arm64: update die handler from ARM / x86

Commit 02df19b4 ("ARM:
7424/1: update die handler from x86") refactored the ARM
die() logic to avoid a deadlock if a kernel oops happens
while holding a spinlock that may also be used in an IRQ
handler. Refactor the ARM64 die() handler in a similar way,
to avoid similar deadlocks, which would have otherwise
prevented the kernel from printing the full panic output
and properly completing the panic() path.

Change-Id: I217a8d719f64b54467fa88a583d83f72193d7580
Signed-off-by: Stepan Moskovchenko <stepanm@codeaurora.org>

arch/arm64/kernel/traps.c

@@ -214,44 +214,76 @@ static int __die(const char *str, int err, struct thread_info *thread,
 	return ret;
 }
 
-static DEFINE_RAW_SPINLOCK(die_lock);
+static arch_spinlock_t die_lock = __ARCH_SPIN_LOCK_UNLOCKED;
+static int die_owner = -1;
+static unsigned int die_nest_count;
 
-/*
- * This function is protected against re-entrancy.
- */
-void die(const char *str, struct pt_regs *regs, int err)
+static unsigned long oops_begin(void)
 {
-	struct thread_info *thread = current_thread_info();
-	int ret;
-	enum bug_trap_type bug_type = BUG_TRAP_TYPE_NONE;
+	int cpu;
+	unsigned long flags;
 
 	oops_enter();
 
-	raw_spin_lock_irq(&die_lock);
+	/* racy, but better than risking deadlock. */
+	raw_local_irq_save(flags);
+	cpu = smp_processor_id();
+	if (!arch_spin_trylock(&die_lock)) {
+		if (cpu == die_owner)
+			/* nested oops. should stop eventually */;
+		else
+			arch_spin_lock(&die_lock);
+	}
+	die_nest_count++;
+	die_owner = cpu;
 	console_verbose();
 	bust_spinlocks(1);
-	if (!user_mode(regs))
-		bug_type = report_bug(regs->pc, regs);
-	if (bug_type != BUG_TRAP_TYPE_NONE)
-		str = "Oops - BUG";
-	ret = __die(str, err, thread, regs);
+	return flags;
+}
 
-	if (regs && kexec_should_crash(thread->task))
+static void oops_end(unsigned long flags, struct pt_regs *regs, int notify)
+{
+	if (regs && kexec_should_crash(current))
 		crash_kexec(regs);
 
 	bust_spinlocks(0);
+	die_owner = -1;
 	add_taint(TAINT_DIE, LOCKDEP_NOW_UNRELIABLE);
-	raw_spin_unlock_irq(&die_lock);
+	die_nest_count--;
+	if (!die_nest_count)
+		/* Nest count reaches zero, release the lock. */
+		arch_spin_unlock(&die_lock);
+	raw_local_irq_restore(flags);
 	oops_exit();
 
 	if (in_interrupt())
 		panic("Fatal exception in interrupt");
 	if (panic_on_oops)
 		panic("Fatal exception");
-	if (ret != NOTIFY_STOP)
+	if (notify != NOTIFY_STOP)
 		do_exit(SIGSEGV);
 }
 
+/*
+ * This function is protected against re-entrancy.
+ */
+void die(const char *str, struct pt_regs *regs, int err)
+{
+	struct thread_info *thread = current_thread_info();
+	enum bug_trap_type bug_type = BUG_TRAP_TYPE_NONE;
+	unsigned long flags = oops_begin();
+	int ret;
+
+	if (!user_mode(regs))
+		bug_type = report_bug(regs->pc, regs);
+	if (bug_type != BUG_TRAP_TYPE_NONE)
+		str = "Oops - BUG";
+
+	ret = __die(str, err, thread, regs);
+
+	oops_end(flags, regs, ret);
+}
+
 void arm64_notify_die(const char *str, struct pt_regs *regs,
 		      struct siginfo *info, int err)
 {