um: use set_current_blocked() and block_sigmask()

As described in commit e6fa16ab9c1e ("signal: sigprocmask() should do
retarget_shared_pending()") the modification of current->blocked is
incorrect as we need to check whether the signal we're about to block is
pending in the shared queue.

Also, use the new helper function introduced in commit 5e6292c0f28f
("signal: add block_sigmask() for adding sigmask to current->blocked")
which centralises the code for updating current->blocked after
successfully delivering a signal and reduces the amount of duplicate
code across architectures. In the past some architectures got this code
wrong, so using this helper function should stop that from happening
again.

Acked-by: Oleg Nesterov <[e-mail]>
Cc: Richard Weinberger <[e-mail]>
Signed-off-by: Matt Fleming <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/um/kernel/signal.c

···
 
 	if (err)
 		force_sigsegv(signr, current);
-	else {
-		spin_lock_irq(&current->sighand->siglock);
-		sigorsets(&current->blocked, &current->blocked,
-			  &ka->sa.sa_mask);
-		if (!(ka->sa.sa_flags & SA_NODEFER))
-			sigaddset(&current->blocked, signr);
-		recalc_sigpending();
-		spin_unlock_irq(&current->sighand->siglock);
-	}
+	else
+		block_sigmask(ka, signr);
 
 	return err;
 }
···
  */
 long sys_sigsuspend(int history0, int history1, old_sigset_t mask)
 {
+	sigset_t blocked;
+
 	mask &= _BLOCKABLE;
-	spin_lock_irq(&current->sighand->siglock);
-	current->saved_sigmask = current->blocked;
-	siginitset(&current->blocked, mask);
-	recalc_sigpending();
-	spin_unlock_irq(&current->sighand->siglock);
+	siginitset(&blocked, mask);
+	set_current_blocked(&blocked);
 
 	current->state = TASK_INTERRUPTIBLE;
 	schedule();