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

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

Author: vtjnash

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);