this is a fragile piece of the ptrace code, the code relies on a single wakeup...

this is a fragile piece of the ptrace code, the code relies on a single wakeup coming from the parent.
This fix is necessery after the preempt_schedule() cleanups, it unbreaks 'strace strace ...'.

arch/i386/kernel/ptrace.c

@@ -455,9 +455,11 @@ void do_syscall_trace(struct pt_regs *regs, int entryexit)
 	   between a syscall stop and SIGTRAP delivery */
 	current->exit_code = SIGTRAP | ((current->ptrace & PT_TRACESYSGOOD)
 					? 0x80 : 0);
+	preempt_disable();
 	current->state = TASK_STOPPED;
 	notify_parent(current, SIGCHLD);
 	schedule();
+	preempt_enable();
 	/*
 	 * this isn't the same as continuing with a signal, but it will do
 	 * for normal use.  strace only continues with a signal if the

arch/i386/kernel/signal.c

@@ -610,9 +610,11 @@ int do_signal(struct pt_regs *regs, sigset_t *oldset)
 		if ((current->ptrace & PT_PTRACED) && signr != SIGKILL) {
 			/* Let the debugger run.  */
 			current->exit_code = signr;
+			preempt_disable();
 			current->state = TASK_STOPPED;
 			notify_parent(current, SIGCHLD);
 			schedule();
+			preempt_enable();
 
 			/* We're back.  Did the debugger cancel the sig?  */
 			if (!(signr = current->exit_code))
@@ -667,12 +669,14 @@ int do_signal(struct pt_regs *regs, sigset_t *oldset)
 
 			case SIGSTOP: {
 				struct signal_struct *sig;
-				current->state = TASK_STOPPED;
 				current->exit_code = signr;
 				sig = current->p_pptr->sig;
+				preempt_disable();
+				current->state = TASK_STOPPED;
 				if (sig && !(sig->action[SIGCHLD-1].sa.sa_flags & SA_NOCLDSTOP))
 					notify_parent(current, SIGCHLD);
 				schedule();
+				preempt_enable();
 				continue;
 			}