[tbb-bugs] #21766 [Applications/Tor Browser]: Tor Browser based on ESR52 with e10s enabled crashed whle trying to download a file

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#21766: Tor Browser based on ESR52 with e10s enabled crashed whle trying to
download a file
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 Reporter:  gk                                   |          Owner:  tbb-
                                                 |  team
     Type:  defect                               |         Status:  new
 Priority:  Very High                            |      Milestone:
Component:  Applications/Tor Browser             |        Version:
 Severity:  Critical                             |     Resolution:
 Keywords:  tbb-7.0-must, ff52-esr,              |  Actual Points:
  TorBrowserTeam201703, tbb-7.0-must-nightly     |
Parent ID:                                       |         Points:
 Reviewer:                                       |        Sponsor:
                                                 |  Sponsor4
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Comment (by mcs):

 Kathy and I tried to debug this problem. The main thing we learned is that
 we are not yet good at understanding e10s-related problems :)

 What we do know is that the main (chrome) process is killing the content
 process (which is associated with the tab where the download is
 initiated). Code inside the KillProcess() function within
 ipc/chromium/src/base/process_util_posix.cc sends a SIGTERM to the content
 process . But why? The key hint seems to be this log message:

  ###!!! [Parent][DispatchAsyncMessage] Error:
 PExternalHelperApp::Msg_DivertToParentUsing Route error: message sent to
 unknown actor ID

 I will attach a call stack that shows how the code gets there, but Kathy
 and I don't know the answer to the really important question: "Why?". Our
 best guess is that we should not be trying to use the prompt service from
 the chrome process at all, but that seems surprising.

 Does anyone know how we can learn more about what APIs can safely be used
 from which kind of process? Or maybe we should just ask some Mozilla
 engineers?

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/21766#comment:5>
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