signal: add block_sigmask() for adding sigmask to current->blocked

Abstract the code sequence for adding a signal handler's sa_mask to
current->blocked because the sequence is identical for all architectures.
Furthermore, in the past some architectures actually got this code wrong,
so introduce a wrapper that all architectures can use.

Signed-off-by: Matt Fleming <matt.fleming@intel.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/x86/kernel/signal.c

@@ -682,7 +682,6 @@ static int
 handle_signal(unsigned long sig, siginfo_t *info, struct k_sigaction *ka,
 		struct pt_regs *regs)
 {
-	sigset_t blocked;
 	int ret;
 
 	/* Are we from a system call? */
@@ -733,10 +732,7 @@ handle_signal(unsigned long sig, siginfo_t *info, struct k_sigaction *ka,
 	 */
 	regs->flags &= ~X86_EFLAGS_TF;
 
-	sigorsets(&blocked, &current->blocked, &ka->sa.sa_mask);
-	if (!(ka->sa.sa_flags & SA_NODEFER))
-		sigaddset(&blocked, sig);
-	set_current_blocked(&blocked);
+	block_sigmask(ka, sig);
 
 	tracehook_signal_handler(sig, info, ka, regs,
 				 test_thread_flag(TIF_SINGLESTEP));

include/linux/signal.h

@@ -254,6 +254,7 @@ extern void set_current_blocked(const sigset_t *);
 extern int show_unhandled_signals;
 
 extern int get_signal_to_deliver(siginfo_t *info, struct k_sigaction *return_ka, struct pt_regs *regs, void *cookie);
+extern void block_sigmask(struct k_sigaction *ka, int signr);
 extern void exit_signals(struct task_struct *tsk);
 
 extern struct kmem_cache *sighand_cachep;

kernel/signal.c

@@ -2318,6 +2318,27 @@ relock:
 	return signr;
 }
 
+/**
+ * block_sigmask - add @ka's signal mask to current->blocked
+ * @ka: action for @signr
+ * @signr: signal that has been successfully delivered
+ *
+ * This function should be called when a signal has succesfully been
+ * delivered. It adds the mask of signals for @ka to current->blocked
+ * so that they are blocked during the execution of the signal
+ * handler. In addition, @signr will be blocked unless %SA_NODEFER is
+ * set in @ka->sa.sa_flags.
+ */
+void block_sigmask(struct k_sigaction *ka, int signr)
+{
+	sigset_t blocked;
+
+	sigorsets(&blocked, &current->blocked, &ka->sa.sa_mask);
+	if (!(ka->sa.sa_flags & SA_NODEFER))
+		sigaddset(&blocked, signr);
+	set_current_blocked(&blocked);
+}
+
 /*
  * It could be that complete_signal() picked us to notify about the
  * group-wide signal. Other threads should be notified now to take