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  1. Traffic Server
  2. TS-5076

NetVC is lost from read or write enable_list

Details

    • Bug
    • Status: Resolved
    • Major
    • Resolution: Fixed
    • None
    • 6.2.1, 7.1.0
    • Network
    • None

    Description

      The related code here:

      void
      UnixNetVConnection::reenable(VIO *vio)
      {
        if (STATE_FROM_VIO(vio)->enabled)
          return;
        set_enabled(vio);
        if (!thread)
          return;
        EThread *t = vio->mutex->thread_holding;
        ink_assert(t == this_ethread());
        ink_release_assert(!closed);
        if (nh->mutex->thread_holding == t) { 
      ...
          MUTEX_TRY_LOCK(lock, nh->mutex, t);
          if (!lock.is_locked()) {
            if (vio == &read.vio) {
              if (!read.in_enabled_list) {    // -----------> the condition check is not atomic
                read.in_enabled_list = 1;   // -----------> the variable set is not atomic
                nh->read_enable_list.push(this);
              }
            } else {
              if (!write.in_enabled_list) {   // -----------> the write side 
                write.in_enabled_list = 1;  // -----------> the write side
                nh->write_enable_list.push(this);
              }
            }
            if (nh->trigger_event && nh->trigger_event->ethread->signal_hook)
              nh->trigger_event->ethread->signal_hook(nh->trigger_event->ethread);
          } else {
      ...
          }
        }
      }
      

      Due to the unstable condition check code, the nh->read_enable_list.push(this) would push a netvc into atomic queue that is already inside a queue.

      It leads the elements in atomic queue after the netvc will be lost.

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            oknet Chao Xu
            oknet Chao Xu
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              Resolved:

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