ARM: 7473/1: deal with handlerless restarts without leaving the kernel

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/kernel/entry-common.S

@@ -54,7 +54,11 @@ work_pending:
 	mov	r0, sp				@ 'regs'
 	mov	r2, why				@ 'syscall'
 	bl	do_work_pending
-	b	no_work_pending
+	tst	r0, #1
+	beq	no_work_pending
+	ldmia	sp, {r0 - r6}			@ have to reload r0 - r6
+	b	local_restart			@ ... and off we go
+
 /*
  * "slow" syscall return path.  "why" tells us if this was a real syscall.
  */
@@ -396,6 +400,7 @@ ENTRY(vector_swi)
 	eor	scno, scno, #__NR_SYSCALL_BASE	@ check OS number
 #endif
 
+local_restart:
 	ldr	r10, [tsk, #TI_FLAGS]		@ check for syscall tracing
 	stmdb	sp!, {r4, r5}			@ push fifth and sixth args
 

arch/arm/kernel/signal.c

@@ -569,12 +569,13 @@ handle_signal(unsigned long sig, struct k_sigaction *ka,
  * the kernel can handle, and then we build all the user-level signal handling
  * stack-frames in one go after that.
  */
-static void do_signal(struct pt_regs *regs, int syscall)
+static int do_signal(struct pt_regs *regs, int syscall)
 {
 	unsigned int retval = 0, continue_addr = 0, restart_addr = 0;
 	struct k_sigaction ka;
 	siginfo_t info;
 	int signr;
+	int restart = 0;
 
 	/*
 	 * If we were from a system call, check for system call restarting...
@@ -589,10 +590,12 @@ static void do_signal(struct pt_regs *regs, int syscall)
 		 * debugger will see the already changed PSW.
 		 */
 		switch (retval) {
+		case -ERESTART_RESTARTBLOCK:
+			restart++;
 		case -ERESTARTNOHAND:
 		case -ERESTARTSYS:
 		case -ERESTARTNOINTR:
-		case -ERESTART_RESTARTBLOCK:
+			restart++;
 			regs->ARM_r0 = regs->ARM_ORIG_r0;
 			regs->ARM_pc = restart_addr;
 			break;
@@ -604,13 +607,15 @@ static void do_signal(struct pt_regs *regs, int syscall)
 	 * point the debugger may change all our registers ...
 	 */
 	signr = get_signal_to_deliver(&info, &ka, regs, NULL);
+	/*
+	 * Depending on the signal settings we may need to revert the
+	 * decision to restart the system call.  But skip this if a
+	 * debugger has chosen to restart at a different PC.
+	 */
+	if (regs->ARM_pc != restart_addr)
+		restart = 0;
 	if (signr > 0) {
-		/*
-		 * Depending on the signal settings we may need to revert the
-		 * decision to restart the system call.  But skip this if a
-		 * debugger has chosen to restart at a different PC.
-		 */
-		if (regs->ARM_pc == restart_addr) {
+		if (unlikely(restart)) {
 			if (retval == -ERESTARTNOHAND ||
 			    retval == -ERESTART_RESTARTBLOCK
 			    || (retval == -ERESTARTSYS
@@ -618,28 +623,23 @@ static void do_signal(struct pt_regs *regs, int syscall)
 				regs->ARM_r0 = -EINTR;
 				regs->ARM_pc = continue_addr;
 			}
-			clear_thread_flag(TIF_SYSCALL_RESTARTSYS);
 		}
 
 		handle_signal(signr, &ka, &info, regs);
-		return;
+		return 0;
 	}
 
-	if (syscall) {
-		/*
-		 * Handle restarting a different system call.  As above,
-		 * if a debugger has chosen to restart at a different PC,
-		 * ignore the restart.
-		 */
-		if (retval == -ERESTART_RESTARTBLOCK
-		    && regs->ARM_pc == restart_addr)
+	if (unlikely(restart)) {
+		if (restart > 1)
 			set_thread_flag(TIF_SYSCALL_RESTARTSYS);
+		regs->ARM_pc = continue_addr;
 	}
 
 	restore_saved_sigmask();
+	return restart;
 }
 
-asmlinkage void
+asmlinkage int
 do_work_pending(struct pt_regs *regs, unsigned int thread_flags, int syscall)
 {
 	do {
@@ -647,10 +647,17 @@ do_work_pending(struct pt_regs *regs, unsigned int thread_flags, int syscall)
 			schedule();
 		} else {
 			if (unlikely(!user_mode(regs)))
-				return;
+				return 0;
 			local_irq_enable();
 			if (thread_flags & _TIF_SIGPENDING) {
-				do_signal(regs, syscall);
+				if (unlikely(do_signal(regs, syscall))) {
+					/*
+					 * Restart without handlers.
+					 * Deal with it without leaving
+					 * the kernel space.
+					 */
+					return 1;
+				}
 				syscall = 0;
 			} else {
 				clear_thread_flag(TIF_NOTIFY_RESUME);
@@ -660,4 +667,5 @@ do_work_pending(struct pt_regs *regs, unsigned int thread_flags, int syscall)
 		local_irq_disable();
 		thread_flags = current_thread_info()->flags;
 	} while (thread_flags & _TIF_WORK_MASK);
+	return 0;
 }