sparc64: Fix syscall restart, for real...

The change I put into copy_thread() just papered over the real
problem.

When we are looking to see if we should do a syscall restart, when
deliverying a signal, we should only interpret the syscall return
value as an error if the carry condition code(s) are set.

Otherwise it's a success return.

Also, sigreturn paths should do a pt_regs_clear_trap_type().

It turns out that doing a syscall restart when returning from a fork()
does and should happen, from time to time.  Even if copy_thread()
returns success, copy_process() can still unwind and signal
-ERESTARTNOINTR in the parent.

Signed-off-by: David S. Miller <davem@davemloft.net>

arch/sparc64/kernel/process.c

@@ -591,12 +591,6 @@ int copy_thread(int nr, unsigned long clone_flags, unsigned long sp,
 	if (clone_flags & CLONE_SETTLS)
 		t->kregs->u_regs[UREG_G7] = regs->u_regs[UREG_I3];
 
-	/* We do not want to accidently trigger system call restart
-	 * handling in the new thread.  Therefore, clear out the trap
-	 * type, which will make pt_regs_regs_is_syscall() return false.
-	 */
-	pt_regs_clear_trap_type(t->kregs);
-
 	return 0;
 }
 

arch/sparc64/kernel/signal.c

@@ -332,6 +332,9 @@ void do_rt_sigreturn(struct pt_regs *regs)
 	regs->tpc = tpc;
 	regs->tnpc = tnpc;
 
+	/* Prevent syscall restart.  */
+	pt_regs_clear_trap_type(regs);
+
 	sigdelsetmask(&set, ~_BLOCKABLE);
 	spin_lock_irq(&current->sighand->siglock);
 	current->blocked = set;
@@ -515,7 +518,8 @@ static void do_signal(struct pt_regs *regs, unsigned long orig_i0)
 	siginfo_t info;
 	int signr;
 
-	if (pt_regs_is_syscall(regs)) {
+	if (pt_regs_is_syscall(regs) &&
+	    (regs->tstate & (TSTATE_XCARRY | TSTATE_ICARRY))) {
 		pt_regs_clear_trap_type(regs);
 		cookie.restart_syscall = 1;
 	} else

arch/sparc64/kernel/signal32.c

@@ -268,6 +268,9 @@ void do_sigreturn32(struct pt_regs *regs)
 	regs->tstate &= ~(TSTATE_ICC|TSTATE_XCC);
 	regs->tstate |= psr_to_tstate_icc(psr);
 
+	/* Prevent syscall restart.  */
+	pt_regs_clear_trap_type(regs);
+
 	err |= __get_user(fpu_save, &sf->fpu_save);
 	if (fpu_save)
 		err |= restore_fpu_state32(regs, &sf->fpu_state);
@@ -351,6 +354,9 @@ asmlinkage void do_rt_sigreturn32(struct pt_regs *regs)
 	regs->tstate &= ~(TSTATE_ICC|TSTATE_XCC);
 	regs->tstate |= psr_to_tstate_icc(psr);
 
+	/* Prevent syscall restart.  */
+	pt_regs_clear_trap_type(regs);
+
 	err |= __get_user(fpu_save, &sf->fpu_save);
 	if (fpu_save)
 		err |= restore_fpu_state32(regs, &sf->fpu_state);