This signal handler was calling non-trivial functions that performed
signal-unsafe work. In particular, attempts to interact with the system
allocator. Quoting downstream discussion:¹

  On Mon, 4 Mar 2013 21:26:40 -0600, Jeff Epler wrote:
  > On Sun, Mar 03, 2013 at 12:20:57PM +0000, Steven Chamberlain wrote:
  > > > #5  0x0000000800d21f2c in *__GI___libc_free (mem=<optimized out>) at malloc.c:3736
  > > >         ar_ptr = 0x800ff3240
  > > >         p = <optimized out>
  > > > #6  0x0000000800844a79 in gvFreeContext () from /usr/lib/libgvc.so.5
  > > > No symbol table info available.
  > > > #7  0x0000000000400fd8 in ?? ()
  > > > No symbol table info available.
  > > > #8  0x000000080389bf04 in __pthread_sighandler
  >
  > As many of you are probably aware, it's not permitted in POSIX to call free()
  > in signal handler context without some additional guarantees about what the
  > interrupted function may be.
  > http://pubs.opengroup.org/onlinepubs/9699919799/func...