x86: signal: sys_rt_sigreturn() should use set_current_blocked()

Normally sys_rt_sigreturn() restores the old current->blocked which was
changed by handle_signal(), and unblocking is always fine.

But the debugger or application itself can change frame->uc_sigmask and
thus we need set_current_blocked()->retarget_shared_pending().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Matt Fleming <matt.fleming@linux.intel.com>
Acked-by: Tejun Heo <tj@kernel.org>

arch/x86/kernel/signal.c

@@ -601,10 +601,7 @@ long sys_rt_sigreturn(struct pt_regs *regs)
 		goto badframe;
 
 	sigdelsetmask(&set, ~_BLOCKABLE);
-	spin_lock_irq(&current->sighand->siglock);
-	current->blocked = set;
-	recalc_sigpending();
-	spin_unlock_irq(&current->sighand->siglock);
+	set_current_blocked(&set);
 
 	if (restore_sigcontext(regs, &frame->uc.uc_mcontext, &ax))
 		goto badframe;