sched/core: Allow putting thread_info into task_struct

If an arch opts in by setting CONFIG_THREAD_INFO_IN_TASK_STRUCT,
then thread_info is defined as a single 'u32 flags' and is the first
entry of task_struct.  thread_info::task is removed (it serves no
purpose if thread_info is embedded in task_struct), and
thread_info::cpu gets its own slot in task_struct.

This is heavily based on a patch written by Linus.

Originally-from: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jann Horn <jann@thejh.net>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/a0898196f0476195ca02713691a5037a14f2aac5.1473801993.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 7 insertions, 0 deletions

diff --git a/init/Kconfig b/init/Kconfig
index cac3f096050d..ec8d43894b02 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -26,6 +26,13 @@ config IRQ_WORK
 config BUILDTIME_EXTABLE_SORT
         bool
 
+config THREAD_INFO_IN_TASK
+        bool
+        help
+          Select this to move thread_info off the stack into task_struct.  To
+          make this work, an arch will need to remove all thread_info fields
+          except flags and fix any runtime bugs.
+
 menu "General setup"
 
 config BROKEN