模块更改为 MPM 事件，如此 GDB BT 中所述：
#0 0x00007fc74ea90df4 in read () from target:/lib64/libpthread.so.0
#1 0x000055df44ca24cb in ap_mpm_podx_check ()
#2 0x00007fc74e1f4f57 in ?? () from target:/etc/httpd/modules/mod_mpm_event.so
#3 0x00007fc74e1f528a in ?? () from target:/etc/httpd/modules/mod_mpm_event.so
#4 0x00007fc74e1f531b in ?? () from target:/etc/httpd/modules/mod_mpm_event.so
#5 0x00007fc74e1f6017 in ?? () from target:/etc/httpd/modules/mod_mpm_event.so
#6 0x000055df44c76bde in ap_run_mpm ()
#7 0x000055df44c6f2d3 in main ()
升级到 Fedora 29 后，这种情况开始发生。首先，MySQL 开始使用大量 CPU，但其他主题然后，Apache/httpd 开始真正消耗 CPU。
top - 16:58:34 up 1 day, 5:14, 2 users, load average: 22.06, 21.55, 21.13
Tasks: 273 total, 1 running, 272 sleeping, 0 stopped, 0 zombie
%Cpu(s): 12.5 us, 1.0 sy, 8.0 ni, 76.8 id, 1.6 wa, 0.1 hi, 0.0 si, 0.0 st
MiB Mem : 7968.8 total, 217.8 free, 1812.1 used, 5938.9 buff/cache
MiB Swap: 8000.0 total, 7547.9 free, 452.1 used. 5843.4 avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
12985 apache 20 0 2339912 17908 10748 S 99.3 0.2 3:42.00 /usr/sbin/httpd
我尝试在进程 ID 上运行gdb并bt得到很多Missing separate debuginfo for target，但它结束于：
0x00007f3e4a31cdf4 in read () from target:/lib64/libpthread.so.0
(gdb) bt
#0 0x00007f3e4a31cdf4 in read () from target:/lib64/libpthread.so.0
#1 0x00005640ecf6c4cb in ap_mpm_podx_check ()
#2 0x00007f3e49a128de in ?? () from target:/etc/httpd/modules/mod_mpm_worker.so
#3 0x00007f3e49a12c89 in ?? () from target:/etc/httpd/modules/mod_mpm_worker.so
#4 0x00007f3e49a12d1b in ?? () from target:/etc/httpd/modules/mod_mpm_worker.so
#5 0x00007f3e49a13b7f in ?? () from target:/etc/httpd/modules/mod_mpm_worker.so
#6 0x00005640ecf40bde in ap_run_mpm ()
#7 0x00005640ecf392d3 in main ()
(gdb) quit
A debugging session is active.
对进程号的 strace 挂在strace: Process 12985 attached read(8,
并且 Squirrelmail/webmail 超时504 Gateway Timeout。Apache 错误日志中的唯一错误似乎不相关：
[Fri Jan 04 16:07:01.341027 2019] [proxy_fcgi:error] [pid 12985:tid 139904902215424] [client 201.141.38.249:51260] AH01071: Got error 'Primary script unknown\n'
<standard input>:13515: warning [p 113, 7.8i]: can't break line
<standard input>:13668: warning [p 115, 0.2i]: can't break line
<standard input>:686: warning [p 7, 4.5i, div `3tbd0,0', 0.2i]: can't break line
<standard input>:692: warning [p 7, 4.5i, div `3tbd0,3', 0.0i]: can't break line
<standard input>:694: warning [p 7, 4.5i, div `3tbd0,4', 0.0i]: can't break line
<standard input>:696: warning [p 7, 4.5i, div `3tbd0,5', 0.0i]: can't break line
<standard input>:700: warning [p 7, 4.5i, div `3tbd0,7', 0.0i]: can't break line
warning: file `<standard input>', around line 691:
table wider than line width
<standard input>:1459: warning [p 11, 5.0i]: can't break line
<standard input>:40: warning [p 1, 2.5i]: can't break line
<standard input>:85: warning: can't find special character `u4F60'
<standard input>:85: warning: can't find special character `u597D'
<standard input>:347: warning [p 4, 7.8i, div `3tbd1,0', 0.0i]: can't break line
<standard input>:360: warning [p 4, 7.8i, div `3tbd4,0', 0.0i]: can't break line
<standard input>:380: warning [p 4, 7.8i, div `3tbd8,0', 0.0i]: can't break line
<standard input>:424: warning [p 5, 0.2i, div `3tbd1,0', 0.0i]: can't break line
<standard input>:424: warning [p 5, 0.2i, div `3tbd1,0', 0.3i]: can't break line
<standard input>:485: warning [p 5, 0.2i, div `3tbd14,0', 0.0i]: can't break line
<standard input>:1379: warning [p 13, 12.0i, div `3tbd10,1', 0.0i]: can't break line
<standard input>:1384: warning [p 13, 12.0i, div `3tbd11,0', 0.0i]: can't break line
<standard input>:1903: warning [p 15, 20.8i]: can't break line
[Fri Jan 04 16:59:13.393915 2019] [proxy_fcgi:error] [pid 12981:tid 139904482776832] [client 119.185.41.131:54918] AH01071: Got error 'Primary script unknown\n',
这不是一个特别繁忙的服务器，并且access_logs没有被填满，所以我不认为这是一个 DOS。