Merge tag 'sched-core-2026-02-09' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull scheduler updates from Ingo Molnar:
 "Scheduler Kconfig space updates:

   - Further consolidate configurable preemption modes (Peter Zijlstra)

     Reduce the number of architectures that are allowed to offer
     PREEMPT_NONE and PREEMPT_VOLUNTARY, reducing the number of
     preemption models from four to just two: 'full' and 'lazy' on
     up-to-date architectures (arm64, loongarch, powerpc, riscv, s390,
     x86).

     None and voluntary are only available as legacy features on
     platforms that don't implement lazy preemption yet, or which don't
     even support preemption.

     The goal is to eventually remove cond_resched() and voluntary
     preemption altogether.

  RSEQ based 'scheduler time slice extension' support (Thomas Gleixner
  and Peter Zijlstra):

  This allows a thread to request a time slice extension when it enters
  a critical section to avoid contention on a resource when the thread
  is scheduled out inside of the critical section.

   - Add fields and constants for time slice extension
   - Provide static branch for time slice extensions
   - Add statistics for time slice extensions
   - Add prctl() to enable time slice extensions
   - Implement sys_rseq_slice_yield()
   - Implement syscall entry work for time slice extensions
   - Implement time slice extension enforcement timer
   - Reset slice extension when scheduled
   - Implement rseq_grant_slice_extension()
   - entry: Hook up rseq time slice extension
   - selftests: Implement time slice extension test
   - Allow registering RSEQ with slice extension
   - Move slice_ext_nsec to debugfs
   - Lower default slice extension
   - selftests/rseq: Add rseq slice histogram script

  Scheduler performance/scalability improvements:

   - Update rq->avg_idle when a task is moved to an idle CPU, which
     improves the scalability of various workloads (Shubhang Kaushik)

   - Reorder fields in 'struct rq' for better caching (Blake Jones)

   - Fair scheduler SMP NOHZ balancing code speedups (Shrikanth Hegde):
      - Move checking for nohz cpus after time check
      - Change likelyhood of nohz.nr_cpus
      - Remove nohz.nr_cpus and use weight of cpumask instead

   - Avoid false sharing for sched_clock_irqtime (Wangyang Guo)

   - Cleanups (Yury Norov):
      - Drop useless cpumask_empty() in find_energy_efficient_cpu()
      - Simplify task_numa_find_cpu()
      - Use cpumask_weight_and() in sched_balance_find_dst_group()

  DL scheduler updates:

   - Add a deadline server for sched_ext tasks (by Andrea Righi and Joel
     Fernandes, with fixes by Peter Zijlstra)

  RT scheduler updates:

   - Skip currently executing CPU in rto_next_cpu() (Chen Jinghuang)

  Entry code updates and performance improvements (Jinjie Ruan)

  This is part of the scheduler tree in this cycle due to inter-
  dependencies with the RSEQ based time slice extension work:

    - Remove unused syscall argument from syscall_trace_enter()
    - Rework syscall_exit_to_user_mode_work() for architecture reuse
    - Add arch_ptrace_report_syscall_entry/exit()
    - Inline syscall_exit_work() and syscall_trace_enter()

  Scheduler core updates (Peter Zijlstra):

   - Rework sched_class::wakeup_preempt() and rq_modified_*()
   - Avoid rq->lock bouncing in sched_balance_newidle()
   - Rename rcu_dereference_check_sched_domain() =>
            rcu_dereference_sched_domain()
   - <linux/compiler_types.h>: Add the __signed_scalar_typeof() helper

  Fair scheduler updates/refactoring (Peter Zijlstra and Ingo Molnar):

   - Fold the sched_avg update
   - Change rcu_dereference_check_sched_domain() to rcu-sched
   - Switch to rcu_dereference_all()
   - Remove superfluous rcu_read_lock()
   - Limit hrtick work
   - Join two #ifdef CONFIG_FAIR_GROUP_SCHED blocks
   - Clean up comments in 'struct cfs_rq'
   - Separate se->vlag from se->vprot
   - Rename cfs_rq::avg_load to cfs_rq::sum_weight
   - Rename cfs_rq::avg_vruntime to ::sum_w_vruntime & helper functions
   - Introduce and use the vruntime_cmp() and vruntime_op() wrappers for
     wrapped-signed aritmetics
   - Sort out 'blocked_load*' namespace noise

  Scheduler debugging code updates:

   - Export hidden tracepoints to modules (Gabriele Monaco)

   - Convert copy_from_user() + kstrtouint() to kstrtouint_from_user()
     (Fushuai Wang)

   - Add assertions to QUEUE_CLASS (Peter Zijlstra)

   - hrtimer: Fix tracing oddity (Thomas Gleixner)

  Misc fixes and cleanups:

   - Re-evaluate scheduling when migrating queued tasks out of throttled
     cgroups (Zicheng Qu)

   - Remove task_struct->faults_disabled_mapping (Christoph Hellwig)

   - Fix math notation errors in avg_vruntime comment (Zhan Xusheng)

   - sched/cpufreq: Use %pe format for PTR_ERR() printing
     (zenghongling)"

* tag 'sched-core-2026-02-09' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (64 commits)
  sched: Re-evaluate scheduling when migrating queued tasks out of throttled cgroups
  sched/cpufreq: Use %pe format for PTR_ERR() printing
  sched/rt: Skip currently executing CPU in rto_next_cpu()
  sched/clock: Avoid false sharing for sched_clock_irqtime
  selftests/sched_ext: Add test for DL server total_bw consistency
  selftests/sched_ext: Add test for sched_ext dl_server
  sched/debug: Fix dl_server (re)start conditions
  sched/debug: Add support to change sched_ext server params
  sched_ext: Add a DL server for sched_ext tasks
  sched/debug: Stop and start server based on if it was active
  sched/debug: Fix updating of ppos on server write ops
  sched/deadline: Clear the defer params
  entry: Inline syscall_exit_work() and syscall_trace_enter()
  entry: Add arch_ptrace_report_syscall_entry/exit()
  entry: Rework syscall_exit_to_user_mode_work() for architecture reuse
  entry: Remove unused syscall argument from syscall_trace_enter()
  sched: remove task_struct->faults_disabled_mapping
  sched: Update rq->avg_idle when a task is moved to an idle CPU
  selftests/rseq: Add rseq slice histogram script
  hrtimer: Fix trace oddity
  ...

4 files changed, 35 insertions, 100 deletions

diff --git a/kernel/entry/common.c b/kernel/entry/common.c
index 5c792b30c58a..9ef63e414791 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -17,6 +17,27 @@ void __weak arch_do_signal_or_restart(struct pt_regs *regs) { }
 #define EXIT_TO_USER_MODE_WORK_LOOP	(EXIT_TO_USER_MODE_WORK)
 #endif
 
+/* TIF bits, which prevent a time slice extension. */
+#ifdef CONFIG_PREEMPT_RT
+/*
+ * Since rseq slice ext has a direct correlation to the worst case
+ * scheduling latency (schedule is delayed after all), only have it affect
+ * LAZY reschedules on PREEMPT_RT for now.
+ *
+ * However, since this delay is only applicable to userspace, a value
+ * for rseq_slice_extension_nsec that is strictly less than the worst case
+ * kernel space preempt_disable() region, should mean the scheduling latency
+ * is not affected, even for !LAZY.
+ *
+ * However, since this value depends on the hardware at hand, it cannot be
+ * pre-determined in any sensible way. Hence punt on this problem for now.
+ */
+# define TIF_SLICE_EXT_SCHED	(_TIF_NEED_RESCHED_LAZY)
+#else
+# define TIF_SLICE_EXT_SCHED	(_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY)
+#endif
+#define TIF_SLICE_EXT_DENY	(EXIT_TO_USER_MODE_WORK & ~TIF_SLICE_EXT_SCHED)
+
 static __always_inline unsigned long __exit_to_user_mode_loop(struct pt_regs *regs,
 							      unsigned long ti_work)
 {
@@ -28,8 +49,10 @@ static __always_inline unsigned long __exit_to_user_mode_loop(struct pt_regs *re
 
 		local_irq_enable_exit_to_user(ti_work);
 
-		if (ti_work & (_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY))
-			schedule();
+		if (ti_work & (_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY)) {
+			if (!rseq_grant_slice_extension(ti_work & TIF_SLICE_EXT_DENY))
+				schedule();
+		}
 
 		if (ti_work & _TIF_UPROBE)
 			uprobe_notify_resume(regs);
diff --git a/kernel/entry/common.h b/kernel/entry/common.h
deleted file mode 100644
index f6e6d02f07fe..000000000000
--- a/kernel/entry/common.h
+++ /dev/null
@@ -1,7 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0 */
-#ifndef _COMMON_H
-#define _COMMON_H
-
-bool syscall_user_dispatch(struct pt_regs *regs);
-
-#endif
diff --git a/kernel/entry/syscall-common.c b/kernel/entry/syscall-common.c
index 940a597ded40..cd4967a9c53e 100644
--- a/kernel/entry/syscall-common.c
+++ b/kernel/entry/syscall-common.c
@@ -1,104 +1,23 @@
 // SPDX-License-Identifier: GPL-2.0
 
-#include <linux/audit.h>
 #include <linux/entry-common.h>
-#include "common.h"
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/syscalls.h>
 
-static inline void syscall_enter_audit(struct pt_regs *regs, long syscall)
-{
-	if (unlikely(audit_context())) {
-		unsigned long args[6];
-
-		syscall_get_arguments(current, regs, args);
-		audit_syscall_entry(syscall, args[0], args[1], args[2], args[3]);
-	}
-}
+/* Out of line to prevent tracepoint code duplication */
 
-long syscall_trace_enter(struct pt_regs *regs, long syscall,
-				unsigned long work)
+long trace_syscall_enter(struct pt_regs *regs, long syscall)
 {
-	long ret = 0;
-
+	trace_sys_enter(regs, syscall);
 	/*
-	 * Handle Syscall User Dispatch.  This must comes first, since
-	 * the ABI here can be something that doesn't make sense for
-	 * other syscall_work features.
+	 * Probes or BPF hooks in the tracepoint may have changed the
+	 * system call number. Reread it.
 	 */
-	if (work & SYSCALL_WORK_SYSCALL_USER_DISPATCH) {
-		if (syscall_user_dispatch(regs))
-			return -1L;
-	}
-
-	/* Handle ptrace */
-	if (work & (SYSCALL_WORK_SYSCALL_TRACE | SYSCALL_WORK_SYSCALL_EMU)) {
-		ret = ptrace_report_syscall_entry(regs);
-		if (ret || (work & SYSCALL_WORK_SYSCALL_EMU))
-			return -1L;
-	}
-
-	/* Do seccomp after ptrace, to catch any tracer changes. */
-	if (work & SYSCALL_WORK_SECCOMP) {
-		ret = __secure_computing();
-		if (ret == -1L)
-			return ret;
-	}
-
-	/* Either of the above might have changed the syscall number */
-	syscall = syscall_get_nr(current, regs);
-
-	if (unlikely(work & SYSCALL_WORK_SYSCALL_TRACEPOINT)) {
-		trace_sys_enter(regs, syscall);
-		/*
-		 * Probes or BPF hooks in the tracepoint may have changed the
-		 * system call number as well.
-		 */
-		syscall = syscall_get_nr(current, regs);
-	}
-
-	syscall_enter_audit(regs, syscall);
-
-	return ret ? : syscall;
+	return syscall_get_nr(current, regs);
 }
 
-/*
- * If SYSCALL_EMU is set, then the only reason to report is when
- * SINGLESTEP is set (i.e. PTRACE_SYSEMU_SINGLESTEP).  This syscall
- * instruction has been already reported in syscall_enter_from_user_mode().
- */
-static inline bool report_single_step(unsigned long work)
+void trace_syscall_exit(struct pt_regs *regs, long ret)
 {
-	if (work & SYSCALL_WORK_SYSCALL_EMU)
-		return false;
-
-	return work & SYSCALL_WORK_SYSCALL_EXIT_TRAP;
-}
-
-void syscall_exit_work(struct pt_regs *regs, unsigned long work)
-{
-	bool step;
-
-	/*
-	 * If the syscall was rolled back due to syscall user dispatching,
-	 * then the tracers below are not invoked for the same reason as
-	 * the entry side was not invoked in syscall_trace_enter(): The ABI
-	 * of these syscalls is unknown.
-	 */
-	if (work & SYSCALL_WORK_SYSCALL_USER_DISPATCH) {
-		if (unlikely(current->syscall_dispatch.on_dispatch)) {
-			current->syscall_dispatch.on_dispatch = false;
-			return;
-		}
-	}
-
-	audit_syscall_exit(regs);
-
-	if (work & SYSCALL_WORK_SYSCALL_TRACEPOINT)
-		trace_sys_exit(regs, syscall_get_return_value(current, regs));
-
-	step = report_single_step(work);
-	if (step || work & SYSCALL_WORK_SYSCALL_TRACE)
-		ptrace_report_syscall_exit(regs, step);
+	trace_sys_exit(regs, ret);
 }
diff --git a/kernel/entry/syscall_user_dispatch.c b/kernel/entry/syscall_user_dispatch.c
index a9055eccb27e..d89dffcc2d64 100644
--- a/kernel/entry/syscall_user_dispatch.c
+++ b/kernel/entry/syscall_user_dispatch.c
@@ -2,6 +2,8 @@
 /*
  * Copyright (C) 2020 Collabora Ltd.
  */
+
+#include <linux/entry-common.h>
 #include <linux/sched.h>
 #include <linux/prctl.h>
 #include <linux/ptrace.h>
@@ -15,8 +17,6 @@
 
 #include <asm/syscall.h>
 
-#include "common.h"
-
 static void trigger_sigsys(struct pt_regs *regs)
 {
 	struct kernel_siginfo info;