[tor-bugs] #30187 [Core Tor/Tor]: 100% cpu usage in winthreads tor_cond_wait

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#30187: 100% cpu usage in winthreads tor_cond_wait
--------------------------------------+------------------------------
 Reporter:  bolvan                    |          Owner:  (none)
     Type:  defect                    |         Status:  new
 Priority:  Medium                    |      Component:  Core Tor/Tor
  Version:  Tor: 0.3.5.8              |       Severity:  Normal
 Keywords:  winthreads tor_cond_wait  |  Actual Points:
Parent ID:                            |         Points:
 Reviewer:                            |        Sponsor:
--------------------------------------+------------------------------
 For years I run relay using self-compiled win64 version of tor.
 Compiler mingw64.
 Relay runs well for some time but suddenly starts using 100% cpu all
 cores.
 I traced where it happens. The following loop never ends :

 {{{

   do {
     DWORD res;
     res = WaitForSingleObject(cond->event, ms);
     EnterCriticalSection(&cond->lock);
     if (cond->n_to_wake &&
         cond->generation != generation_at_start) {
       --cond->n_to_wake;
       --cond->n_waiting;
       result = 0;
       waiting = 0;
       goto out;
     } else if (res != WAIT_OBJECT_0) {
       result = (res==WAIT_TIMEOUT) ? 1 : -1;
       --cond->n_waiting;
       waiting = 0;
       goto out;
     } else if (ms != INFINITE) {
       endTime = GetTickCount();
       if (startTime + ms_orig <= endTime) {
         result = 1; /* Timeout */
         --cond->n_waiting;
         waiting = 0;
         goto out;
       } else {
         ms = startTime + ms_orig - endTime;
       }
     }
     /* If we make it here, we are still waiting. */
     if (cond->n_to_wake == 0) {
       /* There is nobody else who should wake up; reset
        * the event. */
       ResetEvent(cond->event);
     }
   out:
     LeaveCriticalSection(&cond->lock);
   } while (waiting);

 }}}


 res = WAIT_OBJECT_0;
 ms = INFINITE;
 cond->n_to_wake=0x11
 cond->generation=0x28
 generation_at_start=0x28


 it means no path with "goto out" ever execute
 more than one thread run this loop and each one eat separate core

 Some people I shared binaries with report same problem.
 Pls check

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/30187>
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