handle some cases of null Task in segv handling (JuliaLang#42836)

Also ensure we do not use round-robin sampling when printing a critical
error, only for profiling.

src/gf.c

@@ -1829,7 +1829,7 @@ static void JL_NORETURN jl_method_error_bare(jl_function_t *f, jl_value_t *args,
  jl_static_show((JL_STREAM*)STDERR_FILENO,args); jl_printf((JL_STREAM*)STDERR_FILENO,"\n");
  jl_ptls_t ptls = jl_current_task->ptls;
  ptls->bt_size = rec_backtrace(ptls->bt_data, JL_MAX_BT_SIZE, 0);
- jl_critical_error(0, NULL);
+ jl_critical_error(0, NULL, jl_current_task);
  abort();
  }
  // not reached

src/julia_internal.h

@@ -1013,7 +1013,7 @@ size_t rec_backtrace_ctx(jl_bt_element_t *bt_data, size_t maxsize, bt_context_t
 size_t rec_backtrace_ctx_dwarf(jl_bt_element_t *bt_data, size_t maxsize, bt_context_t *ctx, jl_gcframe_t *pgcstack) JL_NOTSAFEPOINT;
 #endif
 JL_DLLEXPORT jl_value_t *jl_get_backtrace(void);
-void jl_critical_error(int sig, bt_context_t *context);
+void jl_critical_error(int sig, bt_context_t *context, jl_task_t *ct);
 JL_DLLEXPORT void jl_raise_debugger(void);
 int jl_getFunctionInfo(jl_frame_t **frames, uintptr_t pointer, int skipC, int noInline) JL_NOTSAFEPOINT;
 JL_DLLEXPORT void jl_gdblookup(void* ip) JL_NOTSAFEPOINT;

src/signal-handling.c

@@ -241,19 +241,20 @@ void jl_show_sigill(void *_ctx)
 }
 
 // what to do on a critical error on a thread
-void jl_critical_error(int sig, bt_context_t *context)
+void jl_critical_error(int sig, bt_context_t *context, jl_task_t *ct)
 {
 
- jl_task_t *ct = jl_current_task;
- jl_bt_element_t *bt_data = ct->ptls->bt_data;
- size_t *bt_size = &ct->ptls->bt_size;
- size_t i, n = *bt_size;
+ jl_bt_element_t *bt_data = ct ? ct->ptls->bt_data : NULL;
+ size_t *bt_size = ct ? &ct->ptls->bt_size : NULL;
+ size_t i, n = ct ? *bt_size : 0;
  if (sig) {
  // kill this task, so that we cannot get back to it accidentally (via an untimely ^C or jlbacktrace in jl_exit)
  jl_set_safe_restore(NULL);
- ct->gcstack = NULL;
- ct->eh = NULL;
- ct->excstack = NULL;
+ if (ct) {
+ ct->gcstack = NULL;
+ ct->eh = NULL;
+ ct->excstack = NULL;
+ }
 #ifndef _OS_WINDOWS_
  sigset_t sset;
  sigemptyset(&sset);
@@ -277,7 +278,7 @@ void jl_critical_error(int sig, bt_context_t *context)
  jl_safe_printf("\nsignal (%d): %s\n", sig, strsignal(sig));
  }
  jl_safe_printf("in expression starting at %s:%d\n", jl_filename, jl_lineno);
- if (context) {
+ if (context && ct) {
  // Must avoid extended backtrace frames here unless we're sure bt_data
  // is properly rooted.
  *bt_size = n = rec_backtrace_ctx(bt_data, JL_MAX_BT_SIZE, context, NULL);

src/signals-mach.c

@@ -402,7 +402,7 @@ static void jl_try_deliver_sigint(void)
 static void JL_NORETURN jl_exit_thread0_cb(int exitstate)
 {
 CFI_NORETURN
- jl_critical_error(exitstate - 128, NULL);
+ jl_critical_error(exitstate - 128, NULL, jl_current_task);
  jl_exit(exitstate);
 }
 

src/signals-unix.c

@@ -231,7 +231,7 @@ static void sigdie_handler(int sig, siginfo_t *info, void *context)
  uv_tty_reset_mode();
  if (sig == SIGILL)
  jl_show_sigill(context);
- jl_critical_error(sig, jl_to_bt_context(context));
+ jl_critical_error(sig, jl_to_bt_context(context), jl_get_current_task());
  if (sig != SIGSEGV &&
  sig != SIGBUS &&
  sig != SIGILL) {
@@ -410,7 +410,7 @@ CFI_NORETURN
  // (unavoidable due to its async nature).
  // Try harder to exit each time if we get multiple exit requests.
  if (thread0_exit_count <= 1) {
- jl_critical_error(thread0_exit_state - 128, NULL);
+ jl_critical_error(thread0_exit_state - 128, NULL, jl_current_task);
  jl_exit(thread0_exit_state);
  }
  else if (thread0_exit_count == 2) {
@@ -747,71 +747,72 @@ static void *signal_listener(void *arg)
  unw_context_t *signal_context;
  // sample each thread, round-robin style in reverse order
  // (so that thread zero gets notified last)
- if (critical || profile)
+ if (critical || profile) {
  jl_lock_profile();
- 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.
- int i = profile_round_robin_thread_order[idx];
- // notify thread to stop
- jl_thread_suspend_and_get_state(i, &signal_context);
-
- // do backtrace on thread contexts for critical signals
- // this part must be signal-handler safe
- if (critical) {
- bt_size += rec_backtrace_ctx(bt_data + bt_size,
- JL_MAX_BT_SIZE / jl_n_threads - 1,
- signal_context, NULL);
- bt_data[bt_size++].uintptr = 0;
- }
-
- // do backtrace for profiler
- if (profile && running) {
- if (jl_profile_is_buffer_full()) {
- // Buffer full: Delete the timer
- jl_profile_stop_timer();
+ if (!critical)
+ 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.
+ int i = critical ? idx : profile_round_robin_thread_order[idx];
+ // notify thread to stop
+ jl_thread_suspend_and_get_state(i, &signal_context);
+
+ // do backtrace on thread contexts for critical signals
+ // this part must be signal-handler safe
+ if (critical) {
+ bt_size += rec_backtrace_ctx(bt_data + bt_size,
+ JL_MAX_BT_SIZE / jl_n_threads - 1,
+ signal_context, NULL);
+ bt_data[bt_size++].uintptr = 0;
  }
- else {
- // unwinding can fail, so keep track of the current state
- // and restore from the SEGV handler if anything happens.
- jl_jmp_buf *old_buf = jl_get_safe_restore();
- jl_jmp_buf buf;
-
- jl_set_safe_restore(&buf);
- if (jl_setjmp(buf, 0)) {
- jl_safe_printf("WARNING: profiler attempt to access an invalid memory location\n");
- } else {
- // Get backtrace data
- bt_size_cur += rec_backtrace_ctx((jl_bt_element_t*)bt_data_prof + bt_size_cur,
- bt_size_max - bt_size_cur - 1, signal_context, NULL);
- }
- jl_set_safe_restore(old_buf);
-
- jl_ptls_t ptls = jl_all_tls_states[i];
-
- // store threadid but add 1 as 0 is preserved to indicate end of block
- bt_data_prof[bt_size_cur++].uintptr = ptls->tid + 1;
-
- // store task id
- bt_data_prof[bt_size_cur++].jlvalue = (jl_value_t*)jl_atomic_load_relaxed(&ptls->current_task);
-
- // store cpu cycle clock
- bt_data_prof[bt_size_cur++].uintptr = cycleclock();
 
- // store whether thread is sleeping but add 1 as 0 is preserved to indicate end of block
- bt_data_prof[bt_size_cur++].uintptr = jl_atomic_load_relaxed(&ptls->sleep_check_state) + 1;
-
- // Mark the end of this block with two 0's
- bt_data_prof[bt_size_cur++].uintptr = 0;
- bt_data_prof[bt_size_cur++].uintptr = 0;
+ // do backtrace for profiler
+ if (profile && running) {
+ if (jl_profile_is_buffer_full()) {
+ // Buffer full: Delete the timer
+ jl_profile_stop_timer();
+ }
+ else {
+ // unwinding can fail, so keep track of the current state
+ // and restore from the SEGV handler if anything happens.
+ jl_jmp_buf *old_buf = jl_get_safe_restore();
+ jl_jmp_buf buf;
+
+ jl_set_safe_restore(&buf);
+ if (jl_setjmp(buf, 0)) {
+ jl_safe_printf("WARNING: profiler attempt to access an invalid memory location\n");
+ } else {
+ // Get backtrace data
+ bt_size_cur += rec_backtrace_ctx((jl_bt_element_t*)bt_data_prof + bt_size_cur,
+ bt_size_max - bt_size_cur - 1, signal_context, NULL);
+ }
+ jl_set_safe_restore(old_buf);
+
+ jl_ptls_t ptls = jl_all_tls_states[i];
+
+ // store threadid but add 1 as 0 is preserved to indicate end of block
+ bt_data_prof[bt_size_cur++].uintptr = ptls->tid + 1;
+
+ // store task id
+ bt_data_prof[bt_size_cur++].jlvalue = (jl_value_t*)jl_atomic_load_relaxed(&ptls->current_task);
+
+ // store cpu cycle clock
+ bt_data_prof[bt_size_cur++].uintptr = cycleclock();
+
+ // store whether thread is sleeping but add 1 as 0 is preserved to indicate end of block
+ bt_data_prof[bt_size_cur++].uintptr = jl_atomic_load_relaxed(&ptls->sleep_check_state) + 1;
+
+ // Mark the end of this block with two 0's
+ bt_data_prof[bt_size_cur++].uintptr = 0;
+ bt_data_prof[bt_size_cur++].uintptr = 0;
+ }
  }
- }
 
- // notify thread to resume
- jl_thread_resume(i, sig);
- }
- if (critical || profile)
+ // notify thread to resume
+ jl_thread_resume(i, sig);
+ }
  jl_unlock_profile();
+ }
 #ifndef HAVE_MACH
  if (profile && running) {
 #if defined(HAVE_TIMER)

src/signals-win.c

@@ -91,7 +91,7 @@ void __cdecl crt_sig_handler(int sig, int num)
  RtlCaptureContext(&Context);
  if (sig == SIGILL)
  jl_show_sigill(&Context);
- jl_critical_error(sig, &Context);
+ jl_critical_error(sig, &Context, jl_get_current_task());
  raise(sig);
  }
 }
@@ -225,7 +225,8 @@ static BOOL WINAPI sigint_handler(DWORD wsig) //This needs winapi types to guara
 
 LONG WINAPI jl_exception_handler(struct _EXCEPTION_POINTERS *ExceptionInfo)
 {
- jl_ptls_t ptls = jl_current_task->ptls;
+ jl_task_t *ct = jl_current_task;
+ jl_ptls_t ptls = ct->ptls;
  if (ExceptionInfo->ExceptionRecord->ExceptionFlags == 0) {
  switch (ExceptionInfo->ExceptionRecord->ExceptionCode) {
  case EXCEPTION_INT_DIVIDE_BY_ZERO:
@@ -312,7 +313,7 @@ LONG WINAPI jl_exception_handler(struct _EXCEPTION_POINTERS *ExceptionInfo)
  jl_safe_printf(" at 0x%Ix -- ", (size_t)ExceptionInfo->ExceptionRecord->ExceptionAddress);
  jl_print_native_codeloc((uintptr_t)ExceptionInfo->ExceptionRecord->ExceptionAddress);
 
- jl_critical_error(0, ExceptionInfo->ContextRecord);
+ jl_critical_error(0, ExceptionInfo->ContextRecord, ct);
  static int recursion = 0;
  if (recursion++)
  exit(1);