signals: kill block_all_signals() and unblock_all_signals()

It is hardly possible to enumerate all problems with block_all_signals()
and unblock_all_signals().  Just for example,

1. block_all_signals(SIGSTOP/etc) simply can't help if the caller is
   multithreaded. Another thread can dequeue the signal and force the
   group stop.

2. Even is the caller is single-threaded, it will "stop" anyway. It
   will not sleep, but it will spin in kernel space until SIGCONT or
   SIGKILL.

And a lot more. In short, this interface doesn't work at all, at least
the last 10+ years.

Daniel said:

  Yeah the only times I played around with the DRM_LOCK stuff was when
  old drivers accidentally deadlocked - my impression is that the entire
  DRM_LOCK thing was never really tested properly ;-) Hence I'm all for
  purging where this leaks out of the drm subsystem.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Dave Airlie <airlied@redhat.com>
Cc: Richard Weinberger <richard@nod.at>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/sched.h b/include/linux/sched.h
index eeb5066..923ec1a 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1570,9 +1570,7 @@
 
 	unsigned long sas_ss_sp;
 	size_t sas_ss_size;
-	int (*notifier)(void *priv);
-	void *notifier_data;
-	sigset_t *notifier_mask;
+
 	struct callback_head *task_works;
 
 	struct audit_context *audit_context;
@@ -2476,9 +2474,6 @@
 	return ret;
 }
 
-extern void block_all_signals(int (*notifier)(void *priv), void *priv,
-			      sigset_t *mask);
-extern void unblock_all_signals(void);
 extern void release_task(struct task_struct * p);
 extern int send_sig_info(int, struct siginfo *, struct task_struct *);
 extern int force_sigsegv(int, struct task_struct *);