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

[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(-)

[RFC][PATCH 1/2] kthread: Add is_user_thread() and is_kernel_thread() helper functions

[Steven Rostedt]

From: Steven Rostedt <rostedt@goodmis.org>

In order to know if a task is a user thread or a kernel thread it is
recommended to test the task flags for PF_KTHREAD. The old way was to
check if the task mm pointer is NULL.

It is an easy mistake to not test the flag correctly, as:

	if (!(task->flag & PF_KTHREAD))

Is not immediately obvious that it's testing for a user thread.

Add helper functions:

  is_user_thread()
  is_kernel_thread()

that can make seeing what is being tested for much more obvious:

	if (is_user_thread(task))

Link: https://lore.kernel.org/all/20250425133416.63d3e3b8@gandalf.local.home/

Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 include/linux/sched.h | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index f96ac1982893..823f38b0fd3e 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1785,6 +1785,16 @@ static __always_inline bool is_percpu_thread(void)
 #endif
 }
 
+static __always_inline bool is_user_thread(struct task_struct *task)
+{
+	return !(task->flags & PF_KTHREAD);
+}
+
+static __always_inline bool is_kernel_thread(struct task_struct *task)
+{
+	return task->flags & PF_KTHREAD;
+}
+
 /* Per-process atomic flags. */
 #define PFA_NO_NEW_PRIVS		0	/* May not gain new privileges. */
 #define PFA_SPREAD_PAGE			1	/* Spread page cache over cpuset */
-- 
2.47.2

Re: [RFC][PATCH 1/2] kthread: Add is_user_thread() and is_kernel_thread() helper functions

[Kees Cook]

On Fri, Apr 25, 2025 at 04:41:21PM -0400, Steven Rostedt wrote:
> From: Steven Rostedt <rostedt@goodmis.org>
> 
> In order to know if a task is a user thread or a kernel thread it is
> recommended to test the task flags for PF_KTHREAD. The old way was to
> check if the task mm pointer is NULL.
> 
> It is an easy mistake to not test the flag correctly, as:
> 
> 	if (!(task->flag & PF_KTHREAD))
> 
> Is not immediately obvious that it's testing for a user thread.
> 
> Add helper functions:
> 
>   is_user_thread()
>   is_kernel_thread()
> 
> that can make seeing what is being tested for much more obvious:
> 
> 	if (is_user_thread(task))
> 
> Link: https://lore.kernel.org/all/20250425133416.63d3e3b8@gandalf.local.home/
> 
> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
> ---
>  include/linux/sched.h | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index f96ac1982893..823f38b0fd3e 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1785,6 +1785,16 @@ static __always_inline bool is_percpu_thread(void)
>  #endif
>  }
>  
> +static __always_inline bool is_user_thread(struct task_struct *task)
> +{
> +	return !(task->flags & PF_KTHREAD);
> +}
> +
> +static __always_inline bool is_kernel_thread(struct task_struct *task)
> +{
> +	return task->flags & PF_KTHREAD;

nit: maybe do explicit type conversion:

	return !!(task->flags & PF_KTHREAD);

but that's just a style issue, really.

Reviewed-by: Kees Cook <kees@kernel.org>

Thank you for not using current->mm -- KUnit, live patching, etc, all
use current->mm but are kthreads. :)

-- 
Kees Cook

Re: [RFC][PATCH 1/2] kthread: Add is_user_thread() and is_kernel_thread() helper functions

[Steven Rostedt]

On Fri, 25 Apr 2025 16:03:16 -0700
Kees Cook <kees@kernel.org> wrote:

> > +static __always_inline bool is_kernel_thread(struct task_struct *task)
> > +{
> > +	return task->flags & PF_KTHREAD;  
> 
> nit: maybe do explicit type conversion:
> 
> 	return !!(task->flags & PF_KTHREAD);
> 
> but that's just a style issue, really.

I may use Boris's suggestion (which I thought of doing originally too)
and have this return:

	return !is_user_thread(task);


> 
> Reviewed-by: Kees Cook <kees@kernel.org>

Thanks.

> 
> Thank you for not using current->mm -- KUnit, live patching, etc, all
> use current->mm but are kthreads. :)

Yeah, Peter was stressing this.

-- Steve

Re: [RFC][PATCH 1/2] kthread: Add is_user_thread() and is_kernel_thread() helper functions

[Borislav Petkov]

On April 25, 2025 11:41:21 PM GMT+03:00, Steven Rostedt <rostedt@goodmis.org> wrote:
>From: Steven Rostedt <rostedt@goodmis.org>
>
>In order to know if a task is a user thread or a kernel thread it is
>recommended to test the task flags for PF_KTHREAD. The old way was to
>check if the task mm pointer is NULL.
>
>It is an easy mistake to not test the flag correctly, as:
>
>	if (!(task->flag & PF_KTHREAD))
>
>Is not immediately obvious that it's testing for a user thread.
>
>Add helper functions:
>
>  is_user_thread()
>  is_kernel_thread()
>
>that can make seeing what is being tested for much more obvious:
>
>	if (is_user_thread(task))
>
>Link: https://lore.kernel.org/all/20250425133416.63d3e3b8@gandalf.local.home/
>
>Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
>---
> include/linux/sched.h | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
>diff --git a/include/linux/sched.h b/include/linux/sched.h
>index f96ac1982893..823f38b0fd3e 100644
>--- a/include/linux/sched.h
>+++ b/include/linux/sched.h
>@@ -1785,6 +1785,16 @@ static __always_inline bool is_percpu_thread(void)
> #endif
> }
> 
>+static __always_inline bool is_user_thread(struct task_struct *task)
>+{
>+	return !(task->flags & PF_KTHREAD);
>+}
>+
>+static __always_inline bool is_kernel_thread(struct task_struct *task)
>+{
>+	return task->flags & PF_KTHREAD;

return !is_user_thread(task);

or the other way around. 

🙂

-- 
Sent from a small device: formatting sucks and brevity is inevitable.

Re: [RFC][PATCH 1/2] kthread: Add is_user_thread() and is_kernel_thread() helper functions

[Steven Rostedt]

On Sat, 26 Apr 2025 14:08:46 +0300
Borislav Petkov <bp@alien8.de> wrote:

> >+static __always_inline bool is_kernel_thread(struct task_struct *task)
> >+{
> >+	return task->flags & PF_KTHREAD;  
> 
> return !is_user_thread(task);
> 
> or the other way around. 

Yeah, I thought about doing that but decided against it.

As Kees mentioned to use !!, I think using the !is_user_thread() is a
better approach.

-- Steve

[RFC][PATCH 2/2] treewide: Have the task->flags & PF_KTHREAD check use the helper functions

[Steven Rostedt]

From: Steven Rostedt <rostedt@goodmis.org>

Getting the check if a task is a kernel thread or a user thread can be
error prone as it's not easy to see the difference.

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

Is not immediately obvious that it's checking for a user thread.

	if (is_user_thread(task))

Is much easier to review, as it is obvious that it is checking if the task
is a user thread.

Using a coccinelle script, convert these checks over to using either
is_user_thread() or is_kernel_thread().

  $ 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

Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 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 +++---
 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 +-
 50 files changed, 72 insertions(+), 72 deletions(-)

diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
index 54bdca025c9f..48f8a9703910 100644
--- a/arch/arm/mm/init.c
+++ b/arch/arm/mm/init.c
@@ -390,7 +390,7 @@ static void update_sections_early(struct section_perm perms[], int n)
 	struct task_struct *t, *s;
 
 	for_each_process(t) {
-		if (t->flags & PF_KTHREAD)
+		if (is_kernel_thread(t))
 			continue;
 		for_each_thread(t, s)
 			if (s->mm)
diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index 5b91803201ef..d04e5e8e09b4 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -43,7 +43,7 @@ static inline int access_ok(const void __user *addr, unsigned long size)
 	 * the user address before checking.
 	 */
 	if (IS_ENABLED(CONFIG_ARM64_TAGGED_ADDR_ABI) &&
-	    (current->flags & PF_KTHREAD || test_thread_flag(TIF_TAGGED_ADDR)))
+	    (is_kernel_thread(current) || test_thread_flag(TIF_TAGGED_ADDR)))
 		addr = untagged_addr(addr);
 
 	return likely(__access_ok(addr, size));
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 42faebb7b712..0489bc69b434 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -514,7 +514,7 @@ static void ssbs_thread_switch(struct task_struct *next)
 	 * Nothing to do for kernel threads, but 'regs' may be junk
 	 * (e.g. idle task) so check the flags and bail early.
 	 */
-	if (unlikely(next->flags & PF_KTHREAD))
+	if (unlikely(is_kernel_thread(next)))
 		return;
 
 	/*
diff --git a/arch/arm64/kernel/proton-pack.c b/arch/arm64/kernel/proton-pack.c
index b198dde79e59..032e10445570 100644
--- a/arch/arm64/kernel/proton-pack.c
+++ b/arch/arm64/kernel/proton-pack.c
@@ -666,7 +666,7 @@ static void __update_pstate_ssbs(struct pt_regs *regs, bool state)
 void spectre_v4_enable_task_mitigation(struct task_struct *tsk)
 {
 	struct pt_regs *regs = task_pt_regs(tsk);
-	bool ssbs = false, kthread = tsk->flags & PF_KTHREAD;
+	bool ssbs = false, kthread = is_kernel_thread(tsk);
 
 	if (spectre_v4_mitigations_off())
 		ssbs = true;
diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c
index b630604c577f..6b4e9d371c4e 100644
--- a/arch/mips/kernel/process.c
+++ b/arch/mips/kernel/process.c
@@ -74,7 +74,7 @@ void exit_thread(struct task_struct *tsk)
 	 * User threads may have allocated a delay slot emulation frame.
 	 * If so, clean up that allocation.
 	 */
-	if (!(current->flags & PF_KTHREAD))
+	if (is_user_thread(current))
 		dsemul_thread_cleanup(tsk);
 }
 
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index ef91f71e07c4..d84466e5f376 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1770,7 +1770,7 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
 
 	klp_init_thread_info(p);
 
-	if (unlikely(p->flags & PF_KTHREAD)) {
+	if (unlikely(is_kernel_thread(p))) {
 		/* kernel thread */
 
 		/* Create initial minimum stack frame. */
diff --git a/arch/powerpc/kernel/stacktrace.c b/arch/powerpc/kernel/stacktrace.c
index 90882b5175cd..6290d095425d 100644
--- a/arch/powerpc/kernel/stacktrace.c
+++ b/arch/powerpc/kernel/stacktrace.c
@@ -76,7 +76,7 @@ int __no_sanitize_address arch_stack_walk_reliable(stack_trace_consume_fn consum
 	stack_end = stack_page + THREAD_SIZE;
 
 	// See copy_thread() for details.
-	if (task->flags & PF_KTHREAD)
+	if (is_kernel_thread(task))
 		stack_end -= STACK_FRAME_MIN_SIZE;
 	else
 		stack_end -= STACK_USER_INT_FRAME_SIZE;
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 91d6341f281f..90a32738842f 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -805,7 +805,7 @@ void fpregs_lock_and_load(void)
 	 * Warn about it.
 	 */
 	WARN_ON_ONCE(!irq_fpu_usable());
-	WARN_ON_ONCE(current->flags & PF_KTHREAD);
+	WARN_ON_ONCE(is_kernel_thread(current));
 
 	fpregs_lock();
 
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 962c3ce39323..e15fb4e260c5 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -220,7 +220,7 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
 	fpu_clone(p, clone_flags, args->fn, new_ssp);
 
 	/* Kernel thread ? */
-	if (unlikely(p->flags & PF_KTHREAD)) {
+	if (unlikely(is_kernel_thread(p))) {
 		p->thread.pkru = pkru_get_init_value();
 		memset(childregs, 0, sizeof(struct pt_regs));
 		kthread_frame_init(frame, args->fn, args->fn_arg);
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 5905f277057b..48e39fa3d3ad 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -2061,7 +2061,7 @@ void blkcg_maybe_throttle_current(void)
  */
 void blkcg_schedule_throttle(struct gendisk *disk, bool use_memdelay)
 {
-	if (unlikely(current->flags & PF_KTHREAD))
+	if (unlikely(is_kernel_thread(current)))
 		return;
 
 	if (current->throttle_disk != disk) {
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h
index b6ca41859b53..4df0691e5e1b 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h
@@ -279,7 +279,7 @@ bool amdgpu_amdkfd_compute_active(struct amdgpu_device *adev, uint32_t node_id);
 			pagefault_disable();				\
 			if ((mmptr) == current->mm) {			\
 				valid = !get_user((dst), (wptr));	\
-			} else if (current->flags & PF_KTHREAD) {	\
+			} else if (is_kernel_thread(current)) {	\
 				kthread_use_mm(mmptr);			\
 				valid = !get_user((dst), (wptr));	\
 				kthread_unuse_mm(mmptr);		\
diff --git a/drivers/md/dm-vdo/logger.c b/drivers/md/dm-vdo/logger.c
index 3f7dc2cb6b98..56f94f997487 100644
--- a/drivers/md/dm-vdo/logger.c
+++ b/drivers/md/dm-vdo/logger.c
@@ -137,7 +137,7 @@ static void emit_log_message(int priority, const char *module, const char *prefi
 	 * If it's a kernel thread and the module name is a prefix of its name, assume it is ours
 	 * and only identify the thread.
 	 */
-	if (((current->flags & PF_KTHREAD) != 0) &&
+	if ((is_kernel_thread(current)) &&
 	    (strncmp(module, current->comm, strlen(module)) == 0)) {
 		emit_log_message_to_kernel(priority, "%s: %s%pV%pV\n", current->comm,
 					   prefix, vaf1, vaf2);
diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index 6853c4660e7c..69ccce95052c 100644
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -360,7 +360,7 @@ static void send_sig_all(int sig)
 
 	read_lock(&tasklist_lock);
 	for_each_process(p) {
-		if (p->flags & PF_KTHREAD)
+		if (is_kernel_thread(p))
 			continue;
 		if (is_global_init(p))
 			continue;
diff --git a/fs/bcachefs/clock.c b/fs/bcachefs/clock.c
index d6dd12d74d4f..90a8f3134ea4 100644
--- a/fs/bcachefs/clock.c
+++ b/fs/bcachefs/clock.c
@@ -93,7 +93,7 @@ void bch2_io_clock_schedule_timeout(struct io_clock *clock, u64 until)
 void bch2_kthread_io_clock_wait(struct io_clock *clock,
 				u64 io_until, unsigned long cpu_timeout)
 {
-	bool kthread = (current->flags & PF_KTHREAD) != 0;
+	bool kthread = is_kernel_thread(current);
 	struct io_clock_wait wait = {
 		.io_timer.expire	= io_until,
 		.io_timer.fn		= io_clock_wait_fn,
diff --git a/fs/bcachefs/journal_reclaim.c b/fs/bcachefs/journal_reclaim.c
index 5d1547aa118a..bc7aec50c05b 100644
--- a/fs/bcachefs/journal_reclaim.c
+++ b/fs/bcachefs/journal_reclaim.c
@@ -665,7 +665,7 @@ static int __bch2_journal_reclaim(struct journal *j, bool direct, bool kicked)
 {
 	struct bch_fs *c = container_of(j, struct bch_fs, journal);
 	struct btree_cache *bc = &c->btree_cache;
-	bool kthread = (current->flags & PF_KTHREAD) != 0;
+	bool kthread = is_kernel_thread(current);
 	u64 seq_to_flush;
 	size_t min_nr, min_key_cache, nr_flushed;
 	unsigned flags;
diff --git a/fs/bcachefs/move.c b/fs/bcachefs/move.c
index fc396b9fa754..55e88842d5fc 100644
--- a/fs/bcachefs/move.c
+++ b/fs/bcachefs/move.c
@@ -487,7 +487,7 @@ int bch2_move_get_io_opts_one(struct btree_trans *trans,
 int bch2_move_ratelimit(struct moving_context *ctxt)
 {
 	struct bch_fs *c = ctxt->trans->c;
-	bool is_kthread = current->flags & PF_KTHREAD;
+	bool is_kthread = is_kernel_thread(current);
 	u64 delay;
 
 	if (ctxt->wait_on_copygc && c->copygc_running) {
@@ -749,7 +749,7 @@ static int __bch2_move_data_phys(struct moving_context *ctxt,
 {
 	struct btree_trans *trans = ctxt->trans;
 	struct bch_fs *c = trans->c;
-	bool is_kthread = current->flags & PF_KTHREAD;
+	bool is_kthread = is_kernel_thread(current);
 	struct bch_io_opts io_opts = bch2_opts_to_inode_opts(c->opts);
 	struct btree_iter iter = {}, bp_iter = {};
 	struct bkey_buf sk;
@@ -961,7 +961,7 @@ static int bch2_move_btree(struct bch_fs *c,
 			   move_btree_pred pred, void *arg,
 			   struct bch_move_stats *stats)
 {
-	bool kthread = (current->flags & PF_KTHREAD) != 0;
+	bool kthread = is_kernel_thread(current);
 	struct bch_io_opts io_opts = bch2_opts_to_inode_opts(c->opts);
 	struct moving_context ctxt;
 	struct btree_trans *trans;
diff --git a/fs/exec.c b/fs/exec.c
index 8e4ea5f1e64c..7c308786a1ed 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1983,7 +1983,7 @@ int kernel_execve(const char *kernel_filename,
 	int retval;
 
 	/* It is non-sense for kernel threads to call execve */
-	if (WARN_ON_ONCE(current->flags & PF_KTHREAD))
+	if (WARN_ON_ONCE(is_kernel_thread(current)))
 		return -EINVAL;
 
 	filename = getname_kernel(kernel_filename);
diff --git a/fs/file_table.c b/fs/file_table.c
index c04ed94cdc4b..e3332cc9091a 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -521,7 +521,7 @@ static void __fput_deferred(struct file *file)
 		return;
 	}
 
-	if (likely(!in_interrupt() && !(task->flags & PF_KTHREAD))) {
+	if (likely(!in_interrupt() && is_user_thread(task))) {
 		init_task_work(&file->f_task_work, ____fput);
 		if (!task_work_add(task, &file->f_task_work, TWA_RESUME))
 			return;
diff --git a/fs/namespace.c b/fs/namespace.c
index d9ca80dcc544..5e7ab6b9d9ef 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1509,7 +1509,7 @@ static void mntput_no_expire(struct mount *mnt)
 
 	if (likely(!(mnt->mnt.mnt_flags & MNT_INTERNAL))) {
 		struct task_struct *task = current;
-		if (likely(!(task->flags & PF_KTHREAD))) {
+		if (likely(is_user_thread(task))) {
 			init_task_work(&mnt->mnt_rcu, __cleanup_mnt);
 			if (!task_work_add(task, &mnt->mnt_rcu, TWA_RESUME))
 				return;
diff --git a/fs/proc/array.c b/fs/proc/array.c
index d6a0369caa93..478f8f380240 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -106,7 +106,7 @@ void proc_task_name(struct seq_file *m, struct task_struct *p, bool escape)
 	 */
 	if (p->flags & PF_WQ_WORKER)
 		wq_worker_comm(tcomm, sizeof(tcomm), p);
-	else if (p->flags & PF_KTHREAD)
+	else if (is_kernel_thread(p))
 		get_kthread_comm(tcomm, sizeof(tcomm), p);
 	else
 		get_task_comm(tcomm, p);
@@ -221,7 +221,7 @@ static inline void task_state(struct seq_file *m, struct pid_namespace *ns,
 #endif
 	seq_putc(m, '\n');
 
-	seq_printf(m, "Kthread:\t%c\n", p->flags & PF_KTHREAD ? '1' : '0');
+	seq_printf(m, "Kthread:\t%c\n", is_kernel_thread(p) ? '1' : '0');
 }
 
 void render_sigset_t(struct seq_file *m, const char *header,
diff --git a/fs/proc/base.c b/fs/proc/base.c
index b0d4e1908b22..43270431edfe 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1179,7 +1179,7 @@ static int __set_oom_adj(struct file *file, int oom_adj, bool legacy)
 				continue;
 
 			/* do not touch kernel threads or the global init */
-			if (p->flags & PF_KTHREAD || is_global_init(p))
+			if (is_kernel_thread(p) || is_global_init(p))
 				continue;
 
 			task_lock(p);
@@ -1330,7 +1330,7 @@ static ssize_t proc_loginuid_write(struct file * file, const char __user * buf,
 	int rv;
 
 	/* Don't let kthreads write their own loginuid */
-	if (current->flags & PF_KTHREAD)
+	if (is_kernel_thread(current))
 		return -EPERM;
 
 	rcu_read_lock();
@@ -1876,7 +1876,7 @@ void task_dump_owner(struct task_struct *task, umode_t mode,
 	kuid_t uid;
 	kgid_t gid;
 
-	if (unlikely(task->flags & PF_KTHREAD)) {
+	if (unlikely(is_kernel_thread(task))) {
 		*ruid = GLOBAL_ROOT_UID;
 		*rgid = GLOBAL_ROOT_GID;
 		return;
diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index c6209fe44cb1..27de67fc2642 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -523,7 +523,7 @@ static void io_queue_iowq(struct io_kiocb *req)
 
 	BUG_ON(!tctx);
 
-	if ((current->flags & PF_KTHREAD) || !tctx->io_wq) {
+	if (is_kernel_thread(current) || !tctx->io_wq) {
 		io_req_task_queue_fail(req, -ECANCELED);
 		return;
 	}
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 3caf2cd86e65..32489f321605 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -4033,7 +4033,7 @@ static void __cgroup_kill(struct cgroup *cgrp)
 	css_task_iter_start(&cgrp->self, CSS_TASK_ITER_PROCS | CSS_TASK_ITER_THREADED, &it);
 	while ((task = css_task_iter_next(&it))) {
 		/* Ignore kernel threads here. */
-		if (task->flags & PF_KTHREAD)
+		if (is_kernel_thread(task))
 			continue;
 
 		/* Skip tasks that are already dying. */
@@ -6718,7 +6718,7 @@ void cgroup_post_fork(struct task_struct *child,
 		cset = NULL;
 	}
 
-	if (!(child->flags & PF_KTHREAD)) {
+	if (is_user_thread(child)) {
 		if (unlikely(test_bit(CGRP_FREEZE, &cgrp_flags))) {
 			/*
 			 * If the cgroup has to be frozen, the new task has
@@ -6800,7 +6800,7 @@ void cgroup_exit(struct task_struct *tsk)
 		dec_dl_tasks_cs(tsk);
 
 	WARN_ON_ONCE(cgroup_task_frozen(tsk));
-	if (unlikely(!(tsk->flags & PF_KTHREAD) &&
+	if (unlikely(is_user_thread(tsk) &&
 		     test_bit(CGRP_FREEZE, &task_dfl_cgroup(tsk)->flags)))
 		cgroup_update_frozen(task_dfl_cgroup(tsk));
 
diff --git a/kernel/cgroup/freezer.c b/kernel/cgroup/freezer.c
index bf1690a167dd..cc216173b355 100644
--- a/kernel/cgroup/freezer.c
+++ b/kernel/cgroup/freezer.c
@@ -196,7 +196,7 @@ static void cgroup_do_freeze(struct cgroup *cgrp, bool freeze)
 		 * Ignore kernel threads here. Freezing cgroups containing
 		 * kthreads isn't supported.
 		 */
-		if (task->flags & PF_KTHREAD)
+		if (is_kernel_thread(task))
 			continue;
 		cgroup_freeze_task(task, freeze);
 	}
@@ -224,7 +224,7 @@ void cgroup_freezer_migrate_task(struct task_struct *task,
 	/*
 	 * Kernel threads are not supposed to be frozen at all.
 	 */
-	if (task->flags & PF_KTHREAD)
+	if (is_kernel_thread(task))
 		return;
 
 	/*
diff --git a/kernel/events/core.c b/kernel/events/core.c
index e93c19565914..9c482e6f51ba 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7317,7 +7317,7 @@ static void perf_sample_regs_user(struct perf_regs *regs_user,
 	if (user_mode(regs)) {
 		regs_user->abi = perf_reg_abi(current);
 		regs_user->regs = regs;
-	} else if (!(current->flags & PF_KTHREAD)) {
+	} else if (is_user_thread(current)) {
 		perf_get_regs_user(regs_user, regs);
 	} else {
 		regs_user->abi = PERF_SAMPLE_REGS_ABI_NONE;
diff --git a/kernel/exit.c b/kernel/exit.c
index 1b51dc099f1e..5c10f9ea39d7 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -533,7 +533,7 @@ void mm_update_next_owner(struct mm_struct *mm)
 	for_each_process(g) {
 		if (atomic_read(&mm->mm_users) <= 1)
 			break;
-		if (g->flags & PF_KTHREAD)
+		if (is_kernel_thread(g))
 			continue;
 		if (try_to_set_owner(g, mm))
 			goto ret;
diff --git a/kernel/fork.c b/kernel/fork.c
index c4b26cd8998b..e3a844a7d55b 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -586,7 +586,7 @@ void free_task(struct task_struct *tsk)
 	rt_mutex_debug_task_free(tsk);
 	ftrace_graph_exit_task(tsk);
 	arch_release_task_struct(tsk);
-	if (tsk->flags & PF_KTHREAD)
+	if (is_kernel_thread(tsk))
 		free_kthread_struct(tsk);
 	bpf_task_storage_free(tsk);
 	free_task_struct(tsk);
@@ -1545,7 +1545,7 @@ struct file *get_task_exe_file(struct task_struct *task)
 	struct file *exe_file = NULL;
 	struct mm_struct *mm;
 
-	if (task->flags & PF_KTHREAD)
+	if (is_kernel_thread(task))
 		return NULL;
 
 	task_lock(task);
@@ -1570,7 +1570,7 @@ struct mm_struct *get_task_mm(struct task_struct *task)
 {
 	struct mm_struct *mm;
 
-	if (task->flags & PF_KTHREAD)
+	if (is_kernel_thread(task))
 		return NULL;
 
 	task_lock(task);
diff --git a/kernel/freezer.c b/kernel/freezer.c
index 8d530d0949ff..136008461ee0 100644
--- a/kernel/freezer.c
+++ b/kernel/freezer.c
@@ -46,7 +46,7 @@ bool freezing_slow_path(struct task_struct *p)
 	if (pm_nosig_freezing || cgroup_freezing(p))
 		return true;
 
-	if (pm_freezing && !(p->flags & PF_KTHREAD))
+	if (pm_freezing && is_user_thread(p))
 		return true;
 
 	return false;
@@ -170,7 +170,7 @@ bool freeze_task(struct task_struct *p)
 		return false;
 	}
 
-	if (!(p->flags & PF_KTHREAD))
+	if (is_user_thread(p))
 		fake_signal_wake_up(p);
 	else
 		wake_up_state(p, TASK_NORMAL);
diff --git a/kernel/futex/pi.c b/kernel/futex/pi.c
index 7a941845f7ee..dcbe6c6927d0 100644
--- a/kernel/futex/pi.c
+++ b/kernel/futex/pi.c
@@ -428,7 +428,7 @@ static int attach_to_pi_owner(u32 __user *uaddr, u32 uval, union futex_key *key,
 	if (!p)
 		return handle_exit_race(uaddr, uval, NULL);
 
-	if (unlikely(p->flags & PF_KTHREAD)) {
+	if (unlikely(is_kernel_thread(p))) {
 		put_task_struct(p);
 		return -EPERM;
 	}
diff --git a/kernel/kthread.c b/kernel/kthread.c
index 77c44924cf54..1f2b28076345 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -81,7 +81,7 @@ enum KTHREAD_BITS {
 
 static inline struct kthread *to_kthread(struct task_struct *k)
 {
-	WARN_ON(!(k->flags & PF_KTHREAD));
+	WARN_ON(is_user_thread(k));
 	return k->worker_private;
 }
 
@@ -99,7 +99,7 @@ static inline struct kthread *to_kthread(struct task_struct *k)
 static inline struct kthread *__to_kthread(struct task_struct *p)
 {
 	void *kthread = p->worker_private;
-	if (kthread && !(p->flags & PF_KTHREAD))
+	if (kthread && is_user_thread(p))
 		kthread = NULL;
 	return kthread;
 }
@@ -1601,7 +1601,7 @@ void kthread_use_mm(struct mm_struct *mm)
 	struct mm_struct *active_mm;
 	struct task_struct *tsk = current;
 
-	WARN_ON_ONCE(!(tsk->flags & PF_KTHREAD));
+	WARN_ON_ONCE(is_user_thread(tsk));
 	WARN_ON_ONCE(tsk->mm);
 
 	/*
@@ -1646,7 +1646,7 @@ void kthread_unuse_mm(struct mm_struct *mm)
 {
 	struct task_struct *tsk = current;
 
-	WARN_ON_ONCE(!(tsk->flags & PF_KTHREAD));
+	WARN_ON_ONCE(is_user_thread(tsk));
 	WARN_ON_ONCE(!tsk->mm);
 
 	task_lock(tsk);
@@ -1686,7 +1686,7 @@ void kthread_associate_blkcg(struct cgroup_subsys_state *css)
 {
 	struct kthread *kthread;
 
-	if (!(current->flags & PF_KTHREAD))
+	if (is_user_thread(current))
 		return;
 	kthread = to_kthread(current);
 	if (!kthread)
@@ -1712,7 +1712,7 @@ struct cgroup_subsys_state *kthread_blkcg(void)
 {
 	struct kthread *kthread;
 
-	if (current->flags & PF_KTHREAD) {
+	if (is_kernel_thread(current)) {
 		kthread = to_kthread(current);
 		if (kthread)
 			return kthread->blkcg_css;
diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
index ba069459c101..f5bf80b9d768 100644
--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c
@@ -423,7 +423,7 @@ static void klp_send_signals(void)
 		 * Meanwhile the task could migrate itself and the action
 		 * would be meaningless. It is not serious though.
 		 */
-		if (task->flags & PF_KTHREAD) {
+		if (is_kernel_thread(task)) {
 			/*
 			 * Wake up a kthread which sleeps interruptedly and
 			 * still has not been migrated.
diff --git a/kernel/power/process.c b/kernel/power/process.c
index 66ac067d9ae6..b3fe1067bfed 100644
--- a/kernel/power/process.c
+++ b/kernel/power/process.c
@@ -223,7 +223,7 @@ void thaw_kernel_threads(void)
 
 	read_lock(&tasklist_lock);
 	for_each_process_thread(g, p) {
-		if (p->flags & PF_KTHREAD)
+		if (is_kernel_thread(p))
 			__thaw_task(p);
 	}
 	read_unlock(&tasklist_lock);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index c81cf642dba0..baea079e930f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2448,7 +2448,7 @@ static inline bool is_cpu_allowed(struct task_struct *p, int cpu)
 		return cpu_online(cpu);
 
 	/* Non kernel threads are not allowed during either online or offline. */
-	if (!(p->flags & PF_KTHREAD))
+	if (is_user_thread(p))
 		return cpu_active(cpu);
 
 	/* KTHREAD_IS_PER_CPU is always allowed. */
@@ -3074,7 +3074,7 @@ static int __set_cpus_allowed_ptr_locked(struct task_struct *p,
 {
 	const struct cpumask *cpu_allowed_mask = task_cpu_possible_mask(p);
 	const struct cpumask *cpu_valid_mask = cpu_active_mask;
-	bool kthread = p->flags & PF_KTHREAD;
+	bool kthread = is_kernel_thread(p);
 	unsigned int dest_cpu;
 	int ret = 0;
 
@@ -8895,7 +8895,7 @@ void normalize_rt_tasks(void)
 		/*
 		 * Only normalize user tasks:
 		 */
-		if (p->flags & PF_KTHREAD)
+		if (is_kernel_thread(p))
 			continue;
 
 		p->se.exec_start = 0;
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 2c85c86b455f..adb6afc1a7c5 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -387,7 +387,7 @@ void play_idle_precise(u64 duration_ns, u64 latency_ns)
 	 */
 	WARN_ON_ONCE(current->policy != SCHED_FIFO);
 	WARN_ON_ONCE(current->nr_cpus_allowed != 1);
-	WARN_ON_ONCE(!(current->flags & PF_KTHREAD));
+	WARN_ON_ONCE(is_user_thread(current));
 	WARN_ON_ONCE(!(current->flags & PF_NO_SETAFFINITY));
 	WARN_ON_ONCE(!duration_ns);
 	WARN_ON_ONCE(current->mm);
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 47972f34ea70..cb835fc6854c 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2571,7 +2571,7 @@ static inline bool task_allowed_on_cpu(struct task_struct *p, int cpu)
 		return false;
 
 	/* Can @cpu run a user thread? */
-	if (!(p->flags & PF_KTHREAD) && !task_cpu_possible(cpu, p))
+	if (is_user_thread(p) && !task_cpu_possible(cpu, p))
 		return false;
 
 	return true;
@@ -3556,7 +3556,7 @@ static inline void membarrier_switch_mm(struct rq *rq,
 #ifdef CONFIG_SMP
 static inline bool is_per_cpu_kthread(struct task_struct *p)
 {
-	if (!(p->flags & PF_KTHREAD))
+	if (is_user_thread(p))
 		return false;
 
 	if (p->nr_cpus_allowed != 1)
diff --git a/kernel/signal.c b/kernel/signal.c
index f8859faa26c5..0157f2c55158 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -96,7 +96,7 @@ static bool sig_task_ignored(struct task_struct *t, int sig, bool force)
 		return true;
 
 	/* Only allow kernel generated signals to this kthread */
-	if (unlikely((t->flags & PF_KTHREAD) &&
+	if (unlikely(is_kernel_thread(t) &&
 		     (handler == SIG_KTHREAD_KERNEL) && !force))
 		return true;
 
@@ -1067,7 +1067,7 @@ static int __send_signal_locked(int sig, struct kernel_siginfo *info,
 	/*
 	 * Skip useless siginfo allocation for SIGKILL and kernel threads.
 	 */
-	if ((sig == SIGKILL) || (t->flags & PF_KTHREAD))
+	if ((sig == SIGKILL) || is_kernel_thread(t))
 		goto out_set;
 
 	/*
diff --git a/kernel/stacktrace.c b/kernel/stacktrace.c
index afb3c116da91..f1e886c77f95 100644
--- a/kernel/stacktrace.c
+++ b/kernel/stacktrace.c
@@ -229,7 +229,7 @@ unsigned int stack_trace_save_user(unsigned long *store, unsigned int size)
 	};
 
 	/* Trace user stack if not a kernel thread */
-	if (current->flags & PF_KTHREAD)
+	if (is_kernel_thread(current))
 		return 0;
 
 	arch_stack_walk_user(consume_entry, &c, task_pt_regs(current));
diff --git a/lib/is_single_threaded.c b/lib/is_single_threaded.c
index 8c98b20bfc41..45321514da12 100644
--- a/lib/is_single_threaded.c
+++ b/lib/is_single_threaded.c
@@ -28,7 +28,7 @@ bool current_is_single_threaded(void)
 	ret = false;
 	rcu_read_lock();
 	for_each_process(p) {
-		if (unlikely(p->flags & PF_KTHREAD))
+		if (unlikely(is_kernel_thread(p)))
 			continue;
 		if (unlikely(p == task->group_leader))
 			continue;
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c96c1f2b9cf5..2195ee072e7f 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2555,7 +2555,7 @@ static struct obj_cgroup *current_objcg_update(void)
 		}
 
 		/* If new objcg is NULL, no reason for the second atomic update. */
-		if (!current->mm || (current->flags & PF_KTHREAD))
+		if (!current->mm || is_kernel_thread(current))
 			return NULL;
 
 		/*
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 25923cfec9c6..681cf8ac0f1a 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -164,7 +164,7 @@ static bool oom_unkillable_task(struct task_struct *p)
 {
 	if (is_global_init(p))
 		return true;
-	if (p->flags & PF_KTHREAD)
+	if (is_kernel_thread(p))
 		return true;
 	return false;
 }
@@ -987,7 +987,7 @@ static void __oom_kill_process(struct task_struct *victim, const char *message)
 		 * No kthread_use_mm() user needs to read from the userspace so
 		 * we are ok to reap it.
 		 */
-		if (unlikely(p->flags & PF_KTHREAD))
+		if (unlikely(is_kernel_thread(p)))
 			continue;
 		do_send_sig_info(SIGKILL, SEND_SIG_PRIV, p, PIDTYPE_TGID);
 	}
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 5669baf2a6fe..2486e2d33cc4 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -590,7 +590,7 @@ static inline struct capture_control *task_capc(struct zone *zone)
 	struct capture_control *capc = current->capture_control;
 
 	return unlikely(capc) &&
-		!(current->flags & PF_KTHREAD) &&
+		is_user_thread(current) &&
 		!capc->page &&
 		capc->cc->zone == zone ? capc : NULL;
 }
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 3783e45bfc92..3169463c5eb6 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -6478,7 +6478,7 @@ static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
 	 * committing a transaction where throttling it could forcing other
 	 * processes to block on log_wait_commit().
 	 */
-	if (current->flags & PF_KTHREAD)
+	if (is_kernel_thread(current))
 		goto out;
 
 	/*
diff --git a/security/keys/request_key.c b/security/keys/request_key.c
index a7673ad86d18..befed0968068 100644
--- a/security/keys/request_key.c
+++ b/security/keys/request_key.c
@@ -39,7 +39,7 @@ static void cache_requested_key(struct key *key)
 	struct task_struct *t = current;
 
 	/* Do not cache key if it is a kernel thread */
-	if (!(t->flags & PF_KTHREAD)) {
+	if (is_user_thread(t)) {
 		key_put(t->cached_requested_key);
 		t->cached_requested_key = key_get(key);
 		set_tsk_thread_flag(t, TIF_NOTIFY_RESUME);
diff --git a/security/smack/smack_access.c b/security/smack/smack_access.c
index 2e4a0cb22782..971f8cc7ad9c 100644
--- a/security/smack/smack_access.c
+++ b/security/smack/smack_access.c
@@ -697,7 +697,7 @@ bool smack_privileged(int cap)
 	/*
 	 * All kernel tasks are privileged
 	 */
-	if (unlikely(current->flags & PF_KTHREAD))
+	if (unlikely(is_kernel_thread(current)))
 		return true;
 
 	return smack_privileged_cred(cap, current_cred());
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 99833168604e..53b10b9ba5d0 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -2408,7 +2408,7 @@ static int smack_sk_alloc_security(struct sock *sk, int family, gfp_t gfp_flags)
 	/*
 	 * Sockets created by kernel threads receive web label.
 	 */
-	if (unlikely(current->flags & PF_KTHREAD)) {
+	if (unlikely(is_kernel_thread(current))) {
 		ssp->smk_in = &smack_known_web;
 		ssp->smk_out = &smack_known_web;
 	} else {
@@ -2950,7 +2950,7 @@ static int smack_socket_post_create(struct socket *sock, int family,
 	/*
 	 * Sockets created by kernel threads receive web label.
 	 */
-	if (unlikely(current->flags & PF_KTHREAD)) {
+	if (unlikely(is_kernel_thread(current))) {
 		ssp = smack_sock(sock->sk);
 		ssp->smk_in = &smack_known_web;
 		ssp->smk_out = &smack_known_web;
diff --git a/security/tomoyo/network.c b/security/tomoyo/network.c
index 8dc61335f65e..9e63cf45c200 100644
--- a/security/tomoyo/network.c
+++ b/security/tomoyo/network.c
@@ -613,7 +613,7 @@ static int tomoyo_check_unix_address(struct sockaddr *addr,
 static bool tomoyo_kernel_service(void)
 {
 	/* Nothing to do if I am a kernel service. */
-	return current->flags & PF_KTHREAD;
+	return is_kernel_thread(current);
 }
 
 /**
diff --git a/security/yama/yama_lsm.c b/security/yama/yama_lsm.c
index 3d064dd4e03f..c3b72dd8e86c 100644
--- a/security/yama/yama_lsm.c
+++ b/security/yama/yama_lsm.c
@@ -79,7 +79,7 @@ static void report_access(const char *access, struct task_struct *target,
 
 	assert_spin_locked(&target->alloc_lock); /* for target->comm */
 
-	if (current->flags & PF_KTHREAD) {
+	if (is_kernel_thread(current)) {
 		/* I don't think kthreads call task_work_run() before exiting.
 		 * Imagine angry ranting about procfs here.
 		 */
diff --git a/tools/sched_ext/scx_central.bpf.c b/tools/sched_ext/scx_central.bpf.c
index 50bc1737c167..f054a14b9156 100644
--- a/tools/sched_ext/scx_central.bpf.c
+++ b/tools/sched_ext/scx_central.bpf.c
@@ -111,7 +111,7 @@ void BPF_STRUCT_OPS(central_enqueue, struct task_struct *p, u64 enq_flags)
 	 * behind other threads which is necessary for forward progress
 	 * guarantee as we depend on the BPF timer which may run from ksoftirqd.
 	 */
-	if ((p->flags & PF_KTHREAD) && p->nr_cpus_allowed == 1) {
+	if (is_kernel_thread(p) && p->nr_cpus_allowed == 1) {
 		__sync_fetch_and_add(&nr_locals, 1);
 		scx_bpf_dsq_insert(p, SCX_DSQ_LOCAL, SCX_SLICE_INF,
 				   enq_flags | SCX_ENQ_PREEMPT);
diff --git a/tools/sched_ext/scx_flatcg.bpf.c b/tools/sched_ext/scx_flatcg.bpf.c
index 2c720e3ecad5..07f4d3a6833c 100644
--- a/tools/sched_ext/scx_flatcg.bpf.c
+++ b/tools/sched_ext/scx_flatcg.bpf.c
@@ -370,7 +370,7 @@ void BPF_STRUCT_OPS(fcg_enqueue, struct task_struct *p, u64 enq_flags)
 		 * implement per-cgroup fallback dq's instead so that we have
 		 * more control over when tasks with custom cpumask get issued.
 		 */
-		if (p->nr_cpus_allowed == 1 && (p->flags & PF_KTHREAD)) {
+		if (p->nr_cpus_allowed == 1 && is_kernel_thread(p)) {
 			stat_inc(FCG_STAT_LOCAL);
 			scx_bpf_dsq_insert(p, SCX_DSQ_LOCAL, SCX_SLICE_DFL,
 					   enq_flags);
diff --git a/tools/sched_ext/scx_qmap.bpf.c b/tools/sched_ext/scx_qmap.bpf.c
index 26c40ca4f36c..b8ea1bb436b2 100644
--- a/tools/sched_ext/scx_qmap.bpf.c
+++ b/tools/sched_ext/scx_qmap.bpf.c
@@ -200,7 +200,7 @@ void BPF_STRUCT_OPS(qmap_enqueue, struct task_struct *p, u64 enq_flags)
 	void *ring;
 	s32 cpu;
 
-	if (p->flags & PF_KTHREAD) {
+	if (is_kernel_thread(p)) {
 		if (stall_kernel_nth && !(++kernel_cnt % stall_kernel_nth))
 			return;
 	} else {
-- 
2.47.2

Re: [RFC][PATCH 2/2] treewide: Have the task->flags & PF_KTHREAD check use the helper functions

[Kees Cook]

On Fri, Apr 25, 2025 at 04:41:22PM -0400, Steven Rostedt wrote:
> From: Steven Rostedt <rostedt@goodmis.org>
> 
> Getting the check if a task is a kernel thread or a user thread can be
> error prone as it's not easy to see the difference.
> 
> 	if (!(task->flags & PF_KTHREAD))
> 
> Is not immediately obvious that it's checking for a user thread.
> 
> 	if (is_user_thread(task))
> 
> Is much easier to review, as it is obvious that it is checking if the task
> is a user thread.
> 
> Using a coccinelle script, convert these checks over to using either
> is_user_thread() or is_kernel_thread().
> 
>   $ 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

FYI, the "file in" test can be helpful. I use it to exclude tools and
samples regularly, and *I think* it would work for excluding individual
files too:

@name_of_rule depends !(file in "tools") && !(file in "samples")@

I've been collecting random notes like this here:

https://github.com/kees/kernel-tools/tree/trunk/coccinelle

>  tools/sched_ext/scx_central.bpf.c          |  2 +-
>  tools/sched_ext/scx_flatcg.bpf.c           |  2 +-
>  tools/sched_ext/scx_qmap.bpf.c             |  2 +-

I think these are fine. The Makefile is pulling in standard kbuild
Makefiles, so I think the correct include directories (outside of
tools/) are being used.

But yeah, easy mechanical change and a readability improvement. :)

Reviewed-by: Kees Cook <kees@kernel.org>

-- 
Kees Cook

Re: [RFC][PATCH 2/2] treewide: Have the task->flags & PF_KTHREAD check use the helper functions

[Alexei Starovoitov]

On Fri, Apr 25, 2025 at 4:10 PM Kees Cook <kees@kernel.org> wrote:
>
> On Fri, Apr 25, 2025 at 04:41:22PM -0400, Steven Rostedt wrote:
> > From: Steven Rostedt <rostedt@goodmis.org>
> >
> > Getting the check if a task is a kernel thread or a user thread can be
> > error prone as it's not easy to see the difference.
> >
> >       if (!(task->flags & PF_KTHREAD))
> >
> > Is not immediately obvious that it's checking for a user thread.
> >
> >       if (is_user_thread(task))
> >
> > Is much easier to review, as it is obvious that it is checking if the task
> > is a user thread.
> >
> > Using a coccinelle script, convert these checks over to using either
> > is_user_thread() or is_kernel_thread().
> >
> >   $ 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
>
> FYI, the "file in" test can be helpful. I use it to exclude tools and
> samples regularly, and *I think* it would work for excluding individual
> files too:
>
> @name_of_rule depends !(file in "tools") && !(file in "samples")@
>
> I've been collecting random notes like this here:
>
> https://github.com/kees/kernel-tools/tree/trunk/coccinelle
>
> >  tools/sched_ext/scx_central.bpf.c          |  2 +-
> >  tools/sched_ext/scx_flatcg.bpf.c           |  2 +-
> >  tools/sched_ext/scx_qmap.bpf.c             |  2 +-
>
> I think these are fine. The Makefile is pulling in standard kbuild
> Makefiles, so I think the correct include directories (outside of
> tools/) are being used.

I suspect they are not fine.
I don't think they #include linux/sched.h
I would drop them for now.

Tejun,
please double check.

Re: [RFC][PATCH 2/2] treewide: Have the task->flags & PF_KTHREAD check use the helper functions

[Tejun Heo]

On Fri, Apr 25, 2025 at 08:22:59PM -0700, Alexei Starovoitov wrote:
> > >  tools/sched_ext/scx_central.bpf.c          |  2 +-
> > >  tools/sched_ext/scx_flatcg.bpf.c           |  2 +-
> > >  tools/sched_ext/scx_qmap.bpf.c             |  2 +-
> >
> > I think these are fine. The Makefile is pulling in standard kbuild
> > Makefiles, so I think the correct include directories (outside of
> > tools/) are being used.
> 
> I suspect they are not fine.
> I don't think they #include linux/sched.h
> I would drop them for now.

Oh, this won't work. Those get all the kernel defs from the BTF generated
vmlinux.h file which doesn't include any inline functions or macros, so
please don't include them in this conversion.

Thanks.

-- 
tejun

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

[Andrew Morton]

On Fri, 25 Apr 2025 16:41:20 -0400 Steven Rostedt <rostedt@goodmis.org> wrote:

> 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.

Seems sensible.  Please consider renaming PF_KTHREAD in order to break
missed conversion sites.

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

[Julia Lawall]

On Fri, 25 Apr 2025, Andrew Morton wrote:

> On Fri, 25 Apr 2025 16:41:20 -0400 Steven Rostedt <rostedt@goodmis.org> wrote:
>
> > 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.
>
> Seems sensible.  Please consider renaming PF_KTHREAD in order to break
> missed conversion sites.

Maybe:

@r depends on !(file in "include/linux/sched.h")@ // Kees's suggestion
position p;
expression e;
@@

(
e = (PF_KTHREAD | ...)
|
e |= (PF_KTHREAD | ...)
|
PF_KTHREAD@p
)

@script:ocaml@ // change to python if desired
p << r.p;
@@

Printf.printf "%s:%d: Warning: remaining use of PF_KTHREAD\n" (List.hd p).file (List.hd p).line

julia

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

[Steven Rostedt]

On Fri, 25 Apr 2025 16:14:49 -0700
Andrew Morton <akpm@linux-foundation.org> wrote:

> Seems sensible.  Please consider renaming PF_KTHREAD in order to break
> missed conversion sites.

It's not wrong to use the thread. I just find using these helper
functions a bit easier to review code. There's also some places that
have special tests where it can't use the flag:

kernel/sched/core.c:    if (!curr->mm || (curr->flags & (PF_EXITING | PF_KTHREAD)) ||
kernel/sched/fair.c:    if (!curr->mm || (curr->flags & (PF_EXITING | PF_KTHREAD)) || work->next != work)
kernel/trace/bpf_trace.c:                    current->flags & (PF_KTHREAD | PF_EXITING)))
kernel/trace/bpf_trace.c:       if (unlikely(task->flags & (PF_KTHREAD | PF_EXITING)))

Maybe we can have a: is_user_exiting_or_kthread() ?

Note, for coccinelle patches, I would wait till the end of the merge
window, run the scripts on what's in Linus's tree, run my tests, and
then submit. This way it catches most of the conversions with the least
amount of conflicts.

-- Steve

[PATCH] sched/core: Introduce task_*() helpers for PF_ flags

[Ingo Molnar]

* Steven Rostedt <rostedt@goodmis.org> wrote:

> On Fri, 25 Apr 2025 16:14:49 -0700
> Andrew Morton <akpm@linux-foundation.org> wrote:
> 
> > Seems sensible.  Please consider renaming PF_KTHREAD in order to break
> > missed conversion sites.
> 
> It's not wrong to use the thread. I just find using these helper
> functions a bit easier to review code. There's also some places that
> have special tests where it can't use the flag:
> 
> kernel/sched/core.c:    if (!curr->mm || (curr->flags & (PF_EXITING | PF_KTHREAD)) ||
> kernel/sched/fair.c:    if (!curr->mm || (curr->flags & (PF_EXITING | PF_KTHREAD)) || work->next != work)
> kernel/trace/bpf_trace.c:                    current->flags & (PF_KTHREAD | PF_EXITING)))
> kernel/trace/bpf_trace.c:       if (unlikely(task->flags & (PF_KTHREAD | PF_EXITING)))
> 
> Maybe we can have a: is_user_exiting_or_kthread() ?

No, we don't need is_user_exiting_or_kthread(). At all. Ever. In this 
universe. Or in any alternative universes. We don't even need 
is_user_exiting_or_kthread() in horror fiction novels written for 
kernel developers: there's really a limit to the level of horror that 
people are able to accept. Sheesh ...

This:

	if (task_kthread(task) || task_exiting(task))
		...

is a perfectly fine and readable C expression.

There's also *zero* reason for the whole is_*() complication your 
methods introduce. There's no need for 'is_' if we put a proper noun as 
a prefix before these methods, such as task_*(), and it also nicely 
organizes the namespace!

Let's not complicate trivial use of C logical operators unnecessarily, 
and let's not suck at namespaces more than we need to, 'kay?

( What's next, are we going to redefine 'if (x)' statements???
  ... wait a minute ... ;-)

The attached patch does the sane thing and introduces the following 
helpers for PF_ flags:

	/*
	 * Helpers for PF_ flags:
	 */
	#define task_vcpu(task)				((task)->flags & PF_VCPU)
	#define task_idle(task)				((task)->flags & PF_IDLE)
	#define task_exiting(task)			((task)->flags & PF_EXITING)
	#define task_postcoredump(task)			((task)->flags & PF_POSTCOREDUMP)
	#define task_io_worker(task)			((task)->flags & PF_IO_WORKER)
	#define task_wq_worker(task)			((task)->flags & PF_WQ_WORKER)
	#define task_forknoexec(task)			((task)->flags & PF_FORKNOEXEC)
	#define task_mce_process(task)			((task)->flags & PF_MCE_PROCESS)
	#define task_superpriv(task)			((task)->flags & PF_SUPERPRIV)
	#define task_dumpcore(task)			((task)->flags & PF_DUMPCORE)
	#define task_signaled(task)			((task)->flags & PF_SIGNALED)
	#define task_memalloc(task)			((task)->flags & PF_MEMALLOC)
	#define task_nproc_exceeded(task)		((task)->flags & PF_NPROC_EXCEEDED)
	#define task_used_math(task)			((task)->flags & PF_USED_MATH)
	#define task_user_worker(task)			((task)->flags & PF_USER_WORKER)
	#define task_nofreeze(task)			((task)->flags & PF_NOFREEZE)
	#define task_kcompactd(task)			((task)->flags & PF_KCOMPACTD)
	#define task_kswapd(task)			((task)->flags & PF_KSWAPD)
	#define task_memalloc_nofs(task)		((task)->flags & PF_MEMALLOC_NOFS)
	#define task_memalloc_noio(task)		((task)->flags & PF_MEMALLOC_NOIO)
	#define task_local_throttle(task)		((task)->flags & PF_LOCAL_THROTTLE)
	#define task_kthread(task)			((task)->flags & PF_KTHREAD)
	#define task_randomize(task)			((task)->flags & PF_RANDOMIZE)
	#define task_no_setaffinity(task)		((task)->flags & PF_NO_SETAFFINITY)
	#define task_mce_early(task)			((task)->flags & PF_MCE_EARLY)
	#define task_memalloc_pin(task)			((task)->flags & PF_MEMALLOC_PIN)
	#define task_block_ts(task)			((task)->flags & PF_BLOCK_TS)
	#define task_suspend_task(task)			((task)->flags & PF_SUSPEND_TASK)

These are easy names, precise lower-case variants of the PF_ flag 
names: if you know the PF flag's name, you know the helper's name as 
well.

And no, we don't need separate helpers for !task_kthread() et al: the C 
logical negation unary operator is perfectly readable when placed 
before a function call or a macro invocation, and a competent Linux 
kernel developer is expected to recognize it on sight:

	if (!task_kthread(task))
		...

Let's not infantilize the kernel source...

You can find this patch in my tree at:

	git://git.kernel.org/pub/scm/linux/kernel/git/mingo/tip.git WIP.sched/core

Note that I plan to add a few more patches as well, while we are 
touching this area:

 - tsk_used_math() is now overlapping and should be consolidated a bit. 
   And the used_math() indirection should go away as well.

 - I'll add conversion patches as well, at minimum for the top 10 flags 
   that cover 90%+ of the PF_ flag usage:

             nr of uses | flag
             -------------------------
		      7 | PF_USED_MATH
		      8 | PF_USER_WORKER
		     10   PF_NOFREEZE
		     15   PF_WQ_WORKER
		     18   PF_NO_SETAFFINITY
		     18   PF_VCPU
		     24   PF_RANDOMIZE
		     30   PF_MEMALLOC
		     73   PF_EXITING
		     92   PF_KTHREAD

   [ Or maybe for all of them - see below wrt. set_task_*(). ]

 - PF_ goes for 'per-process flag' and as such it is a total misnomer, 
   proudly misrepresented in <linux/sched.h>:

	/*
	 * Per process flags
	 */
	#define PF_VCPU                 0x00000001      /* I'm a virtual CPU */
	#define PF_IDLE                 0x00000002      /* I am an IDLE thread */

   Yeah, no: the PF_ flags haven't been "per process" ever since we 
   introduced threading 25 years ago...

   Renaming just for that causes churn, but it becomes easier once we 
   have the conversion patches for helpers for explicit uses of PF_ 
   flags.

 - We might want to add set_task_*() helpers as well, to totally 
   encapsulate PF_ uses. Maybe. I dislike how close it is to the 
   existing set_tsk*() methods that manipulate TIF_ flags. The 
   dichotomy between the TIF_ and PF_ space isn't really sensible these 
   days I think on a conceptual level - although merging them is 
   probably not practical due to possibly running out of easy 64-bit 
   word width.

I'll send out a full series if there's no better suggestions for the 
general approach.

Thanks,

	Ingo

============================>
From: Ingo Molnar <mingo@kernel.org>
Date: Sat, 26 Apr 2025 20:00:22 +0200
Subject: [PATCH] sched/core: Introduce task_*() helpers for PF_ flags

Add straightforward PF_ task flag helpers:

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

                |
               \|/
		V

	if (!task_kthread(task))
		...

( Fortunately there's no namespace collision for any of the new
  methods introduced. )

Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 include/linux/sched.h | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index f96ac1982893..ef5a2e98dd9e 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1747,6 +1747,38 @@ extern struct pid *cad_pid;
 #define PF__HOLE__40000000	0x40000000
 #define PF_SUSPEND_TASK		0x80000000      /* This thread called freeze_processes() and should not be frozen */
 
+/*
+ * Helpers for PF_ flags:
+ */
+#define task_vcpu(task)				((task)->flags & PF_VCPU)
+#define task_idle(task)				((task)->flags & PF_IDLE)
+#define task_exiting(task)			((task)->flags & PF_EXITING)
+#define task_postcoredump(task)			((task)->flags & PF_POSTCOREDUMP)
+#define task_io_worker(task)			((task)->flags & PF_IO_WORKER)
+#define task_wq_worker(task)			((task)->flags & PF_WQ_WORKER)
+#define task_forknoexec(task)			((task)->flags & PF_FORKNOEXEC)
+#define task_mce_process(task)			((task)->flags & PF_MCE_PROCESS)
+#define task_superpriv(task)			((task)->flags & PF_SUPERPRIV)
+#define task_dumpcore(task)			((task)->flags & PF_DUMPCORE)
+#define task_signaled(task)			((task)->flags & PF_SIGNALED)
+#define task_memalloc(task)			((task)->flags & PF_MEMALLOC)
+#define task_nproc_exceeded(task)		((task)->flags & PF_NPROC_EXCEEDED)
+#define task_used_math(task)			((task)->flags & PF_USED_MATH)
+#define task_user_worker(task)			((task)->flags & PF_USER_WORKER)
+#define task_nofreeze(task)			((task)->flags & PF_NOFREEZE)
+#define task_kcompactd(task)			((task)->flags & PF_KCOMPACTD)
+#define task_kswapd(task)			((task)->flags & PF_KSWAPD)
+#define task_memalloc_nofs(task)		((task)->flags & PF_MEMALLOC_NOFS)
+#define task_memalloc_noio(task)		((task)->flags & PF_MEMALLOC_NOIO)
+#define task_local_throttle(task)		((task)->flags & PF_LOCAL_THROTTLE)
+#define task_kthread(task)			((task)->flags & PF_KTHREAD)
+#define task_randomize(task)			((task)->flags & PF_RANDOMIZE)
+#define task_no_setaffinity(task)		((task)->flags & PF_NO_SETAFFINITY)
+#define task_mce_early(task)			((task)->flags & PF_MCE_EARLY)
+#define task_memalloc_pin(task)			((task)->flags & PF_MEMALLOC_PIN)
+#define task_block_ts(task)			((task)->flags & PF_BLOCK_TS)
+#define task_suspend_task(task)			((task)->flags & PF_SUSPEND_TASK)
+
 /*
  * Only the _current_ task can read/write to tsk->flags, but other
  * tasks can access tsk->flags in readonly mode for example

Re: [PATCH] sched/core: Introduce task_*() helpers for PF_ flags

[Ingo Molnar]

* Ingo Molnar <mingo@kernel.org> wrote:

>  - We might want to add set_task_*() helpers as well, to totally 
>    encapsulate PF_ uses. Maybe. I dislike how close it is to the 
>    existing set_tsk*() methods that manipulate TIF_ flags. The 
>    dichotomy between the TIF_ and PF_ space isn't really sensible these 
>    days I think on a conceptual level - although merging them is 
>    probably not practical due to possibly running out of easy 64-bit 
>    word width.

And yeah, the TIF_ space is per arch to a substantial degree, and is 
accessed from assembly code, plus is often operated on atomically, 
while the PF_ space is nicely generic and non-atomic - but still we 
could do better to express that these two per task flag spaces are 
rather similar in purpose, instead of this historic 'task/process' 
distinction that isn't actually true.

Thanks,

	Ingo

Re: [PATCH] sched/core: Introduce task_*() helpers for PF_ flags

[Steven Rostedt]

On Sat, 26 Apr 2025 20:42:21 +0200
Ingo Molnar <mingo@kernel.org> wrote:


> > kernel/sched/core.c:    if (!curr->mm || (curr->flags & (PF_EXITING | PF_KTHREAD)) ||
> > kernel/sched/fair.c:    if (!curr->mm || (curr->flags & (PF_EXITING | PF_KTHREAD)) || work->next != work)
> > kernel/trace/bpf_trace.c:                    current->flags & (PF_KTHREAD | PF_EXITING)))
> > kernel/trace/bpf_trace.c:       if (unlikely(task->flags & (PF_KTHREAD | PF_EXITING)))
> > 
> > Maybe we can have a: is_user_exiting_or_kthread() ?  
> 
> No, we don't need is_user_exiting_or_kthread(). At all. Ever. In this 
> universe. Or in any alternative universes. We don't even need 
> is_user_exiting_or_kthread() in horror fiction novels written for 
> kernel developers: there's really a limit to the level of horror that 
> people are able to accept. Sheesh ...

Ingo,

A simple "No we do not need that" would suffice. This isn't 2005 anymore,
where we come up with creative ways to insult each other. We're better now.



> And no, we don't need separate helpers for !task_kthread() et al: the C 
> logical negation unary operator is perfectly readable when placed 
> before a function call or a macro invocation, and a competent Linux 
> kernel developer is expected to recognize it on sight:
> 
> 	if (!task_kthread(task))
> 		...

Not really. I originally tried just having a single "is_kernel_thread()"
where I would use the "!is_kernel_thread()" for user thread, but honestly,
it wasn't much better than the "!(task->flags & PF_KTHREAD)".

And just because it's not a kernel thread, does it mean it will always be a
user space thread? Could it one day also be a guest thread (if we decide to
have such a thing)?

Wanting to know if something is a user space thread, "if (!task_kthread(task))"
seems short sighted. As it assumes that we only have two types of threads.
It may be true today, but may not be the case in the future.

	if (!task_kthread(task))

Still takes a second more to understand that's a user space thread than:

	if (task_user(task))

would.

-- Steve

Re: [PATCH] sched/core: Introduce task_*() helpers for PF_ flags

[Steven Rostedt]

On Sat, 26 Apr 2025 20:42:21 +0200
Ingo Molnar <mingo@kernel.org> wrote:

> I'll send out a full series if there's no better suggestions for the 
> general approach.

Fine, you can take over. I have other things to work on.

Unless you add a task_user() or something similar that makes it very easy
to see that a task is a user thread other than testing if it's not a kernel
thread, it doesn't solve the issue that was my original motivation for my
patches. That is, there's places in the code that needs to only work on
user threads, and it would be nice to quickly see that the if statement is
checking if it is or not.

We have places that check if it's a kernel thread to exit out early:

	if (task_kernel(task))
		goto out;

And places that do something if it's a user thread:

	if (task_user(task))
		// do something special

By explicitly stating "user" in the test, makes that very easy to see,
where as:

	if (task_kernel(task))
		goto out;

and

	if (!task_kernel(task))
		// do something special

makes you have to look a bit harder. The kernel is complex enough, I
believe we should make it easier where there's low hanging fruit to do so.

-- Steve