[PATCH] frv: fix signal handling

The attached patch makes FRV signal handling work properly:

 (1) After do_notify_resume() has been called, the work flags must be checked
     again (there may be another signal to deliver or the process might require
     rescheduling for instance).

 (2) After the signal frame is set up on the userspace stack, ptrace() should
     be given an opportunity to single-step into the signal handler.

 (3) The error state from setting up a signal frame should be passed back up
     the call chain.

 (4) The segfault handler shouldn't be preemptively reset in the arch if we
     fail to deliver a SEGV signal: force_sig() will take care of that.
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/frv/kernel/entry.S

@@ -1076,7 +1076,7 @@ __entry_work_notifysig:
 	LEDS		0x6410
 	ori.p		gr4,#0,gr8
 	call		do_notify_resume
-	bra		__entry_return_direct
+	bra		__entry_resume_userspace
 
 	# perform syscall entry tracing
 __syscall_trace_entry:

arch/frv/kernel/signal.c

@@ -297,7 +297,8 @@ static inline void __user *get_sigframe(struct k_sigaction *ka,
 /*
  *
  */
-static void setup_frame(int sig, struct k_sigaction *ka, sigset_t *set, struct pt_regs * regs)
+static int setup_frame(int sig, struct k_sigaction *ka, sigset_t *set,
+		       struct pt_regs *regs)
 {
 	struct sigframe __user *frame;
 	int rsig;
@@ -362,25 +363,29 @@ static void setup_frame(int sig, struct k_sigaction *ka, sigset_t *set, struct p
 
 	set_fs(USER_DS);
 
+	/* the tracer may want to single-step inside the handler */
+	if (test_thread_flag(TIF_SINGLESTEP))
+		ptrace_notify(SIGTRAP);
+
 #if DEBUG_SIG
 	printk("SIG deliver %d (%s:%d): sp=%p pc=%lx ra=%p\n",
-		sig, current->comm, current->pid, frame, regs->pc, frame->pretcode);
+	       sig, current->comm, current->pid, frame, regs->pc,
+	       frame->pretcode);
 #endif
 
-	return;
+	return 1;
 
 give_sigsegv:
-	if (sig == SIGSEGV)
-		ka->sa.sa_handler = SIG_DFL;
-
 	force_sig(SIGSEGV, current);
+	return 0;
+
 } /* end setup_frame() */
 
 /*****************************************************************************/
 /*
  *
  */
-static void setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
+static int setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
 			  sigset_t *set, struct pt_regs * regs)
 {
 	struct rt_sigframe __user *frame;
@@ -457,17 +462,21 @@ static void setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
 
 	set_fs(USER_DS);
 
+	/* the tracer may want to single-step inside the handler */
+	if (test_thread_flag(TIF_SINGLESTEP))
+		ptrace_notify(SIGTRAP);
+
 #if DEBUG_SIG
 	printk("SIG deliver %d (%s:%d): sp=%p pc=%lx ra=%p\n",
-		sig, current->comm, current->pid, frame, regs->pc, frame->pretcode);
+		sig, current->comm, current->pid, frame, regs->pc,
+	       frame->pretcode);
 #endif
 
-	return;
+	return 1;
 
 give_sigsegv:
-	if (sig == SIGSEGV)
-		ka->sa.sa_handler = SIG_DFL;
 	force_sig(SIGSEGV, current);
+	return 0;
 
 } /* end setup_rt_frame() */
 
@@ -475,10 +484,12 @@ static void setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
 /*
  * OK, we're invoking a handler
  */
-static void handle_signal(unsigned long sig, siginfo_t *info,
+static int handle_signal(unsigned long sig, siginfo_t *info,
 			 struct k_sigaction *ka, sigset_t *oldset,
 			 struct pt_regs *regs)
 {
+	int ret;
+
 	/* Are we from a system call? */
 	if (in_syscall(regs)) {
 		/* If so, check system call restarting.. */
@@ -493,6 +504,7 @@ static void handle_signal(unsigned long sig, siginfo_t *info,
 				regs->gr8 = -EINTR;
 				break;
 			}
+
 			/* fallthrough */
 		case -ERESTARTNOINTR:
 			regs->gr8 = regs->orig_gr8;
@@ -502,16 +514,22 @@ static void handle_signal(unsigned long sig, siginfo_t *info,
 
 	/* Set up the stack frame */
 	if (ka->sa.sa_flags & SA_SIGINFO)
-		setup_rt_frame(sig, ka, info, oldset, regs);
+		ret = setup_rt_frame(sig, ka, info, oldset, regs);
 	else
-		setup_frame(sig, ka, oldset, regs);
+		ret = setup_frame(sig, ka, oldset, regs);
 
+	if (ret) {
 		spin_lock_irq(&current->sighand->siglock);
-	sigorsets(&current->blocked, &current->blocked, &ka->sa.sa_mask);
+		sigorsets(&current->blocked, &current->blocked,
+			  &ka->sa.sa_mask);
 		if (!(ka->sa.sa_flags & SA_NODEFER))
 			sigaddset(&current->blocked, sig);
 		recalc_sigpending();
 		spin_unlock_irq(&current->sighand->siglock);
+	}
+
+	return ret;
+
 } /* end handle_signal() */
 
 /*****************************************************************************/
@@ -542,12 +560,10 @@ int do_signal(struct pt_regs *regs, sigset_t *oldset)
 		oldset = &current->blocked;
 
 	signr = get_signal_to_deliver(&info, &ka, regs, NULL);
-	if (signr > 0) {
-		handle_signal(signr, &info, &ka, oldset, regs);
-		return 1;
-	}
+	if (signr > 0)
+		return handle_signal(signr, &info, &ka, oldset, regs);
 
- no_signal:
+no_signal:
 	/* Did we come from a system call? */
 	if (regs->syscallno >= 0) {
 		/* Restart the system call - no handlers present */
@@ -565,6 +581,7 @@ int do_signal(struct pt_regs *regs, sigset_t *oldset)
 	}
 
 	return 0;
+
 } /* end do_signal() */
 
 /*****************************************************************************/