macOS: extend the workaround to cover the dyld/exc_server deadlock is…

…sue, since 12.1

Later, we should probably switch to using mach_exc_server generated from
`mig mach_exc.defs`.

src/signals-mach.c

@@ -526,27 +526,30 @@ static kern_return_t profiler_segv_handler
 }
 #endif
 
-static int jl_lock_profile_mach(void)
+// WARNING: we are unable to handle sigsegv while the dlsymlock is held
+static int jl_lock_profile_mach(int dlsymlock)
 {
  jl_lock_profile();
+ // workaround for old keymgr bugs
  void *unused = NULL;
  int keymgr_locked = _keymgr_get_and_lock_processwide_ptr_2(KEYMGR_GCC3_DW2_OBJ_LIST, &unused) == 0;
- if (_dyld_atfork_prepare != NULL && _dyld_atfork_parent != NULL)
+ // workaround for new dlsym4 bugs (API and bugs introduced in macOS 12.1)
+ if (dlsymlock && _dyld_atfork_prepare != NULL && _dyld_atfork_parent != NULL)
  _dyld_atfork_prepare();
  return keymgr_locked;
 }
 
-static void jl_unlock_profile_mach(int keymgr_locked)
+static void jl_unlock_profile_mach(int dlsymlock, int keymgr_locked)
 {
- if (_dyld_atfork_prepare != NULL && _dyld_atfork_parent != NULL)
- _dyld_atfork_parent();
+ if (dlsymlock && _dyld_atfork_prepare != NULL && _dyld_atfork_parent != NULL) \
+ _dyld_atfork_parent(); \
  if (keymgr_locked)
  _keymgr_unlock_processwide_ptr(KEYMGR_GCC3_DW2_OBJ_LIST);
  jl_unlock_profile();
 }
 
-#define jl_lock_profile() int keymgr_locked = jl_lock_profile_mach()
-#define jl_unlock_profile() jl_unlock_profile_mach(keymgr_locked)
+#define jl_lock_profile() int keymgr_locked = jl_lock_profile_mach(1)
+#define jl_unlock_profile() jl_unlock_profile_mach(1, keymgr_locked)
 
 void *mach_profile_listener(void *arg)
 {
@@ -564,7 +567,7 @@ void *mach_profile_listener(void *arg)
  HANDLE_MACH_ERROR("mach_msg", ret);
  // sample each thread, round-robin style in reverse order
  // (so that thread zero gets notified last)
- jl_lock_profile();
+ int keymgr_locked = jl_lock_profile_mach(0);
  jl_shuffle_int_array_inplace(profile_round_robin_thread_order, jl_n_threads, &profile_cong_rng_seed);
  for (int idx = jl_n_threads; idx-- > 0; ) {
  // Stop the threads in the random round-robin order.
@@ -575,9 +578,13 @@ void *mach_profile_listener(void *arg)
  break;
  }
 
+ if (_dyld_atfork_prepare != NULL && _dyld_atfork_parent != NULL)
+ _dyld_atfork_prepare(); // briefly acquire the dlsym lock
  host_thread_state_t state;
  jl_thread_suspend_and_get_state2(i, &state);
  unw_context_t *uc = (unw_context_t*)&state;
+ if (_dyld_atfork_prepare != NULL && _dyld_atfork_parent != NULL)
+ _dyld_atfork_parent(); // quickly release the dlsym lock
 
  if (running) {
 #ifdef LLVMLIBUNWIND
@@ -634,7 +641,7 @@ void *mach_profile_listener(void *arg)
  // We're done! Resume the thread.
  jl_thread_resume(i, 0);
  }
- jl_unlock_profile();
+ jl_unlock_profile_mach(0, keymgr_locked);
  if (running) {
  // Reset the alarm
  kern_return_t ret = clock_alarm(clk, TIME_RELATIVE, timerprof, profile_port);