[MIPS] Avoid double signal restarting.

In entry.S resume_userspace ... jal do_notify_resume form a loop through
which the kernel will iterate as long as work is pending.  If we
iterate through this loop more than once with no signal pending for at
least one but the last iteration we will take do the syscall restarting
multiple times resulting in a syscall return prior to the the syscall
instruction in userspace.  This may happen when debugging a multithreaded
program.

Debugging and original fix by Maciej; extended to other ABIs by me.

Signed-off-by: Maciej W. Rozycki <macro@mips.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kernel/irixsig.c

@@ -224,6 +224,7 @@ void do_irix_signal(struct pt_regs *regs)
 			regs->regs[7] = regs->regs[26];
 			regs->cp0_epc -= 4;
 		}
+		regs->regs[0] = 0;	/* Don't deal with this again.  */
 	}
 
 	/*

arch/mips/kernel/signal.c

@@ -429,7 +429,6 @@ void do_signal(struct pt_regs *regs)
 	else
 		oldset = &current->blocked;
 
-
 	signr = get_signal_to_deliver(&info, &ka, regs, NULL);
 	if (signr > 0) {
 		/* Whee!  Actually deliver the signal.  */
@@ -464,6 +463,7 @@ void do_signal(struct pt_regs *regs)
 			regs->regs[7] = regs->regs[26];
 			regs->cp0_epc -= 4;
 		}
+		regs->regs[0] = 0;	/* Don't deal with this again.  */
 	}
 
 	/*

arch/mips/kernel/signal32.c

@@ -854,6 +854,7 @@ void do_signal32(struct pt_regs *regs)
 			regs->regs[7] = regs->regs[26];
 			regs->cp0_epc -= 4;
 		}
+		regs->regs[0] = 0;	/* Don't deal with this again.  */
 	}
 
 	/*