Consing inside without-gcing on sb-safepoint

[Robert Brown]

Recently built SBCL binaries on Linux x64 are hanging when running the
backtrace test in threads.impure.lisp.

Attached are the C and Lisp backtraces ....

[Stas Boukarev (stassats)]

Test case:
(format t "~a~%" (sb-unix:unix-getpid))

(defun test ()
  (let ((threads
          (loop repeat 15
                collect (sb-thread:make-thread
                         (lambda ()
                           (let ((threads (sb-thread:list-all-threads)))
                             (dotimes (i 100000)
                               (with-output-to-string (stream)
                                 (let ((*print-pretty* nil)
                                       (*print-circle* t))
                                   (princ threads stream))))))))))
    (mapc #'sb-thread:join-thread threads)))

[Stas Boukarev (stassats)]

New test-case:
(format t "~a~%" (sb-unix:unix-getpid))

(defun do-something (x)
  (sb-sys:without-gcing
    (copy-seq x)))

(defun test ()
  (mapc #'sb-thread:join-thread
        (loop repeat 8
              collect
              (sb-thread:make-thread
               (lambda ()
                 (dotimes (i 100000000)
                   (let ((vector (make-array 1000)))
                     (loop for i to 1000
                           do
                           (do-something vector)))))))))

(test)

[Alastair Bridgewater (alastair-bridgewater)]

Commits 229d6eb7478904ad5228ea6a6bd3fa67053e2198, 5338e756b46022ef748b969cfc56f9053fe46b2e, and bcc6a2d83b6cd64322ab63600e2af6db103c5d49 all address various deadlock scenarios exercised by the test case in comment #3.