On Wed, Dec 05, 2012 at 04:08:41PM +0000, James Hogan wrote:

+TBIRES tail_end(TBIRES State, unsigned long orig_syscall)
+{
+	struct pt_regs *regs = (struct pt_regs *)State.Sig.pCtx;
+	unsigned long flags;
+
+	if (user_mode(regs)) {
+		local_irq_enable();
+		/* This is actually a crucial little line - if the process
+		 * needs swapping out, then this is where it happens!
+		 */
+		if (need_resched())
+			schedule();
+
+		flags = current_thread_info()->flags;
+		if (flags & (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME)) {
+			/* Note the passing in of the original syscall number.
+			 * This is used for implementing signal restart.
+			 */
+			do_notify_resume(regs, orig_syscall != 0,
+					 orig_syscall, flags);

Owww....  So
	a) you can't get there with !user_mode(regs)
	b) you handle only one signal (what happens if you fail sigframe
allocation, BTW?  Sure, you get SIGSEGV delivered.  And don't handle it.)
	c) you read ->flags with no protection whatsoever.  It should be
done *before* you enable interrupts, and rechecked after you've done
do_notify_resume() and redisabled them.  The same for schedule().  It really
should be a loop; take a look at how it's done on arm and alpha - there that
loop is in C, not in asm glue.
	d) looks like your sigreturn is, indeed, broken.  It should *not* have
syscall restart logics triggered at all.