apache hangs frequently with semop
- by PiTheNumber
My Apache hangs frequently with multiple threads. Each thread get stucked for hours. Backtrace looks like this:
(gdb) backtrace
#0 0x00002af60c22b2d7 in semop () from /lib64/libc.so.6
#1 0x00002af60bbf612c in ?? () from /usr/lib64/libapr-1.so.0
#2 0x000055555559e614 in ?? () from /usr/sbin/httpd2-prefork
#3 0x000055555559e9ea in ?? () from /usr/sbin/httpd2-prefork
#4 0x000055555559f25d in ap_mpm_run () from /usr/sbin/httpd2-prefork
#5 0x000055555557a080 in main () from /usr/sbin/httpd2-prefork
With strace I see they are waiting for a pipe that is connection all Apache threads.
strace -p 3069
....
read(7, 0x7fff16a04df7, 1) = -1 EAGAIN (Resource temporarily unavailable)
semop(286162952, 0x2af60bd07dc0, 1 <unfinished ...>
What is Apache doing here?
How can I figure out what is causing this?