[PATCH V2] sched: Update the THREAD_INFO_IN_TASK description

[Huacai Chen]

When commit c65eacbe290b81 ("sched/core: Allow putting thread_info into
task_struct") introduces THREAD_INFO_IN_TASK in 4.9, the only supported
architecture is x86 and thread_info only has a flags field. The Kconfig
description said thread_info should only has the flags field but didn't
explain the reason.

When commit c02433dd6de32f ("arm64: split thread_info from task stack")
introduces THREAD_INFO_IN_TASK for arm64 in 4.10, its thread_info has
more fields than a single flags, and arm64 works well.

Then commit 37a8f7c38339b2 ("x86/asm: Move 'status' from thread_struct
to thread_info") adds status back to thread_info for x86 in 4.16, and
x86 still works well.

After that, risc-v, powerpc and many other architectures all introduce
THREAD_INFO_IN_TASK and their thread_info have more fields rather than
a single flags field, of course they also work well.

I don't know the exact reason of the original description, but obviously
it is wrong and misleading, so I update it, let LoongArch and some other
architectures easier to support THREAD_INFO_IN_TASK.

Also improve the try_get_task_stack() and put_task_stack() description.

Signed-off-by: Huacai Chen <chenhuacai@xxxxxxxxxxx>
---
 init/Kconfig | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/init/Kconfig b/init/Kconfig
index 2937c4d308ae..a9466879d553 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -207,11 +207,12 @@ 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.
+	  make this work, an arch will need to remove the task_struct pointer
+	  field from thread_info and fix any runtime bugs.
 
 	  One subtle change that will be needed is to use try_get_task_stack()
-	  and put_task_stack() in save_thread_stack_tsk() and get_wchan().
+	  and put_task_stack() in save_thread_stack_tsk(), get_wchan() and any
+	  other stacktrace functions.
 
 menu "General setup"
 
-- 
2.52.0