[Bug 1748597] Re: Please backport fix for bugs.debian.org/827015

[David Bartley]

Thanks, I've updated the description to outline the impact, and attached
the two patches from the upstream Debian package that should be applied.

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https://bugs.launchpad.net/bugs/1748597

Title:
  Please backport fix for bugs.debian.org/827015

Status in libunwind package in Ubuntu:
  New
Status in libunwind package in Debian:
  Unknown

Bug description:
  [Impact]
  When a C++ exception is thrown with libunwind linked in, the signal mask is corrupted.

  For MongoDB, if the CPU profiler is enabled (which requires linking
  libunwind), any exception that is raised within the server may cause
  random signals to become unblocked on a thread.  If SIGTERM becomes
  unblocked on any thread but the main thread, the server won't exit
  cleanly (this is particularly evident when running the MongoDB test
  suite, which starts/stops servers repeatedly).

  This also seems to impact Pyston:
  https://lab.nexedi.com/Daetalus/Pyston/commit/1bac7510861a112a9023f821bf3e857a6fb45037

  [Test Case]
  I've attached the test case from the upstream Debian bug (https://bugs.debian.org/827015).

  $ g++ sigtest.cpp -lpthread
  Signals blocked: 1 (Hangup)	65 (Unknown signal 65)
  Throw exception
  Signals blocked: 1 (Hangup)	65 (Unknown signal 65)

  $ g++ sigtest.cpp -lpthread -lunwind
  Signals blocked: 1 (Hangup)	65 (Unknown signal 65)
  Throw exception
  Signals blocked: 7 (Bus error)	8 (Floating point exception)	10 (User defined signal 1)	12 (User defined signal 2)	13 (Broken pipe)	15 (Terminated)	17 (Child exited)	20 (Stopped)21 (Stopped (tty input))	25 (File size limit exceeded)	26 (Virtual timer expired)	27 (Profiling timer expired)	28 (Window changed)	29 (I/O possible)	30 (Power failure)	31 (Bad system call)	32 (Unknown signal 32)	33 (Unknown signal 33)	34 (Real-time signal 0)	35 (Real-time signal 1)	36 (Real-time signal 2)	37 (Real-time signal 3)	38 (Real-time signal 4)	39 (Real-time signal 5)	40 (Real-time signal 6)	41 (Real-time signal 7)	42 (Real-time signal 8)	43 (Real-time signal 9)	44 (Real-time signal 10)	45 (Real-time signal 11)	46 (Real-time signal 12)	47 (Real-time signal 13)	65 (Unknown signal 65)

  [Regression Potential]
  This fix is already present in bionic and Debian testing, and has been for a couple months.  The upstream fix has existed for over a year.

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