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POThin server process hanging at 100% CPU in what appears to be a regex loop. Where can I get more information to debug?
 

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  1. POThin server process hanging at 100% CPU in what appears to be a regex loop. Where can I get more information to debug?
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    <p>I have a gdb backtrace on it that yields this:</p> <pre><code>#0 match_at (reg=0xcce4a00, str=0xd47b101 "206193045.1297252703.66.40.utmcsr=sendmail|utmccn=52%%20off|utmcmd=email|utmctr=View%20this|utmcct=52%%20off", end=0xd47b1a6 "", sstart=0xd47b101 "206193045.1297252703.66.40.utmcsr=sendmail|utmccn=52%%20off|utmcmd=email|utmctr=View%20this|utmcct=52%%20off", sprev=0xd47b131 "52%%20off|utmcmd=email|utmctr=View%20this|utmcct=52%%20off", msa=0x7fff7bc66870) at regexec.c:2433 #1 0x00002b785390329c in onig_search (reg=0xcce4a00, str=0xd47b101 "206193045.1297252703.66.40.utmcsr=sendmail|utmccn=52%%20off|utmcmd=email|utmctr=View%20this|utmcct=52%%20off", end=0xd47b1a6 "", start=&lt;value optimized out&gt;, range=0xd47b102 "06193045.1297252703.66.40.utmcsr=sendmail|utmccn=52%%20off|utmcmd=email|utmctr=View%20this|utmcct=52%%20off", region=0x7fff7bc66990, option=0) at regexec.c:3646 #2 0x00002b78538ef51e in rb_reg_search (re=137570880, str=218457520, pos=0, reverse=0) at re.c:1372 #3 0x00002b78538efc42 in rb_reg_match (re=214846549, str=218457520) at re.c:2740 #4 0x00002b7853971c36 in vm_exec_core (th=0x8329020, initial=&lt;value optimized out&gt;) at insns.def:2089 #5 0x00002b7853979b99 in vm_exec (th=0xcce4c55) at vm.c:1147 #6 0x00002b7853970cd9 in invoke_block_from_c (th=0x8329020, block=0x2b78572fea38, self=174397400, argc=1, argv=0x0, blockptr=0x0, cref=0x0) at vm.c:558 #7 0x00002b785397b037 in vm_yield (val=218457520) at vm.c:588 #8 rb_yield_0 (val=218457520) at vm_eval.c:740 #9 rb_yield (val=218457520) at vm_eval.c:750 #10 0x00002b7853840926 in rb_ary_collect (ary=218457680) at array.c:2166 #11 0x00002b78539716aa in vm_call_cfunc (th=0x8329020, cfp=0x2b78572fea10, num=0, blockptr=0x2b78572fea39, flag=0, id=1544, me=0x83e0ac0, recv=218457680) at vm_insnhelper.c:402 #12 vm_call_method (th=0x8329020, cfp=0x2b78572fea10, num=0, blockptr=0x2b78572fea39, flag=0, id=1544, me=0x83e0ac0, recv=218457680) at vm_insnhelper.c:524 #13 0x00002b785397438c in vm_exec_core (th=0x8329020, initial=&lt;value optimized out&gt;) at insns.def:1006 #14 0x00002b7853979b99 in vm_exec (th=0xcce4c55) at vm.c:1147 #15 0x00002b7853970cd9 in invoke_block_from_c (th=0x8329020, block=0x2b78572feb40, self=174397400, argc=1, argv=0x0, blockptr=0x0, cref=0x0) at vm.c:558 #16 0x00002b785397b037 in vm_yield (val=218460560) at vm.c:588 #17 rb_yield_0 (val=218460560) at vm_eval.c:740 #18 rb_yield (val=218460560) at vm_eval.c:750 #19 0x00002b785383bc9c in rb_ary_each (ary=218460960) at array.c:1427 #20 0x00002b78539716aa in vm_call_cfunc (th=0x8329020, cfp=0x2b78572feb18, num=0, blockptr=0x2b78572feb41, flag=0, id=424, me=0x83dfb90, recv=218460960) at vm_insnhelper.c:402 #21 vm_call_method (th=0x8329020, cfp=0x2b78572feb18, num=0, blockptr=0x2b78572feb41, flag=0, id=424, me=0x83dfb90, recv=218460960) at vm_insnhelper.c:524 #22 0x00002b785397438c in vm_exec_core (th=0x8329020, initial=&lt;value optimized out&gt;) at insns.def:1006 #23 0x00002b7853979b99 in vm_exec (th=0xcce4c55) at vm.c:1147 #24 0x00002b785396b4e5 in vm_call0 (th=0x8329020, recv=180469600, id=384, argc=2, argv=0x7fff7bc67990, me=0xd47b130) at vm_eval.c:66 #25 0x00002b785396d354 in vm_method_missing (th=0x8329020, id=1513486, recv=180469600, num=&lt;value optimized out&gt;, blockptr=0x0, opt=0) ---Type &lt;return&gt; to continue, or q &lt;return&gt; to quit--- at vm_insnhelper.c:448 #26 0x00002b78539715e3 in vm_call_method (th=0x8329020, cfp=0x0, num=1, blockptr=0x0, flag=0, id=5912, me=0x0, recv=180469600) at vm_insnhelper.c:666 #27 0x00002b785397438c in vm_exec_core (th=0x8329020, initial=&lt;value optimized out&gt;) at insns.def:1006 #28 0x00002b7853979b99 in vm_exec (th=0xcce4c55) at vm.c:1147 #29 0x00002b7853970cd9 in invoke_block_from_c (th=0x8329020, block=0x2b78572ffa60, self=218506160, argc=1, argv=0x0, blockptr=0x0, cref=0x0) at vm.c:558 #30 0x00002b785397ad01 in rb_yield_0 (tag=30793742, data=&lt;value optimized out&gt;) at vm.c:588 #31 catch_i (tag=30793742, data=&lt;value optimized out&gt;) at vm_eval.c:1459 #32 0x00002b7853968483 in rb_catch_obj (tag=30793742, func=0x2b785397acc0 &lt;catch_i&gt;, data=0) at vm_eval.c:1534 #33 0x00002b785396978d in rb_f_catch (argc=&lt;value optimized out&gt;, argv=&lt;value optimized out&gt;) at vm_eval.c:1510 #34 0x00002b78539716aa in vm_call_cfunc (th=0x8329020, cfp=0x2b78572ffa38, num=1, blockptr=0x2b78572ffa61, flag=8, id=2840, me=0x83b2250, recv=218506160) at vm_insnhelper.c:402 #35 vm_call_method (th=0x8329020, cfp=0x2b78572ffa38, num=1, blockptr=0x2b78572ffa61, flag=8, id=2840, me=0x83b2250, recv=218506160) at vm_insnhelper.c:524 #36 0x00002b785397438c in vm_exec_core (th=0x8329020, initial=&lt;value optimized out&gt;) at insns.def:1006 #37 0x00002b7853979b99 in vm_exec (th=0xcce4c55) at vm.c:1147 #38 0x00002b785396b4e5 in vm_call0 (th=0x8329020, recv=218506160, id=40296, argc=1, argv=0x7fff7bc685e0, me=0xd47b130) at vm_eval.c:66 #39 0x00002b785396bf9a in rb_call0 (recv=218506160, mid=40296, n=1) at vm_eval.c:235 #40 rb_call (recv=218506160, mid=40296, n=1) at vm_eval.c:438 #41 rb_funcall (recv=218506160, mid=40296, n=1) at vm_eval.c:638 #42 0x00002aaaac565bb6 in event_callback_wrapper (a1=&lt;value optimized out&gt;, a2=&lt;value optimized out&gt;, a3=&lt;value optimized out&gt;, a4=&lt;value optimized out&gt;) at rubymain.cpp:162 #43 0x00002aaaac555688 in ConnectionDescriptor::_DispatchInboundData (this=0xca4a060, buffer=0x7fff7bc654e0 "\001", size=1402620608) at ed.cpp:770 #44 0x00002aaaac55571f in ConnectionDescriptor::Read (this=0xca4a060) at ed.cpp:718 #45 0x00002aaaac55e969 in EventMachine_t::_RunEpollOnce (this=0xc874530) at em.cpp:488 #46 0x00002aaaac55ec46 in EventMachine_t::_RunOnce (this=0xcce4c55) at em.cpp:451 #47 0x00002aaaac55ec93 in EventMachine_t::Run (this=0xc874530) at em.cpp:432 #48 0x00002aaaac565629 in t_run_machine_without_threads (self=214846549) at rubymain.cpp:185 #49 0x00002b78539716aa in vm_call_cfunc (th=0x8329020, cfp=0x2b78572ffbf0, num=0, blockptr=0x1, flag=24, id=39400, me=0x9055d80, recv=139822160) at vm_insnhelper.c:402 #50 vm_call_method (th=0x8329020, cfp=0x2b78572ffbf0, num=0, blockptr=0x1, flag=24, id=39400, me=0x9055d80, recv=139822160) at vm_insnhelper.c:524 #51 0x00002b785397438c in vm_exec_core (th=0x8329020, initial=&lt;value optimized out&gt;) at insns.def:1006 #52 0x00002b7853979b99 in vm_exec (th=0xcce4c55) at vm.c:1147 #53 0x00002b7853979ff7 in rb_iseq_eval (iseqval=145595680) at vm.c:1374 #54 0x00002b785386d741 in rb_load_internal (fname=145597920, wrap=&lt;value optimized out&gt;) at load.c:294 #55 0x00002b785386d8a1 in rb_f_load (argc=&lt;value optimized out&gt;, argv=&lt;value optimized out&gt;) at load.c:367 #56 0x00002b78539716aa in vm_call_cfunc (th=0x8329020, cfp=0x2b78572fff08, num=1, blockptr=0x1, flag=8, id=5944, me=0x8421cd0, recv=137928280) at vm_insnhelper.c:402 #57 vm_call_method (th=0x8329020, cfp=0x2b78572fff08, num=1, blockptr=0x1, flag=8, id=5944, me=0x8421cd0, recv=137928280) ---Type &lt;return&gt; to continue, or q &lt;return&gt; to quit--- at vm_insnhelper.c:524 #58 0x00002b785397438c in vm_exec_core (th=0x8329020, initial=&lt;value optimized out&gt;) at insns.def:1006 #59 0x00002b7853979b99 in vm_exec (th=0xcce4c55) at vm.c:1147 #60 0x00002b7853979e74 in rb_iseq_eval_main (iseqval=145661040) at vm.c:1388 #61 0x00002b785386ae52 in ruby_exec_internal (n=0x8ae9c70) at eval.c:214 #62 0x00002b785386ae79 in ruby_exec_node (n=0x8ae9c70) at eval.c:261 #63 0x00002b785386d1bf in ruby_run_node (n=0x8ae9c70) at eval.c:254 #64 0x00000000004008ef in main (argc=10, argv=0x7fff7bc6df78) at main.c:35 </code></pre> <p>What I can deduce from this:</p> <ul> <li>It's hanging on a regular expression performed on something like <code>52%%20off|utmcmd=email|utmctr=View%20this|utmcct=52%%20off</code>, which appears to be a bastardized form of a query string (any insights on why it's pipes rather than ampersands?). I don't know what the regex they're looking for is, though (any way I can find it?).</li> <li>It's getting through thin/eventmachine just fine to the rails stack just fine because at <code>#42</code>, it seems to be initializing an <code>event_callback_wrapper</code>, which I take to mean that it's handing it off to the next step in Rack.</li> </ul> <p>And a weird thing:</p> <ul> <li><code>netstat</code> doesn't list any outstanding connections, and <code>nginx</code> logs don't show any requests, successful, unsuccessful, or abandoned, with the query string implied by the string that shows up in the backtrace.</li> </ul> <p>Other things I've tried:</p> <p>I've tried just going into gdb and nexting a bunch of times, and it just goes in a loopish manner. I've also tried using <a href="http://www.rubyinside.com/hijack-get-a-live-irb-prompt-for-any-existing-ruby-process-2232.html" rel="nofollow">hijack</a>, but I couldn't find anything useful to do.</p> <p>Things that might be useful that I don't know how to do or whether they are possible:</p> <ul> <li>Get an actual ruby code stack.</li> <li>Figure out what's calling the regex.</li> <li>Nailing down what the regex actually is and what it's being matched against.</li> </ul> <p>Any other advice or whatnot would be greatly appreciated.</p>
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    1. USSteven Xu
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    1. COI think this one should go to ServerFault.
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    2. CONot sure if it is of any help, but the string is probably not an URL, but the content of a Google Analytics tracking cookie: http://helpful.knobs-dials.com/index.php/Utma,_utmb,_utmz_cookies
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      1. USMladen Jablanović
    3. CO@Mladen: great observation! I'll see what I can do with that.
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