sched/headers: Move task_struct::signal and task_struct::sighand type…

…s and accessors into <linux/sched/signal.h>

task_struct::signal and task_struct::sighand are pointers, which would normally make it
straightforward to not define those types in sched.h.

That is not so, because the types are accompanied by a myriad of APIs (macros and inline
functions) that dereference them.

Split the types and the APIs out of sched.h and move them into a new header, <linux/sched/signal.h>.

With this change sched.h does not know about 'struct signal' and 'struct sighand' anymore,
trying to put accessors into sched.h as a test fails the following way:

  ./include/linux/sched.h: In function ‘test_signal_types’:
  ./include/linux/sched.h:2461:18: error: dereferencing pointer to incomplete type ‘struct signal_struct’
                    ^

This reduces the size and complexity of sched.h significantly.

Update all headers and .c code that relied on getting the signal handling
functionality from <linux/sched.h> to include <linux/sched/signal.h>.

The list of affected files in the preparatory patch was partly generated by
grepping for the APIs, and partly by doing coverage build testing, both
all[yes|mod|def|no]config builds on 64-bit and 32-bit x86, and an array of
cross-architecture builds.

Nevertheless some (trivial) build breakage is still expected related to rare
Kconfig combinations and in-flight patches to various kernel code, but most
of it should be handled by this patch.

Acked-by: Linus Torvalds <[email protected]>
Cc: Mike Galbraith <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Signed-off-by: Ingo Molnar <[email protected]>

arch/arm/nwfpe/fpmodule.c

@@ -31,7 +31,7 @@
 #include <linux/types.h>
 #include <linux/kernel.h>
 #include <linux/signal.h>
-#include <linux/sched.h>
+#include <linux/sched/signal.h>
 #include <linux/init.h>
 
 #include <asm/thread_notify.h>

arch/sh/kernel/cpu/sh4/fpu.c

@@ -10,8 +10,7 @@
  *
  * FIXME! These routines have not been tested for big endian case.
  */
-#include <linux/sched.h>
-#include <linux/signal.h>
+#include <linux/sched/signal.h>
 #include <linux/io.h>
 #include <cpu/fpu.h>
 #include <asm/processor.h>

drivers/net/tap.c

@@ -8,7 +8,7 @@
 #include <linux/module.h>
 #include <linux/skbuff.h>
 #include <linux/cache.h>
-#include <linux/sched.h>
+#include <linux/sched/signal.h>
 #include <linux/types.h>
 #include <linux/slab.h>
 #include <linux/wait.h>