Merge 0401bbf56d into baeb9a7d8b

After twenty years of development we finally reached the point to enable
   PREEMPT_RT support in the mainline kernel.
 
   All prerequisites are merged, so enable it on the supported architectures
   ARM64, RISCV and X86(32/64-bit).
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Merge tag 'sched-rt-2024-09-17' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull RT enablement from Thomas Gleixner:
 "Enable PREEMPT_RT on supported architectures:

  After twenty years of development we finally reached the point to
  enable PREEMPT_RT support in the mainline kernel.

  All prerequisites are merged, so enable it on the supported
  architectures ARM64, RISCV and X86(32/64-bit)"

* tag 'sched-rt-2024-09-17' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  riscv: Allow to enable PREEMPT_RT.
  arm64: Allow to enable PREEMPT_RT.
  x86: Allow to enable PREEMPT_RT.

arch/arm64/Kconfig

@@ -101,6 +101,7 @@ config ARM64
 	select ARCH_SUPPORTS_NUMA_BALANCING
 	select ARCH_SUPPORTS_PAGE_TABLE_CHECK
 	select ARCH_SUPPORTS_PER_VMA_LOCK
+	select ARCH_SUPPORTS_RT
 	select ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
 	select ARCH_WANT_COMPAT_IPC_PARSE_VERSION if COMPAT
 	select ARCH_WANT_DEFAULT_BPF_JIT

arch/riscv/Kconfig

@@ -65,6 +65,7 @@ config RISCV
 	select ARCH_SUPPORTS_LTO_CLANG_THIN if LLD_VERSION >= 140000
 	select ARCH_SUPPORTS_PAGE_TABLE_CHECK if MMU
 	select ARCH_SUPPORTS_PER_VMA_LOCK if MMU
+	select ARCH_SUPPORTS_RT
 	select ARCH_SUPPORTS_SHADOW_CALL_STACK if HAVE_SHADOW_CALL_STACK
 	select ARCH_USE_CMPXCHG_LOCKREF if 64BIT
 	select ARCH_USE_MEMTEST

arch/x86/Kconfig

@@ -124,6 +124,7 @@ config X86
 	select ARCH_USES_CFI_TRAPS		if X86_64 && CFI_CLANG
 	select ARCH_SUPPORTS_LTO_CLANG
 	select ARCH_SUPPORTS_LTO_CLANG_THIN
+	select ARCH_SUPPORTS_RT
 	select ARCH_USE_BUILTIN_BSWAP
 	select ARCH_USE_CMPXCHG_LOCKREF		if X86_CMPXCHG64
 	select ARCH_USE_MEMTEST

kernel/reboot.c

@@ -34,7 +34,11 @@ EXPORT_SYMBOL(cad_pid);
 #endif
 enum reboot_mode reboot_mode DEFAULT_REBOOT_MODE;
 EXPORT_SYMBOL_GPL(reboot_mode);
+#if defined(CONFIG_ARM64)
+enum reboot_mode panic_reboot_mode = REBOOT_HARD;
+#else
 enum reboot_mode panic_reboot_mode = REBOOT_UNDEFINED;
+#endif
 
 /*
  * This variable is used privately to keep track of whether or not
@@ -43,7 +47,7 @@ enum reboot_mode panic_reboot_mode = REBOOT_UNDEFINED;
  * suppress DMI scanning for reboot quirks.  Without it, it's
  * impossible to override a faulty reboot quirk without recompiling.
  */
-int reboot_default = 1;
+bool reboot_default = true;
 int reboot_cpu;
 enum reboot_type reboot_type = BOOT_ACPI;
 int reboot_force;
@@ -1016,10 +1020,10 @@ static int __init reboot_setup(char *str)
 
 		/*
 		 * Having anything passed on the command line via
-		 * reboot= will cause us to disable DMI checking
+		 * reboot= will cause us to skip DMI checking
 		 * below.
 		 */
-		reboot_default = 0;
+		reboot_default = false;
 
 		if (!strncmp(str, "panic_", 6)) {
 			mode = &panic_reboot_mode;
@@ -1151,7 +1155,7 @@ static ssize_t mode_store(struct kobject *kobj, struct kobj_attribute *attr,
 	else
 		return -EINVAL;
 
-	reboot_default = 0;
+	reboot_default = false;
 
 	return count;
 }
@@ -1173,7 +1177,7 @@ static ssize_t force_store(struct kobject *kobj, struct kobj_attribute *attr,
 	if (kstrtobool(buf, &res))
 		return -EINVAL;
 
-	reboot_default = 0;
+	reboot_default = false;
 	reboot_force = res;
 
 	return count;
@@ -1230,7 +1234,7 @@ static ssize_t type_store(struct kobject *kobj, struct kobj_attribute *attr,
 	else
 		return -EINVAL;
 
-	reboot_default = 0;
+	reboot_default = false;
 
 	return count;
 }
@@ -1259,7 +1263,7 @@ static ssize_t cpu_store(struct kobject *kobj, struct kobj_attribute *attr,
 	if (cpunum >= num_possible_cpus())
 		return -ERANGE;
 
-	reboot_default = 0;
+	reboot_default = false;
 	reboot_cpu = cpunum;
 
 	return count;