[tor-bugs] #31614 [Core Tor/Tor]: Implement clean_up_backtrace_handler()

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#31614: Implement clean_up_backtrace_handler()
-------------------------------------------------+-------------------------
 Reporter:  teor                                 |          Owner:  teor
     Type:  defect                               |         Status:
                                                 |  needs_revision
 Priority:  Medium                               |      Milestone:  Tor:
                                                 |  0.4.2.x-final
Component:  Core Tor/Tor                         |        Version:  Tor:
                                                 |  0.3.5.1-alpha
 Severity:  Normal                               |     Resolution:
 Keywords:  consider-backport-after-042-stable,  |  Actual Points:  0.2
  consider-backport-if-needed, diagnostics,      |
  042-should, 035-backport-maybe, 040-backport-  |
  maybe, 041-backport-maybe, regression,         |
  BugSmashFund                                   |
Parent ID:                                       |         Points:  0.2
 Reviewer:  dgoulet                              |        Sponsor:
-------------------------------------------------+-------------------------

Comment (by teor):

 You're right, there are a bunch of nasty race conditions here.

 This is what we need to fix:
 1. Always lock the mutex before using cb_buf (there are some places where
 we don't do this)
 2. Lock the mutex before adding or removing signal handlers (might not be
 strictly required, but it makes reasoning about locks easier)
 3. Abort if destroying the mutex fails (doesn't save us from undefined
 behaviour, but does notify us when it happens)

 We could also
 4. Lock a mutex before logging anywhere in the err module (this could
 cause more issues than it solves)

 The best way to do this might be to put cb_buf in its own file, and use
 accessor functions.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/31614#comment:11>
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