[RFC][PATCH 0/2] Add is_user_thread() and is_kernel_thread() helper functions

[Steven Rostedt]

While working on the deferred stacktrace code, Peter Zijlstra told
me to use task->flags & PF_KTHREAD instead of checking task->mm for NULL.
This seemed reasonable, but while working on it, as there were several
places that check if the task is a kernel thread and other places that
check if the task is a user space thread I found it a bit confusing
when looking at both:

	if (task->flags & PF_KTHREAD)
and
	if (!(task->flags & PF_KTHREAD))

Where I mixed them up sometimes, and checked for a user space thread when I
really wanted to check for a kernel thread. I found these mistakes before
sending out my patches, but going back and reviewing the code, I always had
to stop and spend a few unnecessary seconds making sure the check was
testing that flag correctly.

To make this a bit more obvious, I introduced two helper functions:

	is_user_thread(task)
	is_kernel_thread(task)

which simply test the flag for you. Thus, seeing:

	if (is_user_thread(task))
or
	if (is_kernel_thread(task))

it was very obvious to which test you wanted to make.

I then created a coccinelle script to change all the checks throughout the
kernel to use one of these macros.

      $ cat kthread.cocci
      @@
      identifier task;
      @@
      -     !(task->flags & PF_KTHREAD)
      +     is_user_thread(task)
      @@
      identifier task;
      @@
      -     (task->flags & PF_KTHREAD) == 0
      +     is_user_thread(task)
      @@
      identifier task;
      @@
      -     (task->flags & PF_KTHREAD) != 0
      +     is_kernel_thread(task)
      @@
      identifier task;
      @@
      -     task->flags & PF_KTHREAD
      +     is_kernel_thread(task)
    
      $ spatch --dir --include-headers kthread.cocci . > /tmp/t.patch
      $ patch -p1 < /tmp/t.patch

Make sure to undo the conversion of the helper functions themselves!
        
      $ git show include/linux/sched.h | patch -p1 -R

It did modify the tools/sched_ext code, and I'm not sure if that's OK
or not. Does it still use the sched.h header? If so, it should be fine.
But if it is an issue, I can undo the changes to tools as well.


Steven Rostedt (2):
      kthread: Add is_user_thread() and is_kernel_thread() helper functions
      treewide: Have the task->flags & PF_KTHREAD check use the helper functions

----
 arch/arm/mm/init.c                         |  2 +-
 arch/arm64/include/asm/uaccess.h           |  2 +-
 arch/arm64/kernel/process.c                |  2 +-
 arch/arm64/kernel/proton-pack.c            |  2 +-
 arch/mips/kernel/process.c                 |  2 +-
 arch/powerpc/kernel/process.c              |  2 +-
 arch/powerpc/kernel/stacktrace.c           |  2 +-
 arch/x86/kernel/fpu/core.c                 |  2 +-
 arch/x86/kernel/process.c                  |  2 +-
 block/blk-cgroup.c                         |  2 +-
 drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h |  2 +-
 drivers/md/dm-vdo/logger.c                 |  2 +-
 drivers/tty/sysrq.c                        |  2 +-
 fs/bcachefs/clock.c                        |  2 +-
 fs/bcachefs/journal_reclaim.c              |  2 +-
 fs/bcachefs/move.c                         |  6 +++---
 fs/exec.c                                  |  2 +-
 fs/file_table.c                            |  2 +-
 fs/namespace.c                             |  2 +-
 fs/proc/array.c                            |  4 ++--
 fs/proc/base.c                             |  6 +++---
 include/linux/sched.h                      | 10 ++++++++++
 io_uring/io_uring.c                        |  2 +-
 kernel/cgroup/cgroup.c                     |  6 +++---
 kernel/cgroup/freezer.c                    |  4 ++--
 kernel/events/core.c                       |  2 +-
 kernel/exit.c                              |  2 +-
 kernel/fork.c                              |  6 +++---
 kernel/freezer.c                           |  4 ++--
 kernel/futex/pi.c                          |  2 +-
 kernel/kthread.c                           | 12 ++++++------
 kernel/livepatch/transition.c              |  2 +-
 kernel/power/process.c                     |  2 +-
 kernel/sched/core.c                        |  6 +++---
 kernel/sched/idle.c                        |  2 +-
 kernel/sched/sched.h                       |  4 ++--
 kernel/signal.c                            |  4 ++--
 kernel/stacktrace.c                        |  2 +-
 lib/is_single_threaded.c                   |  2 +-
 mm/memcontrol.c                            |  2 +-
 mm/oom_kill.c                              |  4 ++--
 mm/page_alloc.c                            |  2 +-
 mm/vmscan.c                                |  2 +-
 security/keys/request_key.c                |  2 +-
 security/smack/smack_access.c              |  2 +-
 security/smack/smack_lsm.c                 |  4 ++--
 security/tomoyo/network.c                  |  2 +-
 security/yama/yama_lsm.c                   |  2 +-
 tools/sched_ext/scx_central.bpf.c          |  2 +-
 tools/sched_ext/scx_flatcg.bpf.c           |  2 +-
 tools/sched_ext/scx_qmap.bpf.c             |  2 +-
 51 files changed, 82 insertions(+), 72 deletions(-)