Description:
------------
I occasionally experience apache2 child crashes, Couldn't reproduce it manually... Got lots of coredumps, but it seems they come from a different place each time.
Attached are backtraces of the most popular ones.
Machine is Ubuntu 14, libapache2-mod-php5.6, php 5.6.33+3, Apache/2.4.7,  installed from ondrej ppa.

Actual result:
--------------
(gdb) bt full
#0  0x00007f9e85698f13 in get_default_charset () at /build/php5.6-I6I9am/php5.6-5.6.33/ext/standard/html.c:90
No locals.
#1  0x00007f9e8569b735 in php_html_entities (ht=<optimized out>, return_value=0x7f9e8d0ea070, all=0, return_value_used=<optimized out>, this_ptr=<optimized out>, return_value_ptr=<optimized out>)
    at /build/php5.6-I6I9am/php5.6-5.6.33/ext/standard/html.c:1464
        str = 0x7f9e8d0ea910 "Status changed to CREATE (5)"
        hint_charset = 0x0
        str_len = 28
        hint_charset_len = 0
        new_len = 140318948106352
        flags = 2
        replaced = <optimized out>
        double_encode = 1 '\001'
#2  0x00007f9e85733b1b in dtrace_execute_internal (execute_data_ptr=<optimized out>, fci=<optimized out>, return_value_used=<optimized out>) at /build/php5.6-I6I9am/php5.6-5.6.33/Zend/zend_dtrace.c:97
        lineno = <optimized out>
        filename = <optimized out>
#3  0x00007f9e857e9b54 in zend_do_fcall_common_helper_SPEC (execute_data=<optimized out>) at /build/php5.6-I6I9am/php5.6-5.6.33/Zend/zend_vm_execute.h:560
        ret = 0x7f9e8986aa00
        opline = <optimized out>
        should_change_scope = <optimized out>
        fbc = 0x7f9e8a6303d0
        num_args = <optimized out>
#4  0x00007f9e8577f0b8 in execute_ex (execute_data=0x7f9e8986aa40) at /build/php5.6-I6I9am/php5.6-5.6.33/Zend/zend_vm_execute.h:363
        ret = <optimized out>
        original_in_execution = 1 '\001'
#5  0x00007f9e85733a19 in dtrace_execute_ex (execute_data=<optimized out>) at /build/php5.6-I6I9am/php5.6-5.6.33/Zend/zend_dtrace.c:73
        lineno = <optimized out>
        scope = 0x0
        filename = <optimized out>
        funcname = <optimized out>
        classname = <optimized out>
#6  0x00007f9e7544c74e in nr_php_execute_enabled () at /home/hudson/slave-workspace/workspace/php-release-agent/label/centos5-64-nrcamp/agent/php_execute.c:1191
No locals.
#7  0x00007f9e7544ce32 in nr_php_execute () at /home/hudson/slave-workspace/workspace/php-release-agent/label/centos5-64-nrcamp/agent/php_execute.c:1301
No locals.
#8  0x00007f9e857ea077 in zend_do_fcall_common_helper_SPEC (execute_data=<optimized out>) at /build/php5.6-I6I9am/php5.6-5.6.33/Zend/zend_vm_execute.h:592
        ret = 0x7f9e8986a848
        opline = 0x7f9e71250a08
        should_change_scope = <optimized out>
        fbc = 0x7f9e8d0e8750
        num_args = <optimized out>
#9  0x00007f9e8577f0b8 in execute_ex (execute_data=0x7f9e8986a868) at /build/php5.6-I6I9am/php5.6-5.6.33/Zend/zend_vm_execute.h:363
        ret = <optimized out>
        original_in_execution = 1 '\001'
#10 0x00007f9e85733a19 in dtrace_execute_ex (execute_data=<optimized out>) at /build/php5.6-I6I9am/php5.6-5.6.33/Zend/zend_dtrace.c:73
---Type <return> to continue, or q <return> to quit---
        lineno = <optimized out>
        scope = 0x0
        filename = <optimized out>
        funcname = <optimized out>
        classname = <optimized out>
#11 0x00007f9e7544c74e in nr_php_execute_enabled () at /home/hudson/slave-workspace/workspace/php-release-agent/label/centos5-64-nrcamp/agent/php_execute.c:1191
No locals.
#12 0x00007f9e7544ce32 in nr_php_execute () at /home/hudson/slave-workspace/workspace/php-release-agent/label/centos5-64-nrcamp/agent/php_execute.c:1301
No locals.
#13 0x00007f9e8573574f in zend_call_function (fci=fci@entry=0x7ffff6617a90, fci_cache=<optimized out>, fci_cache@entry=0x7ffff6617a60) at /build/php5.6-I6I9am/php5.6-5.6.33/Zend/zend_execute_API.c:831
        current_opline_before_exception = 0x7f9e723b6710
        i = <optimized out>
        original_return_value = 0x0
        calling_symbol_table = 0x0
        original_op_array = 0x7f9e8ad8a560
        original_opline_ptr = 0x7f9e8986a6a8
        current_scope = 0x7f9e8ad7e3b0
        current_called_scope = 0x7f9e8ad7d128
        calling_scope = <optimized out>
        called_scope = 0x7f9e8cf258f0
        current_this = 0x7f9e8cf0e108
        execute_data = {opline = 0x0, function_state = {function = 0x7f9e8cf26068, arguments = 0x7f9e8986a7e0}, op_array = 0x0, object = 0x7f9e8cf3ffb0, symbol_table = 0x0,
          prev_execute_data = 0x7f9e8986a6a8, old_error_reporting = 0x0, nested = 0 '\000', original_return_value = 0x0, current_scope = 0x7f9e8ad7e3b0, current_called_scope = 0x7f9e8ad7d128,
          current_this = 0x7f9e8cf0e108, fast_ret = 0x0, delayed_exception = 0x0, call_slots = 0x7f9e8986a790, call = 0x7f9e8986a790}
        fci_cache_local = {initialized = 4 '\004', function_handler = 0x7f9e8574e798 <zend_parse_parameters+152>, calling_scope = 0x7f9e85b32f00 <executor_globals+576>, called_scope = 0x3000000028,
          object_ptr = 0x7ffff6617a50}
#14 0x00007f9e85682472 in zif_call_user_func_array (ht=<optimized out>, return_value=0x7f9e8cfe4710, return_value_ptr=<optimized out>, this_ptr=<optimized out>, return_value_used=<optimized out>)
    at /build/php5.6-I6I9am/php5.6-5.6.33/ext/standard/basic_functions.c:4790
        params = 0x7f9e8cfe4688
        retval_ptr = 0x0
        fci = {size = 72, function_table = 0x7f9e8cf25918, function_name = 0x7f9e8cf42750, symbol_table = 0x0, retval_ptr_ptr = 0x7ffff6617a58, param_count = 3, params = 0x7f9e8cfddc18,
          object_ptr = 0x7f9e8cf3ffb0, no_separation = 1 '\001'}
        fci_cache = {initialized = 1 '\001', function_handler = 0x7f9e8cf26068, calling_scope = 0x7f9e8cf258f0, called_scope = 0x7f9e8cf258f0, object_ptr = 0x7f9e8cf3ffb0}
#15 0x00007f9e85733b1b in dtrace_execute_internal (execute_data_ptr=<optimized out>, fci=<optimized out>, return_value_used=<optimized out>) at /build/php5.6-I6I9am/php5.6-5.6.33/Zend/zend_dtrace.c:97
        lineno = <optimized out>
        filename = <optimized out>
#16 0x00007f9e857e9b54 in zend_do_fcall_common_helper_SPEC (execute_data=<optimized out>) at /build/php5.6-I6I9am/php5.6-5.6.33/Zend/zend_vm_execute.h:560
        ret = 0x7f9e8986a688
        opline = <optimized out>
        should_change_scope = <optimized out>
        fbc = 0x7f9e8a641380
        num_args = <optimized out>
#17 0x00007f9e8577f0b8 in execute_ex (execute_data=0x7f9e8986a6a8) at /build/php5.6-I6I9am/php5.6-5.6.33/Zend/zend_vm_execute.h:363
        ret = <optimized out>
---Type <return> to continue, or q <return> to quit---
        original_in_execution = 1 '\001'
#18 0x00007f9e85733a19 in dtrace_execute_ex (execute_data=<optimized out>) at /build/php5.6-I6I9am/php5.6-5.6.33/Zend/zend_dtrace.c:73
        lineno = <optimized out>
        scope = 0x0
        filename = <optimized out>
        funcname = <optimized out>
        classname = <optimized out>
#19 0x00007f9e7544c74e in nr_php_execute_enabled () at /home/hudson/slave-workspace/workspace/php-release-agent/label/centos5-64-nrcamp/agent/php_execute.c:1191
No locals.
#20 0x00007f9e7544ce32 in nr_php_execute () at /home/hudson/slave-workspace/workspace/php-release-agent/label/centos5-64-nrcamp/agent/php_execute.c:1301
No locals.
#21 0x00007f9e857ea077 in zend_do_fcall_common_helper_SPEC (execute_data=<optimized out>) at /build/php5.6-I6I9am/php5.6-5.6.33/Zend/zend_vm_execute.h:592
        ret = 0x7f9e8986a538
        opline = 0x7f9e6ff90068
        should_change_scope = <optimized out>
        fbc = 0x7f9e8ad8a560
        num_args = <optimized out>
#22 0x00007f9e8577f0b8 in execute_ex (execute_data=0x7f9e8986a558) at /build/php5.6-I6I9am/php5.6-5.6.33/Zend/zend_vm_execute.h:363
        ret = <optimized out>
        original_in_execution = 1 '\001'
#23 0x00007f9e85733a19 in dtrace_execute_ex (execute_data=<optimized out>) at /build/php5.6-I6I9am/php5.6-5.6.33/Zend/zend_dtrace.c:73
        lineno = <optimized out>
        scope = 0x0
        filename = <optimized out>
        funcname = <optimized out>
        classname = <optimized out>
#24 0x00007f9e7544c74e in nr_php_execute_enabled () at /home/hudson/slave-workspace/workspace/php-release-agent/label/centos5-64-nrcamp/agent/php_execute.c:1191
No locals.
#25 0x00007f9e7544ce32 in nr_php_execute () at /home/hudson/slave-workspace/workspace/php-release-agent/label/centos5-64-nrcamp/agent/php_execute.c:1301
No locals.
#26 0x00007f9e857ea077 in zend_do_fcall_common_helper_SPEC (execute_data=<optimized out>) at /build/php5.6-I6I9am/php5.6-5.6.33/Zend/zend_vm_execute.h:592
        ret = 0x7f9e8986a400
        opline = 0x7f9e6f9613f8
        should_change_scope = <optimized out>
        fbc = 0x7f9e8ad7e2a8
        num_args = <optimized out>
#27 0x00007f9e8577f0b8 in execute_ex (execute_data=0x7f9e8986a420) at /build/php5.6-I6I9am/php5.6-5.6.33/Zend/zend_vm_execute.h:363
        ret = <optimized out>
        original_in_execution = 1 '\001'
#28 0x00007f9e85733a19 in dtrace_execute_ex (execute_data=<optimized out>) at /build/php5.6-I6I9am/php5.6-5.6.33/Zend/zend_dtrace.c:73
        lineno = <optimized out>
        scope = 0x0
        filename = <optimized out>
        funcname = <optimized out>
---Type <return> to continue, or q <return> to quit---
        classname = <optimized out>
#29 0x00007f9e7544ca92 in nr_php_execute_file () at /home/hudson/slave-workspace/workspace/php-release-agent/label/centos5-64-nrcamp/agent/php_execute.c:856
No locals.
#30 nr_php_execute_enabled () at /home/hudson/slave-workspace/workspace/php-release-agent/label/centos5-64-nrcamp/agent/php_execute.c:1073
No locals.
#31 0x00007f9e7544ce32 in nr_php_execute () at /home/hudson/slave-workspace/workspace/php-release-agent/label/centos5-64-nrcamp/agent/php_execute.c:1301
No locals.
#32 0x00007f9e857e93cf in ZEND_INCLUDE_OR_EVAL_SPEC_CONST_HANDLER (execute_data=0x7f9e8986a358) at /build/php5.6-I6I9am/php5.6-5.6.33/Zend/zend_vm_execute.h:3026
        opline = 0x7f9e6f960460
        new_op_array = 0x7f9e898a0e88
        inc_filename = 0x7f9e6f960410
        tmp_inc_filename = 0x0
        failure_retval = 0 '\000'
#33 0x00007f9e8577f0b8 in execute_ex (execute_data=0x7f9e8986a358) at /build/php5.6-I6I9am/php5.6-5.6.33/Zend/zend_vm_execute.h:363
        ret = <optimized out>
        original_in_execution = 0 '\000'
#34 0x00007f9e85733a19 in dtrace_execute_ex (execute_data=<optimized out>) at /build/php5.6-I6I9am/php5.6-5.6.33/Zend/zend_dtrace.c:73
        lineno = <optimized out>
        scope = 0x0
        filename = <optimized out>
        funcname = <optimized out>
        classname = <optimized out>
#35 0x00007f9e7544ca92 in nr_php_execute_file () at /home/hudson/slave-workspace/workspace/php-release-agent/label/centos5-64-nrcamp/agent/php_execute.c:856
No locals.
#36 nr_php_execute_enabled () at /home/hudson/slave-workspace/workspace/php-release-agent/label/centos5-64-nrcamp/agent/php_execute.c:1073
No locals.
#37 0x00007f9e7544ce32 in nr_php_execute () at /home/hudson/slave-workspace/workspace/php-release-agent/label/centos5-64-nrcamp/agent/php_execute.c:1301
No locals.
#38 0x00007f9e85745e50 in zend_execute_scripts (type=type@entry=8, retval=retval@entry=0x0, file_count=file_count@entry=3) at /build/php5.6-I6I9am/php5.6-5.6.33/Zend/zend.c:1341
        files = {{gp_offset = 40, fp_offset = 32670, overflow_arg_area = 0x7ffff66185c0, reg_save_area = 0x7ffff6618550}}
        i = 1
        file_handle = 0x7ffff661a840
        orig_op_array = 0x0
        orig_retval_ptr_ptr = 0x0
        orig_interactive = 0
#39 0x00007f9e856e3832 in php_execute_script (primary_file=primary_file@entry=0x7ffff661a840) at /build/php5.6-I6I9am/php5.6-5.6.33/main/main.c:2613
        realfile = "\034\000\000\000\000\000\000\000\005", '\000' <repeats 11 times>, "\236\177\000\000\000\177ኞ\177\000\000u<f\240\062\376\035\000\071\277q\205\236\177\000\000\177\003\000\000\000\000\000\000\240\000\000\000\000\000\000\000\200\226a\366\377\177\000\000\300\226a\366\377\177\000\000\000\227a\366\377\177\000\000\002", '\000' <repeats 15 times>, "\373\377\377\377f\000\000\000\001\000\000\000\000\000\000\000\071\277q\205\236\177\000\000p\217댞\177\000\000\200\236a\366\377\177\000\000\200\236a\366\377\177\000\000p\236a\366\377\177\000\000i\017\206\210\236\177\000\000VlKu\236\177\000\000\240\236a\366\377\177\000\000\220\236a\366\377\177\000\000i\017\206\210\236\177\000\000[lKu"...
        __orig_bailout = 0x7ffff661a8c0
        __bailout = {{__jmpbuf = {140318887902472, -8779197948997737314, 140318887902472, 140318890020800, 0, 140318887989904, -8779197949643660130, -8725473701159967586}, __mask_was_saved = 0,
            __saved_mask = {__val = {1132913822, 9223372032559808614, 0, 7, 140737326978624, 4294967296, 140737326978632, 140737326979568, 0, 140737326978592, 140318873309515, 0, 140737326980736,
                140737326978602, 1, 4579595891102449657}}}}
---Type <return> to continue, or q <return> to quit---
        prepend_file_p = <optimized out>
        append_file_p = 0x0
        prepend_file = {type = ZEND_HANDLE_FILENAME, filename = 0x0, opened_path = 0x0, handle = {fd = 0, fp = 0x0, stream = {handle = 0x0, isatty = 0, mmap = {len = 0, pos = 0, map = 0x0, buf = 0x0,
                old_handle = 0x0, old_closer = 0x0}, reader = 0x0, fsizer = 0x0, closer = 0x0}}, free_filename = 0 '\000'}
        append_file = {type = ZEND_HANDLE_FILENAME, filename = 0x0, opened_path = 0x0, handle = {fd = 0, fp = 0x0, stream = {handle = 0x0, isatty = 0, mmap = {len = 0, pos = 0, map = 0x0, buf = 0x0,
                old_handle = 0x0, old_closer = 0x0}, reader = 0x0, fsizer = 0x0, closer = 0x0}}, free_filename = 0 '\000'}
        old_cwd = 0x7ffff66185d0 "/"
        retval = 0
#40 0x00007f9e857eb6e2 in php_handler (r=<optimized out>) at /build/php5.6-I6I9am/php5.6-5.6.33/sapi/apache2handler/sapi_apache2.c:667
        zfd = {type = ZEND_HANDLE_FILENAME, filename = 0x7f9e89786ba8 "/home/blazemeter/vol/www/a.blazemeter.com/public/api.php", opened_path = 0x0, handle = {fd = -161371780, fp = 0x7ffff661a97c,
            stream = {handle = 0x7ffff661a97c, isatty = -1988596824, mmap = {len = 140318797637872, pos = 140318887932256, map = 0x7f9e00000000, buf = 0x7f9e898b4148 "", old_handle = 0x7f9e898b85e0,
                old_closer = 0x7f9e898b85e0}, reader = 0x7f9e89787028, fsizer = 0x7f9e8977fd08, closer = 0x7f9e89795290}}, free_filename = 0 '\000'}
        __orig_bailout = 0x0
        __bailout = {{__jmpbuf = {140318887902472, 8779179482153149598, 140318887902472, 140318890020800, 0, 140318887989904, -8779197948999834466, -8725473842931637090}, __mask_was_saved = 0,
            __saved_mask = {__val = {140318887902472, 0, 140318887902896, 140318889605128, 140318889276184, 140318887932328, 140318887936160, 140318890020800, 0, 140318887989904, 140318833196195,
                140318890020800, 0, 140318887932328, 140318887902472, 140318889171024}}}}
        ctx = 0x7f9e89787210
        conf = <optimized out>
        brigade = 0x7f9e89787f50
        bucket = <optimized out>
        rv = <optimized out>
        parent_req = 0x0
#41 0x00007f9e8973f120 in ap_run_handler ()
No symbol table info available.
#42 0x00007f9e8973f669 in ap_invoke_handler ()
No symbol table info available.
#43 0x00007f9e897546fc in ap_internal_redirect ()
No symbol table info available.
#44 0x00007f9e84162cfc in ?? () from /usr/lib/apache2/modules/mod_rewrite.so
No symbol table info available.
#45 0x00007f9e8973f120 in ap_run_handler ()
No symbol table info available.
#46 0x00007f9e8973f669 in ap_invoke_handler ()
No symbol table info available.
#47 0x00007f9e89754c3a in ap_process_async_request ()
No symbol table info available.
#48 0x00007f9e89754f14 in ap_process_request ()
No symbol table info available.
#49 0x00007f9e897519b2 in ?? ()
No symbol table info available.
#50 0x00007f9e89748790 in ap_run_process_connection ()
No symbol table info available.
#51 0x00007f9e85d42767 in ?? () from /usr/lib/apache2/modules/mod_mpm_prefork.so
No symbol table info available.
---Type <return> to continue, or q <return> to quit---
#52 0x00007f9e85d429a6 in ?? () from /usr/lib/apache2/modules/mod_mpm_prefork.so
No symbol table info available.
#53 0x00007f9e85d4360e in ?? () from /usr/lib/apache2/modules/mod_mpm_prefork.so
No symbol table info available.
#54 0x00007f9e8972428e in ap_run_mpm ()
No symbol table info available.
#55 0x00007f9e8971d2e6 in main ()
No symbol table info available.






=========================================================





(gdb) bt full
#0  php_apache_sapi_header_handler (sapi_header=<optimized out>, op=SAPI_HEADER_ADD, sapi_headers=<optimized out>) at /build/php5.6-I6I9am/php5.6-5.6.33/sapi/apache2handler/sapi_apache2.c:124
        ctx = 0x0
        val = 0x7f9e8cc2b986 "text/html; charset=UTF-8"
        ptr = 0x7f9e8cc2b984 ""
#1  0x00007f9e856ea1e3 in sapi_header_add_op (op=SAPI_HEADER_ADD, sapi_header=0x7ffff661a500) at /build/php5.6-I6I9am/php5.6-5.6.33/main/SAPI.c:658
No locals.
#2  0x00007f9e856eb69f in sapi_send_headers () at /build/php5.6-I6I9am/php5.6-5.6.33/main/SAPI.c:879
        default_header = {header = 0x7f9e8cc2b978 "Content-type", header_len = 38}
        len = 24
        retval = <optimized out>
        ret = -1
#3  0x00007f9e85698359 in php_header () at /build/php5.6-I6I9am/php5.6-5.6.33/ext/standard/head.c:68
No locals.
#4  0x00007f9e856f37e4 in php_output_header () at /build/php5.6-I6I9am/php5.6-5.6.33/main/output.c:122
No locals.
#5  0x00007f9e856f4575 in php_output_deactivate () at /build/php5.6-I6I9am/php5.6-5.6.33/main/output.c:176
        handler = 0x0
#6  0x00007f9e856e25a5 in php_request_shutdown (dummy=dummy@entry=0x0) at /build/php5.6-I6I9am/php5.6-5.6.33/main/main.c:1873
        __orig_bailout = 0x0
        __bailout = {{__jmpbuf = {140318824672448, 8779161889967367326, 140318888473168, 140318890020800, 0, 140318888575632, -8779197948668484450, -8725473701841673058}, __mask_was_saved = 0,
            __saved_mask = {__val = {140318888499856, 9, 1297040479, 140318888499856, 140318888476256, 13, 140318877984231, 57, 140318888476576, 140318821580631, 140318877995302, 55834574849,
                140318888473168, 140318824671136, 140318888473168, 2}}}}
        report_memleaks = 1 '\001'
#7  0x00007f9e857eb5ff in php_apache_request_dtor (r=<optimized out>) at /build/php5.6-I6I9am/php5.6-5.6.33/sapi/apache2handler/sapi_apache2.c:507
No locals.
#8  php_handler (r=<optimized out>) at /build/php5.6-I6I9am/php5.6-5.6.33/sapi/apache2handler/sapi_apache2.c:679
        ctx = 0x7f9e8980c760
        conf = <optimized out>
        brigade = 0x7f9e89811768
        bucket = <optimized out>
        rv = <optimized out>
        parent_req = 0x0
#9  0x00007f9e8973f120 in ap_run_handler ()
No symbol table info available.
#10 0x00007f9e8973f669 in ap_invoke_handler ()
No symbol table info available.
#11 0x00007f9e897546fc in ap_internal_redirect ()
No symbol table info available.
#12 0x00007f9e84162cfc in ?? () from /usr/lib/apache2/modules/mod_rewrite.so
No symbol table info available.
#13 0x00007f9e8973f120 in ap_run_handler ()
No symbol table info available.
#14 0x00007f9e8973f669 in ap_invoke_handler ()
No symbol table info available.
---Type <return> to continue, or q <return> to quit---
#15 0x00007f9e89754c3a in ap_process_async_request ()
No symbol table info available.
#16 0x00007f9e89754f14 in ap_process_request ()
No symbol table info available.
#17 0x00007f9e897519b2 in ?? ()
No symbol table info available.
#18 0x00007f9e89748790 in ap_run_process_connection ()
No symbol table info available.
#19 0x00007f9e85d42767 in ?? () from /usr/lib/apache2/modules/mod_mpm_prefork.so
No symbol table info available.
#20 0x00007f9e85d429a6 in ?? () from /usr/lib/apache2/modules/mod_mpm_prefork.so
No symbol table info available.
#21 0x00007f9e85d4360e in ?? () from /usr/lib/apache2/modules/mod_mpm_prefork.so
No symbol table info available.
#22 0x00007f9e8972428e in ap_run_mpm ()
No symbol table info available.
#23 0x00007f9e8971d2e6 in main ()
No symbol table info available.