[tor-bugs] #29497 [Applications/Tor Browser]: After tor crash, firefox.exe (tor browser) shoots up to 50+% cpu usage and stays there til killed in task list

Tor Bug Tracker & Wiki blackhole at torproject.org
Tue Feb 19 15:37:26 UTC 2019


#29497: After tor crash, firefox.exe (tor browser) shoots up to 50+% cpu usage and
stays there til killed in task list
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 Reporter:  cypherpunks               |          Owner:  tbb-team
     Type:  defect                    |         Status:  new
 Priority:  High                      |      Milestone:
Component:  Applications/Tor Browser  |        Version:  Tor: unspecified
 Severity:  Normal                    |     Resolution:
 Keywords:                            |  Actual Points:
Parent ID:                            |         Points:
 Reviewer:                            |        Sponsor:
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Comment (by mcs):

 Kathy and I spent a little time on this ticket to try to narrow down when
 this problem was introduced. We were able to reproduce the problem on
 macOS with Tor Browser 8.0 or newer (and it is probably reproducible using
 any esr60-based Tor Browser).

 Here are the steps we followed:
 1. Open a clean Tor Browser.
 2. Click Connect to connect directly to the Tor network.
 3. Send a TERM signal to the tor.real process (e.g., `killall tor.real`)
 4. Dismiss the "Tor unexpectedly exited" prompt.

 At that point, the main Firefox process will be in a busy loop (consuming
 approximately 100% CPU). We could not reproduce the problem with Tor
 Browser 7.5.6 (the last esr52-based release).

 As other people have pointed out, the only way to recover from this
 condition seems to be to restart the browser. We have not tracked down the
 exact cause, but when it is in this state the firefox process seems to be
 making a lot of `select()` system calls.

 We also did an experiment where we disabled Tor Launcher, started a
 standalone copy of tor.real in TCP port 9150, and then started Tor Browser
 (we wanted to make sure the code in Tor Launcher that monitors the control
 port was not at fault). The 100% CPU issue also occurred after we killed
 that copy of `tor.real`. This combined with the high frequency of
 `select()` calls suggests that there may be a bug in Tor Browser's SOCKS
 code. A good next step would be to try to reproduce this issue with
 Firefox.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/29497#comment:2>
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