kgdb: fix several kgdb regressions

kgdb core fixes:
- Check to see that mm->mmap_cache is not null before calling
  flush_cache_range(), else on arch=ARM it will cause a fatal
  fault.

- Breakpoints should only be restored if they are in the BP_ACTIVE
  state.

- Fix a typo in comments to "kgdb_register_io_module"

x86 kgdb fixes:
- Fix the x86 arch handler such that on a kill or detach that the
  appropriate cleanup on the single stepping flags gets run.

- Add in the DIE_NMIWATCHDOG call for x86_64

- Touch the nmi watchdog before returning the system to normal
  operation after performing any kind of kgdb operation, else
  the possibility exists to trigger the watchdog.
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/kgdb.c

@@ -370,6 +370,8 @@ int kgdb_arch_handle_exception(int e_vector, int signo, int err_code,
 		ptr = &remcomInBuffer[1];
 		if (kgdb_hex2long(&ptr, &addr))
 			linux_regs->ip = addr;
+	case 'D':
+	case 'k':
 		newPC = linux_regs->ip;
 
 		/* clear the trace bit */
@@ -480,6 +482,8 @@ static int __kgdb_notify(struct die_args *args, unsigned long cmd)
 	if (kgdb_handle_exception(args->trapnr, args->signr, args->err, regs))
 		return NOTIFY_DONE;
 
+	/* Must touch watchdog before return to normal operation */
+	touch_nmi_watchdog();
 	return NOTIFY_STOP;
 }
 

arch/x86/kernel/traps_64.c

@@ -600,8 +600,13 @@ void die(const char * str, struct pt_regs * regs, long err)
 
 void __kprobes die_nmi(char *str, struct pt_regs *regs, int do_panic)
 {
-	unsigned long flags = oops_begin();
+	unsigned long flags;
+
+	if (notify_die(DIE_NMIWATCHDOG, str, regs, 0, 2, SIGINT) ==
+	    NOTIFY_STOP)
+		return;
 
+	flags = oops_begin();
 	/*
 	 * We are in trouble anyway, lets at least try
 	 * to get a message out.

kernel/kgdb.c

@@ -600,7 +600,7 @@ static void kgdb_flush_swbreak_addr(unsigned long addr)
 	if (!CACHE_FLUSH_IS_SAFE)
 		return;
 
-	if (current->mm) {
+	if (current->mm && current->mm->mmap_cache) {
 		flush_cache_range(current->mm->mmap_cache,
 				  addr, addr + BREAK_INSTR_SIZE);
 	} else {
@@ -729,14 +729,16 @@ int remove_all_break(void)
 
 	/* Clear memory breakpoints. */
 	for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
-		if (kgdb_break[i].state != BP_SET)
-			continue;
+		if (kgdb_break[i].state != BP_ACTIVE)
+			goto setundefined;
 		addr = kgdb_break[i].bpt_addr;
 		error = kgdb_arch_remove_breakpoint(addr,
 				kgdb_break[i].saved_instr);
 		if (error)
-			return error;
-		kgdb_break[i].state = BP_REMOVED;
+			printk(KERN_ERR "KGDB: breakpoint remove failed: %lx\n",
+			   addr);
+setundefined:
+		kgdb_break[i].state = BP_UNDEFINED;
 	}
 
 	/* Clear hardware breakpoints. */
@@ -1605,7 +1607,7 @@ static void kgdb_initial_breakpoint(void)
 }
 
 /**
- *	kkgdb_register_io_module - register KGDB IO module
+ *	kgdb_register_io_module - register KGDB IO module
  *	@new_kgdb_io_ops: the io ops vector
  *
  *	Register it with the KGDB core.