Merge tag 'kthread-for-7.0' of git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks

Pull kthread updates from Frederic Weisbecker:
 "The kthread code provides an infrastructure which manages the
  preferred affinity of unbound kthreads (node or custom cpumask)
  against housekeeping (CPU isolation) constraints and CPU hotplug
  events.

  One crucial missing piece is the handling of cpuset: when an isolated
  partition is created, deleted, or its CPUs updated, all the unbound
  kthreads in the top cpuset become indifferently affine to _all_ the
  non-isolated CPUs, possibly breaking their preferred affinity along
  the way.

  Solve this with performing the kthreads affinity update from cpuset to
  the kthreads consolidated relevant code instead so that preferred
  affinities are honoured and applied against the updated cpuset
  isolated partitions.

  The dispatch of the new isolated cpumasks to timers, workqueues and
  kthreads is performed by housekeeping, as per the nice Tejun's
  suggestion.

  As a welcome side effect, HK_TYPE_DOMAIN then integrates both the set
  from boot defined domain isolation (through isolcpus=) and cpuset
  isolated partitions. Housekeeping cpumasks are now modifiable with a
  specific RCU based synchronization. A big step toward making
  nohz_full= also mutable through cpuset in the future"

* tag 'kthread-for-7.0' of git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks: (33 commits)
  doc: Add housekeeping documentation
  kthread: Document kthread_affine_preferred()
  kthread: Comment on the purpose and placement of kthread_affine_node() call
  kthread: Honour kthreads preferred affinity after cpuset changes
  sched/arm64: Move fallback task cpumask to HK_TYPE_DOMAIN
  sched: Switch the fallback task allowed cpumask to HK_TYPE_DOMAIN
  kthread: Rely on HK_TYPE_DOMAIN for preferred affinity management
  kthread: Include kthreadd to the managed affinity list
  kthread: Include unbound kthreads in the managed affinity list
  kthread: Refine naming of affinity related fields
  PCI: Remove superfluous HK_TYPE_WQ check
  sched/isolation: Remove HK_TYPE_TICK test from cpu_is_isolated()
  cpuset: Remove cpuset_cpu_is_isolated()
  timers/migration: Remove superfluous cpuset isolation test
  cpuset: Propagate cpuset isolation update to timers through housekeeping
  cpuset: Propagate cpuset isolation update to workqueue through housekeeping
  PCI: Flush PCI probe workqueue on cpuset isolated partition change
  sched/isolation: Flush vmstat workqueues on cpuset isolated partition change
  sched/isolation: Flush memcg workqueues on cpuset isolated partition change
  cpuset: Update HK_TYPE_DOMAIN cpumask from cpuset
  ...

Author: torvalds

Documentation/arch/arm64/asymmetric-32bit.rst

@@ -154,10 +154,14 @@ mode will return to host userspace with an ``exit_reason`` of
 ``KVM_EXIT_FAIL_ENTRY`` and will remain non-runnable until successfully
 re-initialised by a subsequent ``KVM_ARM_VCPU_INIT`` operation.
 
-NOHZ FULL
----------
+SCHEDULER DOMAIN ISOLATION
+--------------------------
 
-To avoid perturbing an adaptive-ticks CPU (specified using
-``nohz_full=``) when a 32-bit task is forcefully migrated, these CPUs
+To avoid perturbing a boot-defined domain isolated CPU (specified using
+``isolcpus=[domain]``) when a 32-bit task is forcefully migrated, these CPUs
 are treated as 64-bit-only when support for asymmetric 32-bit systems
 is enabled.
+
+However as opposed to boot-defined domain isolation, runtime-defined domain
+isolation using cpuset isolated partition is not advised on asymmetric
+32-bit systems and will result in undefined behaviour.

Documentation/core-api/housekeeping.rst

@@ -0,0 +1,111 @@
+======================================
+Housekeeping
+======================================
+
+
+CPU Isolation moves away kernel work that may otherwise run on any CPU.
+The purpose of its related features is to reduce the OS jitter that some
+extreme workloads can't stand, such as in some DPDK usecases.
+
+The kernel work moved away by CPU isolation is commonly described as
+"housekeeping" because it includes ground work that performs cleanups,
+statistics maintainance and actions relying on them, memory release,
+various deferrals etc...
+
+Sometimes housekeeping is just some unbound work (unbound workqueues,
+unbound timers, ...) that gets easily assigned to non-isolated CPUs.
+But sometimes housekeeping is tied to a specific CPU and requires
+elaborated tricks to be offloaded to non-isolated CPUs (RCU_NOCB, remote
+scheduler tick, etc...).
+
+Thus, a housekeeping CPU can be considered as the reverse of an isolated
+CPU. It is simply a CPU that can execute housekeeping work. There must
+always be at least one online housekeeping CPU at any time. The CPUs that
+are not	isolated are automatically assigned as housekeeping.
+
+Housekeeping is currently divided in four features described
+by the ``enum hk_type type``:
+
+1.	HK_TYPE_DOMAIN matches the work moved away by scheduler domain
+	isolation performed through ``isolcpus=domain`` boot parameter or
+	isolated cpuset partitions in cgroup v2. This includes scheduler
+	load balancing, unbound workqueues and timers.
+
+2.	HK_TYPE_KERNEL_NOISE matches the work moved away by tick isolation
+	performed through ``nohz_full=`` or ``isolcpus=nohz`` boot
+	parameters. This includes remote scheduler tick, vmstat and lockup
+	watchdog.
+
+3.	HK_TYPE_MANAGED_IRQ matches the IRQ handlers moved away by managed
+	IRQ isolation performed through ``isolcpus=managed_irq``.
+
+4.	HK_TYPE_DOMAIN_BOOT matches the work moved away by scheduler domain
+	isolation performed through ``isolcpus=domain`` only. It is similar
+	to HK_TYPE_DOMAIN except it ignores the isolation performed by
+	cpusets.
+
+
+Housekeeping cpumasks
+=================================
+
+Housekeeping cpumasks include the CPUs that can execute the work moved
+away by the matching isolation feature. These cpumasks are returned by
+the following function::
+
+	const struct cpumask *housekeeping_cpumask(enum hk_type type)
+
+By default, if neither ``nohz_full=``, nor ``isolcpus``, nor cpuset's
+isolated partitions are used, which covers most usecases, this function
+returns the cpu_possible_mask.
+
+Otherwise the function returns the cpumask complement of the isolation
+feature. For example:
+
+With isolcpus=domain,7 the following will return a mask with all possible
+CPUs except 7::
+
+	housekeeping_cpumask(HK_TYPE_DOMAIN)
+
+Similarly with nohz_full=5,6 the following will return a mask with all
+possible CPUs except 5,6::
+
+	housekeeping_cpumask(HK_TYPE_KERNEL_NOISE)
+
+
+Synchronization against cpusets
+=================================
+
+Cpuset can modify the HK_TYPE_DOMAIN housekeeping cpumask while creating,
+modifying or deleting an isolated partition.
+
+The users of HK_TYPE_DOMAIN cpumask must then make sure to synchronize
+properly against cpuset in order to make sure that:
+
+1.	The cpumask snapshot stays coherent.
+
+2.	No housekeeping work is queued on a newly made isolated CPU.
+
+3.	Pending housekeeping work that was queued to a non isolated
+	CPU which just turned isolated through cpuset must be flushed
+	before the related created/modified isolated partition is made
+	available to userspace.
+
+This synchronization is maintained by an RCU based scheme. The cpuset update
+side waits for an RCU grace period after updating the HK_TYPE_DOMAIN
+cpumask and before flushing pending works. On the read side, care must be
+taken to gather the housekeeping target election and the work enqueue within
+the same RCU read side critical section.
+
+A typical layout example would look like this on the update side
+(``housekeeping_update()``)::
+
+	rcu_assign_pointer(housekeeping_cpumasks[type], trial);
+	synchronize_rcu();
+	flush_workqueue(example_workqueue);
+
+And then on the read side::
+
+	rcu_read_lock();
+	cpu = housekeeping_any_cpu(HK_TYPE_DOMAIN);
+	queue_work_on(cpu, example_workqueue, work);
+	rcu_read_unlock();

Documentation/core-api/index.rst

@@ -25,6 +25,7 @@ it.
    symbol-namespaces
    asm-annotations
    real-time/index
+   housekeeping.rst
 
 Data structures and low-level utilities
 =======================================

arch/arm64/kernel/cpufeature.c

@@ -1669,7 +1669,7 @@ const struct cpumask *system_32bit_el0_cpumask(void)
 
 const struct cpumask *task_cpu_fallback_mask(struct task_struct *p)
 {
-	return __task_cpu_possible_mask(p, housekeeping_cpumask(HK_TYPE_TICK));
+	return __task_cpu_possible_mask(p, housekeeping_cpumask(HK_TYPE_DOMAIN));
 }
 
 static int __init parse_32bit_el0_param(char *str)
@@ -3987,8 +3987,8 @@ static int enable_mismatched_32bit_el0(unsigned int cpu)
 	bool cpu_32bit = false;
 
 	if (id_aa64pfr0_32bit_el0(info->reg_id_aa64pfr0)) {
-		if (!housekeeping_cpu(cpu, HK_TYPE_TICK))
-			pr_info("Treating adaptive-ticks CPU %u as 64-bit only\n", cpu);
+		if (!housekeeping_cpu(cpu, HK_TYPE_DOMAIN))
+			pr_info("Treating domain isolated CPU %u as 64-bit only\n", cpu);
 		else
 			cpu_32bit = true;
 	}

block/blk-mq.c

@@ -4270,12 +4270,16 @@ static void blk_mq_map_swqueue(struct request_queue *q)
 
 		/*
 		 * Rule out isolated CPUs from hctx->cpumask to avoid
-		 * running block kworker on isolated CPUs
+		 * running block kworker on isolated CPUs.
+		 * FIXME: cpuset should propagate further changes to isolated CPUs
+		 * here.
 		 */
+		rcu_read_lock();
 		for_each_cpu(cpu, hctx->cpumask) {
 			if (cpu_is_isolated(cpu))
 				cpumask_clear_cpu(cpu, hctx->cpumask);
 		}
+		rcu_read_unlock();
 
 		/*
 		 * Initialize batch roundrobin counts

drivers/base/cpu.c

@@ -291,7 +291,7 @@ static ssize_t print_cpus_isolated(struct device *dev,
 		return -ENOMEM;
 
 	cpumask_andnot(isolated, cpu_possible_mask,
-		       housekeeping_cpumask(HK_TYPE_DOMAIN));
+		       housekeeping_cpumask(HK_TYPE_DOMAIN_BOOT));
 	len = sysfs_emit(buf, "%*pbl\n", cpumask_pr_args(isolated));
 
 	free_cpumask_var(isolated);

drivers/pci/pci-driver.c

@@ -302,9 +302,8 @@ struct drv_dev_and_id {
 	const struct pci_device_id *id;
 };
 
-static long local_pci_probe(void *_ddi)
+static int local_pci_probe(struct drv_dev_and_id *ddi)
 {
-	struct drv_dev_and_id *ddi = _ddi;
 	struct pci_dev *pci_dev = ddi->dev;
 	struct pci_driver *pci_drv = ddi->drv;
 	struct device *dev = &pci_dev->dev;
@@ -338,6 +337,21 @@ static long local_pci_probe(void *_ddi)
 	return 0;
 }
 
+static struct workqueue_struct *pci_probe_wq;
+
+struct pci_probe_arg {
+	struct drv_dev_and_id *ddi;
+	struct work_struct work;
+	int ret;
+};
+
+static void local_pci_probe_callback(struct work_struct *work)
+{
+	struct pci_probe_arg *arg = container_of(work, struct pci_probe_arg, work);
+
+	arg->ret = local_pci_probe(arg->ddi);
+}
+
 static bool pci_physfn_is_probed(struct pci_dev *dev)
 {
 #ifdef CONFIG_PCI_IOV
@@ -362,40 +376,55 @@ static int pci_call_probe(struct pci_driver *drv, struct pci_dev *dev,
 	dev->is_probed = 1;
 
 	cpu_hotplug_disable();
-
 	/*
 	 * Prevent nesting work_on_cpu() for the case where a Virtual Function
 	 * device is probed from work_on_cpu() of the Physical device.
 	 */
 	if (node < 0 || node >= MAX_NUMNODES || !node_online(node) ||
 	    pci_physfn_is_probed(dev)) {
-		cpu = nr_cpu_ids;
+		error = local_pci_probe(&ddi);
 	} else {
-		cpumask_var_t wq_domain_mask;
+		struct pci_probe_arg arg = { .ddi = &ddi };
 
-		if (!zalloc_cpumask_var(&wq_domain_mask, GFP_KERNEL)) {
-			error = -ENOMEM;
-			goto out;
+		INIT_WORK_ONSTACK(&arg.work, local_pci_probe_callback);
+		/*
+		 * The target election and the enqueue of the work must be within
+		 * the same RCU read side section so that when the workqueue pool
+		 * is flushed after a housekeeping cpumask update, further readers
+		 * are guaranteed to queue the probing work to the appropriate
+		 * targets.
+		 */
+		rcu_read_lock();
+		cpu = cpumask_any_and(cpumask_of_node(node),
+				      housekeeping_cpumask(HK_TYPE_DOMAIN));
+
+		if (cpu < nr_cpu_ids) {
+			struct workqueue_struct *wq = pci_probe_wq;
+
+			if (WARN_ON_ONCE(!wq))
+				wq = system_percpu_wq;
+			queue_work_on(cpu, wq, &arg.work);
+			rcu_read_unlock();
+			flush_work(&arg.work);
+			error = arg.ret;
+		} else {
+			rcu_read_unlock();
+			error = local_pci_probe(&ddi);
 		}
-		cpumask_and(wq_domain_mask,
-			    housekeeping_cpumask(HK_TYPE_WQ),
-			    housekeeping_cpumask(HK_TYPE_DOMAIN));
 
-		cpu = cpumask_any_and(cpumask_of_node(node),
-				      wq_domain_mask);
-		free_cpumask_var(wq_domain_mask);
+		destroy_work_on_stack(&arg.work);
 	}
 
-	if (cpu < nr_cpu_ids)
-		error = work_on_cpu(cpu, local_pci_probe, &ddi);
-	else
-		error = local_pci_probe(&ddi);
-out:
 	dev->is_probed = 0;
 	cpu_hotplug_enable();
 	return error;
 }
 
+void pci_probe_flush_workqueue(void)
+{
+	flush_workqueue(pci_probe_wq);
+}
+
 /**
  * __pci_device_probe - check if a driver wants to claim a specific PCI device
  * @drv: driver to call to check if it wants the PCI device
@@ -1733,6 +1762,10 @@ static int __init pci_driver_init(void)
 {
 	int ret;
 
+	pci_probe_wq = alloc_workqueue("sync_wq", WQ_PERCPU, 0);
+	if (!pci_probe_wq)
+		return -ENOMEM;
+
 	ret = bus_register(&pci_bus_type);
 	if (ret)
 		return ret;

include/linux/cpuhplock.h

@@ -13,6 +13,7 @@
 struct device;
 
 extern int lockdep_is_cpus_held(void);
+extern int lockdep_is_cpus_write_held(void);
 
 #ifdef CONFIG_HOTPLUG_CPU
 void cpus_write_lock(void);

include/linux/cpuset.h

@@ -18,6 +18,8 @@
 #include <linux/mmu_context.h>
 #include <linux/jump_label.h>
 
+extern bool lockdep_is_cpuset_held(void);
+
 #ifdef CONFIG_CPUSETS
 
 /*
@@ -77,7 +79,6 @@ extern void cpuset_unlock(void);
 extern void cpuset_cpus_allowed_locked(struct task_struct *p, struct cpumask *mask);
 extern void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask);
 extern bool cpuset_cpus_allowed_fallback(struct task_struct *p);
-extern bool cpuset_cpu_is_isolated(int cpu);
 extern nodemask_t cpuset_mems_allowed(struct task_struct *p);
 #define cpuset_current_mems_allowed (current->mems_allowed)
 void cpuset_init_current_mems_allowed(void);
@@ -213,11 +214,6 @@ static inline bool cpuset_cpus_allowed_fallback(struct task_struct *p)
 	return false;
 }
 
-static inline bool cpuset_cpu_is_isolated(int cpu)
-{
-	return false;
-}
-
 static inline nodemask_t cpuset_mems_allowed(struct task_struct *p)
 {
 	return node_possible_map;

include/linux/kthread.h

@@ -100,6 +100,7 @@ void kthread_unpark(struct task_struct *k);
 void kthread_parkme(void);
 void kthread_exit(long result) __noreturn;
 void kthread_complete_and_exit(struct completion *, long) __noreturn;
+int kthreads_update_housekeeping(void);
 
 int kthreadd(void *unused);
 extern struct task_struct *kthreadd_task;