Hi,

Having new LTS 2.0 available we gave it a shot and we started
experiencing segfaults like this:

Tue Jan 28 16:25:52 2014 - Respawned uWSGI worker 2 (new pid: 16845)
Tue Jan 28 16:25:52 2014 - worker 3 killed successfully (pid: 16821)
Tue Jan 28 16:25:52 2014 - uwsgi::postfork handler: Just forked worker 16845
Tue Jan 28 16:25:52 2014 - Respawned uWSGI worker 3 (new pid: 16847)
Tue Jan 28 16:25:52 2014 - uwsgi::postfork handler: Just forked worker 16847
Tue Jan 28 16:25:52 2014 - uwsgi::postfork handler: Ran 2 post-fork action(s) 
for 16845 in 81 ms (child_init in 81 ms, record_start_time in 0 ms)
Tue Jan 28 16:25:52 2014 - uwsgi::postfork handler: Ran 2 post-fork action(s) 
for 16847 in 67 ms (child_init in 67 ms, record_start_time in 0 ms)
Tue Jan 28 16:25:53 2014 - !!! uWSGI process 16817 got Segmentation Fault !!!
Tue Jan 28 16:25:53 2014 - *** backtrace of 16817 ***
/usr/sbin/uwsgi(uwsgi_backtrace+0x29) [0x45a8a9]
/usr/sbin/uwsgi(uwsgi_segfault+0x21) [0x45aa31]
/lib64/libc.so.6 [0x3efde302f0]
/usr/sbin/uwsgi(uwsgi_lock_ipcsem+0x1a) [0x44599a]
/usr/lib64/uwsgi/cheaper_busyness_plugin.so(cheaper_busyness_algo+0x24c) 
[0x2b48f11895bc]
/usr/sbin/uwsgi(uwsgi_calc_cheaper+0x202) [0x428c82]
/usr/sbin/uwsgi(master_loop+0x11fe) [0x42562e]
/usr/sbin/uwsgi(uwsgi_run+0x250) [0x457db0]
/lib64/libc.so.6(__libc_start_main+0xf4) [0x3efde1d994]
/usr/sbin/uwsgi [0x413399]
*** end of backtrace ***
Tue Jan 28 16:25:53 2014 - found ipcsem mapped to alive pid 16822. skipping 
ipcsem removal. 
Tue Jan 28 16:25:53 2014 - uWSGI worker 4 screams: UAAAAAAH my master 
disconnected: i will kill myself !!!
Tue Jan 28 16:25:53 2014 - uWSGI worker 6 screams: UAAAAAAH my master 
disconnected: i will kill myself !!!
...

This seems to be related to busyness plugin as disabling it works around
the problem. Relevant configuration (we run PSGI app):

cheaper = 12
cheaper-initial = 24
processes = 48
cheaper-algo = busyness
cheaper-overload = 5
cheaper-step = 1
cheaper-busyness-multiplier = 2
cheaper-busyness-min = 60
cheaper-busyness-max = 80
cheaper-busyness-backlog-alert = 1
cheaper-busyness-backlog-step = 3
cheaper-busyness-backlog-multiplier = 1

thunder-lock = true
lock-engine = ipcsem
ftok = /etc/uwsgi/ftok

This configuration works just fine with 1.4.10 and *MOST LIKELY* 1.9.20
(we get different error which was identified as bug in our code
which just worked with 1.4.x and doesn't with 1.9.20)

Marcin
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