[PATCH v2] sched,livepatch: Untangle cond_resched() and live-patching

[PATCH v2] sched,livepatch: Untangle cond_resched() and live-patching

[Sebastian Andrzej Siewior]

From: Peter Zijlstra <peterz@infradead.org>

With the goal of deprecating / removing VOLUNTARY preempt, live-patch
needs to stop relying on cond_resched() to make forward progress.

Instead, rely on schedule() with TASK_FREEZABLE set. Just like
live-patching, the freezer needs to be able to stop tasks in a safe /
known state.

Compile tested only.

[bigeasy: use likely() in __klp_sched_try_switch() and update comments]

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
v1…v2: https://lore.kernel.org/all/20250324134909.GA14718@noisy.programming.kicks-ass.net/
  - Updated comments in __klp_sched_try_switch()
  - Replaced unlikely with likely in __klp_sched_try_switch()
  - Dropped RFC

 include/linux/livepatch_sched.h | 14 ++++-----
 include/linux/sched.h           |  6 ----
 kernel/livepatch/transition.c   | 52 ++++++++++-----------------------
 kernel/sched/core.c             | 50 +++++--------------------------
 4 files changed, 29 insertions(+), 93 deletions(-)

diff --git a/include/linux/livepatch_sched.h b/include/linux/livepatch_sched.h
index 013794fb5da08..065c185f27638 100644
--- a/include/linux/livepatch_sched.h
+++ b/include/linux/livepatch_sched.h
@@ -3,27 +3,23 @@
 #define _LINUX_LIVEPATCH_SCHED_H_
 
 #include <linux/jump_label.h>
-#include <linux/static_call_types.h>
+#include <linux/sched.h>
 
 #ifdef CONFIG_LIVEPATCH
 
 void __klp_sched_try_switch(void);
 
-#if !defined(CONFIG_PREEMPT_DYNAMIC) || !defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
-
 DECLARE_STATIC_KEY_FALSE(klp_sched_try_switch_key);
 
-static __always_inline void klp_sched_try_switch(void)
+static __always_inline void klp_sched_try_switch(struct task_struct *curr)
 {
-	if (static_branch_unlikely(&klp_sched_try_switch_key))
+	if (static_branch_unlikely(&klp_sched_try_switch_key) &&
+	    READ_ONCE(curr->__state) & TASK_FREEZABLE)
 		__klp_sched_try_switch();
 }
 
-#endif /* !CONFIG_PREEMPT_DYNAMIC || !CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
-
 #else /* !CONFIG_LIVEPATCH */
-static inline void klp_sched_try_switch(void) {}
-static inline void __klp_sched_try_switch(void) {}
+static inline void klp_sched_try_switch(struct task_struct *curr) {}
 #endif /* CONFIG_LIVEPATCH */
 
 #endif /* _LINUX_LIVEPATCH_SCHED_H_ */
diff --git a/include/linux/sched.h b/include/linux/sched.h
index f96ac19828934..b98195991031c 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -44,7 +44,6 @@
 #include <linux/seqlock_types.h>
 #include <linux/kcsan.h>
 #include <linux/rv.h>
-#include <linux/livepatch_sched.h>
 #include <linux/uidgid_types.h>
 #include <linux/tracepoint-defs.h>
 #include <asm/kmap_size.h>
@@ -2089,9 +2088,6 @@ extern int __cond_resched(void);
 
 #if defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
 
-void sched_dynamic_klp_enable(void);
-void sched_dynamic_klp_disable(void);
-
 DECLARE_STATIC_CALL(cond_resched, __cond_resched);
 
 static __always_inline int _cond_resched(void)
@@ -2112,7 +2108,6 @@ static __always_inline int _cond_resched(void)
 
 static inline int _cond_resched(void)
 {
-	klp_sched_try_switch();
 	return __cond_resched();
 }
 
@@ -2122,7 +2117,6 @@ static inline int _cond_resched(void)
 
 static inline int _cond_resched(void)
 {
-	klp_sched_try_switch();
 	return 0;
 }
 
diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
index ba069459c1017..25b9372a4b66f 100644
--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c
@@ -29,22 +29,13 @@ static unsigned int klp_signals_cnt;
 
 /*
  * When a livepatch is in progress, enable klp stack checking in
- * cond_resched().  This helps CPU-bound kthreads get patched.
+ * schedule().  This helps CPU-bound kthreads get patched.
  */
-#if defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
-
-#define klp_cond_resched_enable() sched_dynamic_klp_enable()
-#define klp_cond_resched_disable() sched_dynamic_klp_disable()
-
-#else /* !CONFIG_PREEMPT_DYNAMIC || !CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
 
 DEFINE_STATIC_KEY_FALSE(klp_sched_try_switch_key);
-EXPORT_SYMBOL(klp_sched_try_switch_key);
 
-#define klp_cond_resched_enable() static_branch_enable(&klp_sched_try_switch_key)
-#define klp_cond_resched_disable() static_branch_disable(&klp_sched_try_switch_key)
-
-#endif /* CONFIG_PREEMPT_DYNAMIC && CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
+#define klp_resched_enable() static_branch_enable(&klp_sched_try_switch_key)
+#define klp_resched_disable() static_branch_disable(&klp_sched_try_switch_key)
 
 /*
  * This work can be performed periodically to finish patching or unpatching any
@@ -365,27 +356,20 @@ static bool klp_try_switch_task(struct task_struct *task)
 
 void __klp_sched_try_switch(void)
 {
+	/*
+	 * This function is called from __schedule() while a context switch is
+	 * about to happen. Preemption is already disabled and klp_mutex
+	 * can't be acquired.
+	 * Disabled preemption is used to prevent racing with other callers of
+	 * klp_try_switch_task(). Thanks to task_call_func() they won't be
+	 * able to switch to this task while it's running.
+	 */
+	lockdep_assert_preemption_disabled();
+
+	/* Make sure current didn't get patched */
 	if (likely(!klp_patch_pending(current)))
 		return;
 
-	/*
-	 * This function is called from cond_resched() which is called in many
-	 * places throughout the kernel.  Using the klp_mutex here might
-	 * deadlock.
-	 *
-	 * Instead, disable preemption to prevent racing with other callers of
-	 * klp_try_switch_task().  Thanks to task_call_func() they won't be
-	 * able to switch this task while it's running.
-	 */
-	preempt_disable();
-
-	/*
-	 * Make sure current didn't get patched between the above check and
-	 * preempt_disable().
-	 */
-	if (unlikely(!klp_patch_pending(current)))
-		goto out;
-
 	/*
 	 * Enforce the order of the TIF_PATCH_PENDING read above and the
 	 * klp_target_state read in klp_try_switch_task().  The corresponding
@@ -395,11 +379,7 @@ void __klp_sched_try_switch(void)
 	smp_rmb();
 
 	klp_try_switch_task(current);
-
-out:
-	preempt_enable();
 }
-EXPORT_SYMBOL(__klp_sched_try_switch);
 
 /*
  * Sends a fake signal to all non-kthread tasks with TIF_PATCH_PENDING set.
@@ -508,7 +488,7 @@ void klp_try_complete_transition(void)
 	}
 
 	/* Done!  Now cleanup the data structures. */
-	klp_cond_resched_disable();
+	klp_resched_disable();
 	patch = klp_transition_patch;
 	klp_complete_transition();
 
@@ -560,7 +540,7 @@ void klp_start_transition(void)
 			set_tsk_thread_flag(task, TIF_PATCH_PENDING);
 	}
 
-	klp_cond_resched_enable();
+	klp_resched_enable();
 
 	klp_signals_cnt = 0;
 }
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index c81cf642dba05..2a973d0e414a3 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -66,6 +66,7 @@
 #include <linux/vtime.h>
 #include <linux/wait_api.h>
 #include <linux/workqueue_api.h>
+#include <linux/livepatch_sched.h>
 
 #ifdef CONFIG_PREEMPT_DYNAMIC
 # ifdef CONFIG_GENERIC_ENTRY
@@ -6668,6 +6669,8 @@ static void __sched notrace __schedule(int sched_mode)
 	if (sched_feat(HRTICK) || sched_feat(HRTICK_DL))
 		hrtick_clear(rq);
 
+	klp_sched_try_switch(prev);
+
 	local_irq_disable();
 	rcu_note_context_switch(preempt);
 
@@ -7328,7 +7331,6 @@ EXPORT_STATIC_CALL_TRAMP(might_resched);
 static DEFINE_STATIC_KEY_FALSE(sk_dynamic_cond_resched);
 int __sched dynamic_cond_resched(void)
 {
-	klp_sched_try_switch();
 	if (!static_branch_unlikely(&sk_dynamic_cond_resched))
 		return 0;
 	return __cond_resched();
@@ -7500,7 +7502,6 @@ int sched_dynamic_mode(const char *str)
 #endif
 
 static DEFINE_MUTEX(sched_dynamic_mutex);
-static bool klp_override;
 
 static void __sched_dynamic_update(int mode)
 {
@@ -7508,8 +7509,7 @@ static void __sched_dynamic_update(int mode)
 	 * Avoid {NONE,VOLUNTARY} -> FULL transitions from ever ending up in
 	 * the ZERO state, which is invalid.
 	 */
-	if (!klp_override)
-		preempt_dynamic_enable(cond_resched);
+	preempt_dynamic_enable(cond_resched);
 	preempt_dynamic_enable(might_resched);
 	preempt_dynamic_enable(preempt_schedule);
 	preempt_dynamic_enable(preempt_schedule_notrace);
@@ -7518,8 +7518,7 @@ static void __sched_dynamic_update(int mode)
 
 	switch (mode) {
 	case preempt_dynamic_none:
-		if (!klp_override)
-			preempt_dynamic_enable(cond_resched);
+		preempt_dynamic_enable(cond_resched);
 		preempt_dynamic_disable(might_resched);
 		preempt_dynamic_disable(preempt_schedule);
 		preempt_dynamic_disable(preempt_schedule_notrace);
@@ -7530,8 +7529,7 @@ static void __sched_dynamic_update(int mode)
 		break;
 
 	case preempt_dynamic_voluntary:
-		if (!klp_override)
-			preempt_dynamic_enable(cond_resched);
+		preempt_dynamic_enable(cond_resched);
 		preempt_dynamic_enable(might_resched);
 		preempt_dynamic_disable(preempt_schedule);
 		preempt_dynamic_disable(preempt_schedule_notrace);
@@ -7542,8 +7540,7 @@ static void __sched_dynamic_update(int mode)
 		break;
 
 	case preempt_dynamic_full:
-		if (!klp_override)
-			preempt_dynamic_disable(cond_resched);
+		preempt_dynamic_disable(cond_resched);
 		preempt_dynamic_disable(might_resched);
 		preempt_dynamic_enable(preempt_schedule);
 		preempt_dynamic_enable(preempt_schedule_notrace);
@@ -7554,8 +7551,7 @@ static void __sched_dynamic_update(int mode)
 		break;
 
 	case preempt_dynamic_lazy:
-		if (!klp_override)
-			preempt_dynamic_disable(cond_resched);
+		preempt_dynamic_disable(cond_resched);
 		preempt_dynamic_disable(might_resched);
 		preempt_dynamic_enable(preempt_schedule);
 		preempt_dynamic_enable(preempt_schedule_notrace);
@@ -7576,36 +7572,6 @@ void sched_dynamic_update(int mode)
 	mutex_unlock(&sched_dynamic_mutex);
 }
 
-#ifdef CONFIG_HAVE_PREEMPT_DYNAMIC_CALL
-
-static int klp_cond_resched(void)
-{
-	__klp_sched_try_switch();
-	return __cond_resched();
-}
-
-void sched_dynamic_klp_enable(void)
-{
-	mutex_lock(&sched_dynamic_mutex);
-
-	klp_override = true;
-	static_call_update(cond_resched, klp_cond_resched);
-
-	mutex_unlock(&sched_dynamic_mutex);
-}
-
-void sched_dynamic_klp_disable(void)
-{
-	mutex_lock(&sched_dynamic_mutex);
-
-	klp_override = false;
-	__sched_dynamic_update(preempt_dynamic_mode);
-
-	mutex_unlock(&sched_dynamic_mutex);
-}
-
-#endif /* CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
-
 static int __init setup_preempt_mode(char *str)
 {
 	int mode = sched_dynamic_mode(str);
-- 
2.49.0

Re: [PATCH v2] sched,livepatch: Untangle cond_resched() and live-patching

[Miroslav Benes]

Hi,

thanks for the updated version.

On Fri, 9 May 2025, Sebastian Andrzej Siewior wrote:

> From: Peter Zijlstra <peterz@infradead.org>
> 
> With the goal of deprecating / removing VOLUNTARY preempt, live-patch
> needs to stop relying on cond_resched() to make forward progress.
> 
> Instead, rely on schedule() with TASK_FREEZABLE set. Just like
> live-patching, the freezer needs to be able to stop tasks in a safe /
> known state.
> 
> Compile tested only.

livepatch selftests pass and I also ran some more.
 
> [bigeasy: use likely() in __klp_sched_try_switch() and update comments]
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

Acked-by: Miroslav Benes <mbenes@suse.cz>

A nit below if there is an another version, otherwise Petr might fix it 
when merging.

> @@ -365,27 +356,20 @@ static bool klp_try_switch_task(struct task_struct *task)
>  
>  void __klp_sched_try_switch(void)
>  {
> +	/*
> +	 * This function is called from __schedule() while a context switch is
> +	 * about to happen. Preemption is already disabled and klp_mutex
> +	 * can't be acquired.
> +	 * Disabled preemption is used to prevent racing with other callers of
> +	 * klp_try_switch_task(). Thanks to task_call_func() they won't be
> +	 * able to switch to this task while it's running.
> +	 */
> +	lockdep_assert_preemption_disabled();
> +
> +	/* Make sure current didn't get patched */
>       if (likely(!klp_patch_pending(current)))
>                return;

This last comment is not precise. If !klp_patch_pending(), there is 
nothing to do. Fast way out. So if it was up to me, I would remove the 
line all together.

Miroslav

Re: [PATCH v2] sched,livepatch: Untangle cond_resched() and live-patching

[Peter Zijlstra]

On Tue, May 13, 2025 at 03:34:50PM +0200, Miroslav Benes wrote:
> Hi,
> 
> thanks for the updated version.
> 
> On Fri, 9 May 2025, Sebastian Andrzej Siewior wrote:
> 
> > From: Peter Zijlstra <peterz@infradead.org>
> > 
> > With the goal of deprecating / removing VOLUNTARY preempt, live-patch
> > needs to stop relying on cond_resched() to make forward progress.
> > 
> > Instead, rely on schedule() with TASK_FREEZABLE set. Just like
> > live-patching, the freezer needs to be able to stop tasks in a safe /
> > known state.
> > 
> > Compile tested only.
> 
> livepatch selftests pass and I also ran some more.
>  
> > [bigeasy: use likely() in __klp_sched_try_switch() and update comments]
> > 
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> 
> Acked-by: Miroslav Benes <mbenes@suse.cz>
> 
> A nit below if there is an another version, otherwise Petr might fix it 
> when merging.

Petr or Peter?

That is, who are we expecting to merge this :-)

Anyway, I've zapped the line in my copy.

> > @@ -365,27 +356,20 @@ static bool klp_try_switch_task(struct task_struct *task)
> >  
> >  void __klp_sched_try_switch(void)
> >  {
> > +	/*
> > +	 * This function is called from __schedule() while a context switch is
> > +	 * about to happen. Preemption is already disabled and klp_mutex
> > +	 * can't be acquired.
> > +	 * Disabled preemption is used to prevent racing with other callers of
> > +	 * klp_try_switch_task(). Thanks to task_call_func() they won't be
> > +	 * able to switch to this task while it's running.
> > +	 */
> > +	lockdep_assert_preemption_disabled();
> > +
> > +	/* Make sure current didn't get patched */
> >       if (likely(!klp_patch_pending(current)))
> >                return;
> 
> This last comment is not precise. If !klp_patch_pending(), there is 
> nothing to do. Fast way out. So if it was up to me, I would remove the 
> line all together.
> 
> Miroslav

Re: [PATCH v2] sched,livepatch: Untangle cond_resched() and live-patching

[Miroslav Benes]

On Tue, 13 May 2025, Peter Zijlstra wrote:

> On Tue, May 13, 2025 at 03:34:50PM +0200, Miroslav Benes wrote:
> > Hi,
> > 
> > thanks for the updated version.
> > 
> > On Fri, 9 May 2025, Sebastian Andrzej Siewior wrote:
> > 
> > > From: Peter Zijlstra <peterz@infradead.org>
> > > 
> > > With the goal of deprecating / removing VOLUNTARY preempt, live-patch
> > > needs to stop relying on cond_resched() to make forward progress.
> > > 
> > > Instead, rely on schedule() with TASK_FREEZABLE set. Just like
> > > live-patching, the freezer needs to be able to stop tasks in a safe /
> > > known state.
> > > 
> > > Compile tested only.
> > 
> > livepatch selftests pass and I also ran some more.
> >  
> > > [bigeasy: use likely() in __klp_sched_try_switch() and update comments]
> > > 
> > > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> > > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> > 
> > Acked-by: Miroslav Benes <mbenes@suse.cz>
> > 
> > A nit below if there is an another version, otherwise Petr might fix it 
> > when merging.
> 
> Petr or Peter?
> 
> That is, who are we expecting to merge this :-)

Petr Mladek if it goes through the live patching tree, you if tip. Feel 
free to pick it up :).

> Anyway, I've zapped the line in my copy.

Thanks!

Miroslav

Re: [PATCH v2] sched,livepatch: Untangle cond_resched() and live-patching

[Josh Poimboeuf]

On Fri, May 09, 2025 at 01:36:59PM +0200, Sebastian Andrzej Siewior wrote:
> From: Peter Zijlstra <peterz@infradead.org>
> 
> With the goal of deprecating / removing VOLUNTARY preempt, live-patch
> needs to stop relying on cond_resched() to make forward progress.
> 
> Instead, rely on schedule() with TASK_FREEZABLE set. Just like
> live-patching, the freezer needs to be able to stop tasks in a safe /
> known state.
> 
> Compile tested only.
> 
> [bigeasy: use likely() in __klp_sched_try_switch() and update comments]
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>

-- 
Josh

Re: [PATCH v2] sched,livepatch: Untangle cond_resched() and live-patching

[Petr Mladek]

On Tue 2025-05-13 15:34:50, Miroslav Benes wrote:
> On Fri, 9 May 2025, Sebastian Andrzej Siewior wrote:
> 
> > From: Peter Zijlstra <peterz@infradead.org>
> > 
> > With the goal of deprecating / removing VOLUNTARY preempt, live-patch
> > needs to stop relying on cond_resched() to make forward progress.
> > 
> > Instead, rely on schedule() with TASK_FREEZABLE set. Just like
> > live-patching, the freezer needs to be able to stop tasks in a safe /
> > known state.
> > 
> > @@ -365,27 +356,20 @@ static bool klp_try_switch_task(struct task_struct *task)
> >  
> >  void __klp_sched_try_switch(void)
> >  {
> > +	/*
> > +	 * This function is called from __schedule() while a context switch is
> > +	 * about to happen. Preemption is already disabled and klp_mutex
> > +	 * can't be acquired.
> > +	 * Disabled preemption is used to prevent racing with other callers of
> > +	 * klp_try_switch_task(). Thanks to task_call_func() they won't be
> > +	 * able to switch to this task while it's running.
> > +	 */
> > +	lockdep_assert_preemption_disabled();
> > +
> > +	/* Make sure current didn't get patched */
> >       if (likely(!klp_patch_pending(current)))
> >                return;
> 
> This last comment is not precise. If !klp_patch_pending(), there is 
> nothing to do. Fast way out. So if it was up to me, I would remove the 
> line all together.

I think that this is not just a speedup. Right below is a read memory
barrier. It says that we need to read TIF_PATCH_PENDING here to
make sure that klp_target_state is correct after the barrier.

Anyway, I agree that the comment is confusing and might be removed.
The comment above the memory barrier might/should be enough.

Best Regards,
Petr

Re: [PATCH v2] sched,livepatch: Untangle cond_resched() and live-patching

[Petr Mladek]

On Tue 2025-05-13 16:05:51, Miroslav Benes wrote:
> On Tue, 13 May 2025, Peter Zijlstra wrote:
> 
> > On Tue, May 13, 2025 at 03:34:50PM +0200, Miroslav Benes wrote:
> > > Hi,
> > > 
> > > thanks for the updated version.
> > > 
> > > On Fri, 9 May 2025, Sebastian Andrzej Siewior wrote:
> > > 
> > > > From: Peter Zijlstra <peterz@infradead.org>
> > > > 
> > > > With the goal of deprecating / removing VOLUNTARY preempt, live-patch
> > > > needs to stop relying on cond_resched() to make forward progress.
> > > > 
> > > > Instead, rely on schedule() with TASK_FREEZABLE set. Just like
> > > > live-patching, the freezer needs to be able to stop tasks in a safe /
> > > > known state.
> > > > 
> > > > Compile tested only.
> > > 
> > > livepatch selftests pass and I also ran some more.
> > >  
> > > > [bigeasy: use likely() in __klp_sched_try_switch() and update comments]
> > > > 
> > > > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> > > > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> > > 
> > > Acked-by: Miroslav Benes <mbenes@suse.cz>
> > > 
> > > A nit below if there is an another version, otherwise Petr might fix it 
> > > when merging.
> > 
> > Petr or Peter?
> > 
> > That is, who are we expecting to merge this :-)
> 
> Petr Mladek if it goes through the live patching tree, you if tip. Feel 
> free to pick it up :).

IMHO, it might be easier when it goes via tip. Peter, feel free to
take it.

The patch does not create any conflict with the klp tree.
But I guess that there might be some dependent patches in tip...

That said, I could take it via the livepatch tree if Peter preferred
it from some reasons.

Anyway, the patch looks good and passes the tests. Feel free to use:

Reviewed-by: Petr Mladek <pmladek@suse.com>
Tested-by: Petr Mladek <pmladek@suse.com>

Best Regards,
Petr

Re: [PATCH v2] sched,livepatch: Untangle cond_resched() and live-patching

[Thomas Gleixner]

On Fri, May 09 2025 at 13:36, Sebastian Andrzej Siewior wrote:
> From: Peter Zijlstra <peterz@infradead.org>
>
> With the goal of deprecating / removing VOLUNTARY preempt, live-patch
> needs to stop relying on cond_resched() to make forward progress.
>
> Instead, rely on schedule() with TASK_FREEZABLE set. Just like
> live-patching, the freezer needs to be able to stop tasks in a safe /
> known state.
>
> Compile tested only.
>
> [bigeasy: use likely() in __klp_sched_try_switch() and update comments]
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

Reviewed-by: Thomas Gleixner <tglx@linutronix.de>

[tip: sched/core] sched,livepatch: Untangle cond_resched() and live-patching

[tip-bot2 for Peter Zijlstra]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     fe2ece0700df81ee1fc91d51d80a1a3f37e59806
Gitweb:        https://git.kernel.org/tip/fe2ece0700df81ee1fc91d51d80a1a3f37e59806
Author:        Peter Zijlstra <peterz@infradead.org>
AuthorDate:    Fri, 09 May 2025 13:36:59 +02:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Wed, 14 May 2025 13:09:50 +02:00

sched,livepatch: Untangle cond_resched() and live-patching

With the goal of deprecating / removing VOLUNTARY preempt, live-patch
needs to stop relying on cond_resched() to make forward progress.

Instead, rely on schedule() with TASK_FREEZABLE set. Just like
live-patching, the freezer needs to be able to stop tasks in a safe /
known state.

[bigeasy: use likely() in __klp_sched_try_switch() and update comments]

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Link: https://lore.kernel.org/r/20250509113659.wkP_HJ5z@linutronix.de
---
 include/linux/livepatch_sched.h | 14 +++------
 include/linux/sched.h           |  6 +----
 kernel/livepatch/transition.c   | 49 ++++++++-----------------------
 kernel/sched/core.c             | 50 +++++---------------------------
 4 files changed, 27 insertions(+), 92 deletions(-)

diff --git a/include/linux/livepatch_sched.h b/include/linux/livepatch_sched.h
index 013794f..065c185 100644
--- a/include/linux/livepatch_sched.h
+++ b/include/linux/livepatch_sched.h
@@ -3,27 +3,23 @@
 #define _LINUX_LIVEPATCH_SCHED_H_
 
 #include <linux/jump_label.h>
-#include <linux/static_call_types.h>
+#include <linux/sched.h>
 
 #ifdef CONFIG_LIVEPATCH
 
 void __klp_sched_try_switch(void);
 
-#if !defined(CONFIG_PREEMPT_DYNAMIC) || !defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
-
 DECLARE_STATIC_KEY_FALSE(klp_sched_try_switch_key);
 
-static __always_inline void klp_sched_try_switch(void)
+static __always_inline void klp_sched_try_switch(struct task_struct *curr)
 {
-	if (static_branch_unlikely(&klp_sched_try_switch_key))
+	if (static_branch_unlikely(&klp_sched_try_switch_key) &&
+	    READ_ONCE(curr->__state) & TASK_FREEZABLE)
 		__klp_sched_try_switch();
 }
 
-#endif /* !CONFIG_PREEMPT_DYNAMIC || !CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
-
 #else /* !CONFIG_LIVEPATCH */
-static inline void klp_sched_try_switch(void) {}
-static inline void __klp_sched_try_switch(void) {}
+static inline void klp_sched_try_switch(struct task_struct *curr) {}
 #endif /* CONFIG_LIVEPATCH */
 
 #endif /* _LINUX_LIVEPATCH_SCHED_H_ */
diff --git a/include/linux/sched.h b/include/linux/sched.h
index f96ac19..b981959 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -44,7 +44,6 @@
 #include <linux/seqlock_types.h>
 #include <linux/kcsan.h>
 #include <linux/rv.h>
-#include <linux/livepatch_sched.h>
 #include <linux/uidgid_types.h>
 #include <linux/tracepoint-defs.h>
 #include <asm/kmap_size.h>
@@ -2089,9 +2088,6 @@ extern int __cond_resched(void);
 
 #if defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
 
-void sched_dynamic_klp_enable(void);
-void sched_dynamic_klp_disable(void);
-
 DECLARE_STATIC_CALL(cond_resched, __cond_resched);
 
 static __always_inline int _cond_resched(void)
@@ -2112,7 +2108,6 @@ static __always_inline int _cond_resched(void)
 
 static inline int _cond_resched(void)
 {
-	klp_sched_try_switch();
 	return __cond_resched();
 }
 
@@ -2122,7 +2117,6 @@ static inline int _cond_resched(void)
 
 static inline int _cond_resched(void)
 {
-	klp_sched_try_switch();
 	return 0;
 }
 
diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
index ba06945..2351a19 100644
--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c
@@ -29,22 +29,13 @@ static unsigned int klp_signals_cnt;
 
 /*
  * When a livepatch is in progress, enable klp stack checking in
- * cond_resched().  This helps CPU-bound kthreads get patched.
+ * schedule().  This helps CPU-bound kthreads get patched.
  */
-#if defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
-
-#define klp_cond_resched_enable() sched_dynamic_klp_enable()
-#define klp_cond_resched_disable() sched_dynamic_klp_disable()
-
-#else /* !CONFIG_PREEMPT_DYNAMIC || !CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
 
 DEFINE_STATIC_KEY_FALSE(klp_sched_try_switch_key);
-EXPORT_SYMBOL(klp_sched_try_switch_key);
 
-#define klp_cond_resched_enable() static_branch_enable(&klp_sched_try_switch_key)
-#define klp_cond_resched_disable() static_branch_disable(&klp_sched_try_switch_key)
-
-#endif /* CONFIG_PREEMPT_DYNAMIC && CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
+#define klp_resched_enable() static_branch_enable(&klp_sched_try_switch_key)
+#define klp_resched_disable() static_branch_disable(&klp_sched_try_switch_key)
 
 /*
  * This work can be performed periodically to finish patching or unpatching any
@@ -365,26 +356,18 @@ static bool klp_try_switch_task(struct task_struct *task)
 
 void __klp_sched_try_switch(void)
 {
-	if (likely(!klp_patch_pending(current)))
-		return;
-
 	/*
-	 * This function is called from cond_resched() which is called in many
-	 * places throughout the kernel.  Using the klp_mutex here might
-	 * deadlock.
-	 *
-	 * Instead, disable preemption to prevent racing with other callers of
-	 * klp_try_switch_task().  Thanks to task_call_func() they won't be
-	 * able to switch this task while it's running.
+	 * This function is called from __schedule() while a context switch is
+	 * about to happen. Preemption is already disabled and klp_mutex
+	 * can't be acquired.
+	 * Disabled preemption is used to prevent racing with other callers of
+	 * klp_try_switch_task(). Thanks to task_call_func() they won't be
+	 * able to switch to this task while it's running.
 	 */
-	preempt_disable();
+	lockdep_assert_preemption_disabled();
 
-	/*
-	 * Make sure current didn't get patched between the above check and
-	 * preempt_disable().
-	 */
-	if (unlikely(!klp_patch_pending(current)))
-		goto out;
+	if (likely(!klp_patch_pending(current)))
+		return;
 
 	/*
 	 * Enforce the order of the TIF_PATCH_PENDING read above and the
@@ -395,11 +378,7 @@ void __klp_sched_try_switch(void)
 	smp_rmb();
 
 	klp_try_switch_task(current);
-
-out:
-	preempt_enable();
 }
-EXPORT_SYMBOL(__klp_sched_try_switch);
 
 /*
  * Sends a fake signal to all non-kthread tasks with TIF_PATCH_PENDING set.
@@ -508,7 +487,7 @@ void klp_try_complete_transition(void)
 	}
 
 	/* Done!  Now cleanup the data structures. */
-	klp_cond_resched_disable();
+	klp_resched_disable();
 	patch = klp_transition_patch;
 	klp_complete_transition();
 
@@ -560,7 +539,7 @@ void klp_start_transition(void)
 			set_tsk_thread_flag(task, TIF_PATCH_PENDING);
 	}
 
-	klp_cond_resched_enable();
+	klp_resched_enable();
 
 	klp_signals_cnt = 0;
 }
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index a3507ed..bece0ba 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -66,6 +66,7 @@
 #include <linux/vtime.h>
 #include <linux/wait_api.h>
 #include <linux/workqueue_api.h>
+#include <linux/livepatch_sched.h>
 
 #ifdef CONFIG_PREEMPT_DYNAMIC
 # ifdef CONFIG_GENERIC_ENTRY
@@ -6676,6 +6677,8 @@ static void __sched notrace __schedule(int sched_mode)
 	if (sched_feat(HRTICK) || sched_feat(HRTICK_DL))
 		hrtick_clear(rq);
 
+	klp_sched_try_switch(prev);
+
 	local_irq_disable();
 	rcu_note_context_switch(preempt);
 
@@ -7336,7 +7339,6 @@ EXPORT_STATIC_CALL_TRAMP(might_resched);
 static DEFINE_STATIC_KEY_FALSE(sk_dynamic_cond_resched);
 int __sched dynamic_cond_resched(void)
 {
-	klp_sched_try_switch();
 	if (!static_branch_unlikely(&sk_dynamic_cond_resched))
 		return 0;
 	return __cond_resched();
@@ -7508,7 +7510,6 @@ int sched_dynamic_mode(const char *str)
 #endif
 
 static DEFINE_MUTEX(sched_dynamic_mutex);
-static bool klp_override;
 
 static void __sched_dynamic_update(int mode)
 {
@@ -7516,8 +7517,7 @@ static void __sched_dynamic_update(int mode)
 	 * Avoid {NONE,VOLUNTARY} -> FULL transitions from ever ending up in
 	 * the ZERO state, which is invalid.
 	 */
-	if (!klp_override)
-		preempt_dynamic_enable(cond_resched);
+	preempt_dynamic_enable(cond_resched);
 	preempt_dynamic_enable(might_resched);
 	preempt_dynamic_enable(preempt_schedule);
 	preempt_dynamic_enable(preempt_schedule_notrace);
@@ -7526,8 +7526,7 @@ static void __sched_dynamic_update(int mode)
 
 	switch (mode) {
 	case preempt_dynamic_none:
-		if (!klp_override)
-			preempt_dynamic_enable(cond_resched);
+		preempt_dynamic_enable(cond_resched);
 		preempt_dynamic_disable(might_resched);
 		preempt_dynamic_disable(preempt_schedule);
 		preempt_dynamic_disable(preempt_schedule_notrace);
@@ -7538,8 +7537,7 @@ static void __sched_dynamic_update(int mode)
 		break;
 
 	case preempt_dynamic_voluntary:
-		if (!klp_override)
-			preempt_dynamic_enable(cond_resched);
+		preempt_dynamic_enable(cond_resched);
 		preempt_dynamic_enable(might_resched);
 		preempt_dynamic_disable(preempt_schedule);
 		preempt_dynamic_disable(preempt_schedule_notrace);
@@ -7550,8 +7548,7 @@ static void __sched_dynamic_update(int mode)
 		break;
 
 	case preempt_dynamic_full:
-		if (!klp_override)
-			preempt_dynamic_disable(cond_resched);
+		preempt_dynamic_disable(cond_resched);
 		preempt_dynamic_disable(might_resched);
 		preempt_dynamic_enable(preempt_schedule);
 		preempt_dynamic_enable(preempt_schedule_notrace);
@@ -7562,8 +7559,7 @@ static void __sched_dynamic_update(int mode)
 		break;
 
 	case preempt_dynamic_lazy:
-		if (!klp_override)
-			preempt_dynamic_disable(cond_resched);
+		preempt_dynamic_disable(cond_resched);
 		preempt_dynamic_disable(might_resched);
 		preempt_dynamic_enable(preempt_schedule);
 		preempt_dynamic_enable(preempt_schedule_notrace);
@@ -7584,36 +7580,6 @@ void sched_dynamic_update(int mode)
 	mutex_unlock(&sched_dynamic_mutex);
 }
 
-#ifdef CONFIG_HAVE_PREEMPT_DYNAMIC_CALL
-
-static int klp_cond_resched(void)
-{
-	__klp_sched_try_switch();
-	return __cond_resched();
-}
-
-void sched_dynamic_klp_enable(void)
-{
-	mutex_lock(&sched_dynamic_mutex);
-
-	klp_override = true;
-	static_call_update(cond_resched, klp_cond_resched);
-
-	mutex_unlock(&sched_dynamic_mutex);
-}
-
-void sched_dynamic_klp_disable(void)
-{
-	mutex_lock(&sched_dynamic_mutex);
-
-	klp_override = false;
-	__sched_dynamic_update(preempt_dynamic_mode);
-
-	mutex_unlock(&sched_dynamic_mutex);
-}
-
-#endif /* CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
-
 static int __init setup_preempt_mode(char *str)
 {
 	int mode = sched_dynamic_mode(str);

Re: [PATCH v2] sched,livepatch: Untangle cond_resched() and live-patching

[Peter Zijlstra]

On Wed, May 14, 2025 at 11:51:44AM +0200, Petr Mladek wrote:

> IMHO, it might be easier when it goes via tip. Peter, feel free to
> take it.

Done!

> Reviewed-by: Petr Mladek <pmladek@suse.com>
> Tested-by: Petr Mladek <pmladek@suse.com>

For some reason b4 didn't pick up these tags, added them manually and
force pushed it again.

[tip: sched/core] sched,livepatch: Untangle cond_resched() and live-patching

[tip-bot2 for Peter Zijlstra]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     676e8cf70cb0533e1118e29898c9a9c33ae3a10f
Gitweb:        https://git.kernel.org/tip/676e8cf70cb0533e1118e29898c9a9c33ae3a10f
Author:        Peter Zijlstra <peterz@infradead.org>
AuthorDate:    Fri, 09 May 2025 13:36:59 +02:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Wed, 14 May 2025 13:16:24 +02:00

sched,livepatch: Untangle cond_resched() and live-patching

With the goal of deprecating / removing VOLUNTARY preempt, live-patch
needs to stop relying on cond_resched() to make forward progress.

Instead, rely on schedule() with TASK_FREEZABLE set. Just like
live-patching, the freezer needs to be able to stop tasks in a safe /
known state.

[bigeasy: use likely() in __klp_sched_try_switch() and update comments]

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Tested-by: Petr Mladek <pmladek@suse.com>
Tested-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Link: https://lore.kernel.org/r/20250509113659.wkP_HJ5z@linutronix.de
---
 include/linux/livepatch_sched.h | 14 +++------
 include/linux/sched.h           |  6 +----
 kernel/livepatch/transition.c   | 49 ++++++++-----------------------
 kernel/sched/core.c             | 50 +++++---------------------------
 4 files changed, 27 insertions(+), 92 deletions(-)

diff --git a/include/linux/livepatch_sched.h b/include/linux/livepatch_sched.h
index 013794f..065c185 100644
--- a/include/linux/livepatch_sched.h
+++ b/include/linux/livepatch_sched.h
@@ -3,27 +3,23 @@
 #define _LINUX_LIVEPATCH_SCHED_H_
 
 #include <linux/jump_label.h>
-#include <linux/static_call_types.h>
+#include <linux/sched.h>
 
 #ifdef CONFIG_LIVEPATCH
 
 void __klp_sched_try_switch(void);
 
-#if !defined(CONFIG_PREEMPT_DYNAMIC) || !defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
-
 DECLARE_STATIC_KEY_FALSE(klp_sched_try_switch_key);
 
-static __always_inline void klp_sched_try_switch(void)
+static __always_inline void klp_sched_try_switch(struct task_struct *curr)
 {
-	if (static_branch_unlikely(&klp_sched_try_switch_key))
+	if (static_branch_unlikely(&klp_sched_try_switch_key) &&
+	    READ_ONCE(curr->__state) & TASK_FREEZABLE)
 		__klp_sched_try_switch();
 }
 
-#endif /* !CONFIG_PREEMPT_DYNAMIC || !CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
-
 #else /* !CONFIG_LIVEPATCH */
-static inline void klp_sched_try_switch(void) {}
-static inline void __klp_sched_try_switch(void) {}
+static inline void klp_sched_try_switch(struct task_struct *curr) {}
 #endif /* CONFIG_LIVEPATCH */
 
 #endif /* _LINUX_LIVEPATCH_SCHED_H_ */
diff --git a/include/linux/sched.h b/include/linux/sched.h
index f96ac19..b981959 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -44,7 +44,6 @@
 #include <linux/seqlock_types.h>
 #include <linux/kcsan.h>
 #include <linux/rv.h>
-#include <linux/livepatch_sched.h>
 #include <linux/uidgid_types.h>
 #include <linux/tracepoint-defs.h>
 #include <asm/kmap_size.h>
@@ -2089,9 +2088,6 @@ extern int __cond_resched(void);
 
 #if defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
 
-void sched_dynamic_klp_enable(void);
-void sched_dynamic_klp_disable(void);
-
 DECLARE_STATIC_CALL(cond_resched, __cond_resched);
 
 static __always_inline int _cond_resched(void)
@@ -2112,7 +2108,6 @@ static __always_inline int _cond_resched(void)
 
 static inline int _cond_resched(void)
 {
-	klp_sched_try_switch();
 	return __cond_resched();
 }
 
@@ -2122,7 +2117,6 @@ static inline int _cond_resched(void)
 
 static inline int _cond_resched(void)
 {
-	klp_sched_try_switch();
 	return 0;
 }
 
diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
index ba06945..2351a19 100644
--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c
@@ -29,22 +29,13 @@ static unsigned int klp_signals_cnt;
 
 /*
  * When a livepatch is in progress, enable klp stack checking in
- * cond_resched().  This helps CPU-bound kthreads get patched.
+ * schedule().  This helps CPU-bound kthreads get patched.
  */
-#if defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
-
-#define klp_cond_resched_enable() sched_dynamic_klp_enable()
-#define klp_cond_resched_disable() sched_dynamic_klp_disable()
-
-#else /* !CONFIG_PREEMPT_DYNAMIC || !CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
 
 DEFINE_STATIC_KEY_FALSE(klp_sched_try_switch_key);
-EXPORT_SYMBOL(klp_sched_try_switch_key);
 
-#define klp_cond_resched_enable() static_branch_enable(&klp_sched_try_switch_key)
-#define klp_cond_resched_disable() static_branch_disable(&klp_sched_try_switch_key)
-
-#endif /* CONFIG_PREEMPT_DYNAMIC && CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
+#define klp_resched_enable() static_branch_enable(&klp_sched_try_switch_key)
+#define klp_resched_disable() static_branch_disable(&klp_sched_try_switch_key)
 
 /*
  * This work can be performed periodically to finish patching or unpatching any
@@ -365,26 +356,18 @@ static bool klp_try_switch_task(struct task_struct *task)
 
 void __klp_sched_try_switch(void)
 {
-	if (likely(!klp_patch_pending(current)))
-		return;
-
 	/*
-	 * This function is called from cond_resched() which is called in many
-	 * places throughout the kernel.  Using the klp_mutex here might
-	 * deadlock.
-	 *
-	 * Instead, disable preemption to prevent racing with other callers of
-	 * klp_try_switch_task().  Thanks to task_call_func() they won't be
-	 * able to switch this task while it's running.
+	 * This function is called from __schedule() while a context switch is
+	 * about to happen. Preemption is already disabled and klp_mutex
+	 * can't be acquired.
+	 * Disabled preemption is used to prevent racing with other callers of
+	 * klp_try_switch_task(). Thanks to task_call_func() they won't be
+	 * able to switch to this task while it's running.
 	 */
-	preempt_disable();
+	lockdep_assert_preemption_disabled();
 
-	/*
-	 * Make sure current didn't get patched between the above check and
-	 * preempt_disable().
-	 */
-	if (unlikely(!klp_patch_pending(current)))
-		goto out;
+	if (likely(!klp_patch_pending(current)))
+		return;
 
 	/*
 	 * Enforce the order of the TIF_PATCH_PENDING read above and the
@@ -395,11 +378,7 @@ void __klp_sched_try_switch(void)
 	smp_rmb();
 
 	klp_try_switch_task(current);
-
-out:
-	preempt_enable();
 }
-EXPORT_SYMBOL(__klp_sched_try_switch);
 
 /*
  * Sends a fake signal to all non-kthread tasks with TIF_PATCH_PENDING set.
@@ -508,7 +487,7 @@ void klp_try_complete_transition(void)
 	}
 
 	/* Done!  Now cleanup the data structures. */
-	klp_cond_resched_disable();
+	klp_resched_disable();
 	patch = klp_transition_patch;
 	klp_complete_transition();
 
@@ -560,7 +539,7 @@ void klp_start_transition(void)
 			set_tsk_thread_flag(task, TIF_PATCH_PENDING);
 	}
 
-	klp_cond_resched_enable();
+	klp_resched_enable();
 
 	klp_signals_cnt = 0;
 }
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index a3507ed..bece0ba 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -66,6 +66,7 @@
 #include <linux/vtime.h>
 #include <linux/wait_api.h>
 #include <linux/workqueue_api.h>
+#include <linux/livepatch_sched.h>
 
 #ifdef CONFIG_PREEMPT_DYNAMIC
 # ifdef CONFIG_GENERIC_ENTRY
@@ -6676,6 +6677,8 @@ static void __sched notrace __schedule(int sched_mode)
 	if (sched_feat(HRTICK) || sched_feat(HRTICK_DL))
 		hrtick_clear(rq);
 
+	klp_sched_try_switch(prev);
+
 	local_irq_disable();
 	rcu_note_context_switch(preempt);
 
@@ -7336,7 +7339,6 @@ EXPORT_STATIC_CALL_TRAMP(might_resched);
 static DEFINE_STATIC_KEY_FALSE(sk_dynamic_cond_resched);
 int __sched dynamic_cond_resched(void)
 {
-	klp_sched_try_switch();
 	if (!static_branch_unlikely(&sk_dynamic_cond_resched))
 		return 0;
 	return __cond_resched();
@@ -7508,7 +7510,6 @@ int sched_dynamic_mode(const char *str)
 #endif
 
 static DEFINE_MUTEX(sched_dynamic_mutex);
-static bool klp_override;
 
 static void __sched_dynamic_update(int mode)
 {
@@ -7516,8 +7517,7 @@ static void __sched_dynamic_update(int mode)
 	 * Avoid {NONE,VOLUNTARY} -> FULL transitions from ever ending up in
 	 * the ZERO state, which is invalid.
 	 */
-	if (!klp_override)
-		preempt_dynamic_enable(cond_resched);
+	preempt_dynamic_enable(cond_resched);
 	preempt_dynamic_enable(might_resched);
 	preempt_dynamic_enable(preempt_schedule);
 	preempt_dynamic_enable(preempt_schedule_notrace);
@@ -7526,8 +7526,7 @@ static void __sched_dynamic_update(int mode)
 
 	switch (mode) {
 	case preempt_dynamic_none:
-		if (!klp_override)
-			preempt_dynamic_enable(cond_resched);
+		preempt_dynamic_enable(cond_resched);
 		preempt_dynamic_disable(might_resched);
 		preempt_dynamic_disable(preempt_schedule);
 		preempt_dynamic_disable(preempt_schedule_notrace);
@@ -7538,8 +7537,7 @@ static void __sched_dynamic_update(int mode)
 		break;
 
 	case preempt_dynamic_voluntary:
-		if (!klp_override)
-			preempt_dynamic_enable(cond_resched);
+		preempt_dynamic_enable(cond_resched);
 		preempt_dynamic_enable(might_resched);
 		preempt_dynamic_disable(preempt_schedule);
 		preempt_dynamic_disable(preempt_schedule_notrace);
@@ -7550,8 +7548,7 @@ static void __sched_dynamic_update(int mode)
 		break;
 
 	case preempt_dynamic_full:
-		if (!klp_override)
-			preempt_dynamic_disable(cond_resched);
+		preempt_dynamic_disable(cond_resched);
 		preempt_dynamic_disable(might_resched);
 		preempt_dynamic_enable(preempt_schedule);
 		preempt_dynamic_enable(preempt_schedule_notrace);
@@ -7562,8 +7559,7 @@ static void __sched_dynamic_update(int mode)
 		break;
 
 	case preempt_dynamic_lazy:
-		if (!klp_override)
-			preempt_dynamic_disable(cond_resched);
+		preempt_dynamic_disable(cond_resched);
 		preempt_dynamic_disable(might_resched);
 		preempt_dynamic_enable(preempt_schedule);
 		preempt_dynamic_enable(preempt_schedule_notrace);
@@ -7584,36 +7580,6 @@ void sched_dynamic_update(int mode)
 	mutex_unlock(&sched_dynamic_mutex);
 }
 
-#ifdef CONFIG_HAVE_PREEMPT_DYNAMIC_CALL
-
-static int klp_cond_resched(void)
-{
-	__klp_sched_try_switch();
-	return __cond_resched();
-}
-
-void sched_dynamic_klp_enable(void)
-{
-	mutex_lock(&sched_dynamic_mutex);
-
-	klp_override = true;
-	static_call_update(cond_resched, klp_cond_resched);
-
-	mutex_unlock(&sched_dynamic_mutex);
-}
-
-void sched_dynamic_klp_disable(void)
-{
-	mutex_lock(&sched_dynamic_mutex);
-
-	klp_override = false;
-	__sched_dynamic_update(preempt_dynamic_mode);
-
-	mutex_unlock(&sched_dynamic_mutex);
-}
-
-#endif /* CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
-
 static int __init setup_preempt_mode(char *str)
 {
 	int mode = sched_dynamic_mode(str);