runtime: make sure halt() is not called before abort() message is pri…

…nted

Concurrent abort() call will call osv::halt() immediately which may
result in a halting NMI being delivered to the CPU which is in the
middle of printing the abort message. This can lead to silent aborts
with no message on the screen. To make debugging easier, let the first
aborter call osv::halt(), others will just spin and wait for the
leader to halt all CPUs.

Signed-off-by: Tomasz Grabiec <tgrabiec@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>

runtime.cc

@@ -103,39 +103,43 @@ static void print_backtrace(void)
     }
 }
 
-static bool already_aborted = false;
+static std::atomic<bool> aborting { false };
+
 void abort()
 {
     abort("Aborted\n");
 }
 
 void abort(const char *fmt, ...)
 {
-    if (!already_aborted) {
-        arch::irq_disable();
-        already_aborted = true;
-
-        static char msg[1024];
-        va_list ap;
-
-        va_start(ap, fmt);
-        vsnprintf(msg, sizeof(msg), fmt, ap);
-        va_end(ap);
-
-        debug_early(msg);
-        // backtrace requires threads to be available, and also
-        // ELF s_program to be initialized. Since s_program happens
-        // later, this check is enough to ensure a minimal fallback
-        // functionality even early on.
-        if (elf::get_program() != nullptr) {
-            print_backtrace();
-        } else {
-            debug_early("Halting.\n");
-        }
+    bool expected = false;
+    if (!aborting.compare_exchange_strong(expected, true)) {
+        do {} while (true);
+    }
+
+    arch::irq_disable();
+
+    static char msg[1024];
+    va_list ap;
+
+    va_start(ap, fmt);
+    vsnprintf(msg, sizeof(msg), fmt, ap);
+    va_end(ap);
+
+    debug_early(msg);
+    // backtrace requires threads to be available, and also
+    // ELF s_program to be initialized. Since s_program happens
+    // later, this check is enough to ensure a minimal fallback
+    // functionality even early on.
+    if (elf::get_program() != nullptr) {
+        print_backtrace();
+    } else {
+        debug_early("Halting.\n");
+    }
 #ifndef AARCH64_PORT_STUB
-        panic::pvpanic::panicked();
+    panic::pvpanic::panicked();
 #endif /* !AARCH64_PORT_STUB */
-    }
+
     osv::halt();
 }