apache hangs frequently with semop

Posted by PiTheNumber on Server Fault See other posts from Server Fault or by PiTheNumber
Published on 2012-11-10T09:17:29Z Indexed on 2012/11/10 11:06 UTC
Read the original article Hit count: 357

Filed under:

apache2

|

centos

|

hangs

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?

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