1 files changed, 238 insertions, 53 deletions

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 767971a29c7a..78b4b992e1a3 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -29,6 +29,7 @@
 #include <linux/kernel.h>
 #include <linux/sched.h>
 #include <linux/init.h>
+#include <linux/interrupt.h>
 #include <linux/signal.h>
 #include <linux/completion.h>
 #include <linux/workqueue.h>
@@ -72,8 +73,12 @@ enum worker_pool_flags {
 	 * Note that DISASSOCIATED should be flipped only while holding
 	 * wq_pool_attach_mutex to avoid changing binding state while
 	 * worker_attach_to_pool() is in progress.
+	 *
+	 * As there can only be one concurrent BH execution context per CPU, a
+	 * BH pool is per-CPU and always DISASSOCIATED.
 	 */
-	POOL_MANAGER_ACTIVE	= 1 << 0,	/* being managed */
+	POOL_BH			= 1 << 0,	/* is a BH pool */
+	POOL_MANAGER_ACTIVE	= 1 << 1,	/* being managed */
 	POOL_DISASSOCIATED	= 1 << 2,	/* cpu can't serve workers */
 };
 
@@ -116,6 +121,14 @@ enum wq_internal_consts {
 };
 
 /*
+ * We don't want to trap softirq for too long. See MAX_SOFTIRQ_TIME and
+ * MAX_SOFTIRQ_RESTART in kernel/softirq.c. These are macros because
+ * msecs_to_jiffies() can't be an initializer.
+ */
+#define BH_WORKER_JIFFIES	msecs_to_jiffies(2)
+#define BH_WORKER_RESTARTS	10
+
+/*
  * Structure fields follow one of the following exclusion rules.
  *
  * I: Modifiable by initialization/destruction paths and read-only for
@@ -443,8 +456,13 @@ static bool wq_debug_force_rr_cpu = false;
 #endif
 module_param_named(debug_force_rr_cpu, wq_debug_force_rr_cpu, bool, 0644);
 
+/* the BH worker pools */
+static DEFINE_PER_CPU_SHARED_ALIGNED(struct worker_pool [NR_STD_WORKER_POOLS],
+				     bh_worker_pools);
+
 /* the per-cpu worker pools */
-static DEFINE_PER_CPU_SHARED_ALIGNED(struct worker_pool [NR_STD_WORKER_POOLS], cpu_worker_pools);
+static DEFINE_PER_CPU_SHARED_ALIGNED(struct worker_pool [NR_STD_WORKER_POOLS],
+				     cpu_worker_pools);
 
 static DEFINE_IDR(worker_pool_idr);	/* PR: idr of all pools */
 
@@ -478,6 +496,10 @@ struct workqueue_struct *system_power_efficient_wq __ro_after_init;
 EXPORT_SYMBOL_GPL(system_power_efficient_wq);
 struct workqueue_struct *system_freezable_power_efficient_wq __ro_after_init;
 EXPORT_SYMBOL_GPL(system_freezable_power_efficient_wq);
+struct workqueue_struct *system_bh_wq;
+EXPORT_SYMBOL_GPL(system_bh_wq);
+struct workqueue_struct *system_bh_highpri_wq;
+EXPORT_SYMBOL_GPL(system_bh_highpri_wq);
 
 static int worker_thread(void *__worker);
 static void workqueue_sysfs_unregister(struct workqueue_struct *wq);
@@ -498,6 +520,11 @@ static void show_one_worker_pool(struct worker_pool *pool);
 			 !lockdep_is_held(&wq_pool_mutex),		\
 			 "RCU, wq->mutex or wq_pool_mutex should be held")
 
+#define for_each_bh_worker_pool(pool, cpu)				\
+	for ((pool) = &per_cpu(bh_worker_pools, cpu)[0];		\
+	     (pool) < &per_cpu(bh_worker_pools, cpu)[NR_STD_WORKER_POOLS]; \
+	     (pool)++)
+
 #define for_each_cpu_worker_pool(pool, cpu)				\
 	for ((pool) = &per_cpu(cpu_worker_pools, cpu)[0];		\
 	     (pool) < &per_cpu(cpu_worker_pools, cpu)[NR_STD_WORKER_POOLS]; \
@@ -1186,6 +1213,14 @@ static bool kick_pool(struct worker_pool *pool)
 	if (!need_more_worker(pool) || !worker)
 		return false;
 
+	if (pool->flags & POOL_BH) {
+		if (pool->attrs->nice == HIGHPRI_NICE_LEVEL)
+			raise_softirq_irqoff(HI_SOFTIRQ);
+		else
+			raise_softirq_irqoff(TASKLET_SOFTIRQ);
+		return true;
+	}
+
 	p = worker->task;
 
 #ifdef CONFIG_SMP
@@ -1668,7 +1703,7 @@ static bool pwq_tryinc_nr_active(struct pool_workqueue *pwq, bool fill)
 	lockdep_assert_held(&pool->lock);
 
 	if (!nna) {
-		/* per-cpu workqueue, pwq->nr_active is sufficient */
+		/* BH or per-cpu workqueue, pwq->nr_active is sufficient */
 		obtained = pwq->nr_active < READ_ONCE(wq->max_active);
 		goto out;
 	}
@@ -2523,19 +2558,21 @@ static cpumask_t *pool_allowed_cpus(struct worker_pool *pool)
  * cpu-[un]hotplugs.
  */
 static void worker_attach_to_pool(struct worker *worker,
-				   struct worker_pool *pool)
+				  struct worker_pool *pool)
 {
 	mutex_lock(&wq_pool_attach_mutex);
 
 	/*
-	 * The wq_pool_attach_mutex ensures %POOL_DISASSOCIATED remains
-	 * stable across this function.  See the comments above the flag
-	 * definition for details.
+	 * The wq_pool_attach_mutex ensures %POOL_DISASSOCIATED remains stable
+	 * across this function. See the comments above the flag definition for
+	 * details. BH workers are, while per-CPU, always DISASSOCIATED.
 	 */
-	if (pool->flags & POOL_DISASSOCIATED)
+	if (pool->flags & POOL_DISASSOCIATED) {
 		worker->flags |= WORKER_UNBOUND;
-	else
+	} else {
+		WARN_ON_ONCE(pool->flags & POOL_BH);
 		kthread_set_per_cpu(worker->task, pool->cpu);
+	}
 
 	if (worker->rescue_wq)
 		set_cpus_allowed_ptr(worker->task, pool_allowed_cpus(pool));
@@ -2559,6 +2596,9 @@ static void worker_detach_from_pool(struct worker *worker)
 	struct worker_pool *pool = worker->pool;
 	struct completion *detach_completion = NULL;
 
+	/* there is one permanent BH worker per CPU which should never detach */
+	WARN_ON_ONCE(pool->flags & POOL_BH);
+
 	mutex_lock(&wq_pool_attach_mutex);
 
 	kthread_set_per_cpu(worker->task, -1);
@@ -2610,27 +2650,29 @@ static struct worker *create_worker(struct worker_pool *pool)
 
 	worker->id = id;
 
-	if (pool->cpu >= 0)
-		snprintf(id_buf, sizeof(id_buf), "%d:%d%s", pool->cpu, id,
-			 pool->attrs->nice < 0  ? "H" : "");
-	else
-		snprintf(id_buf, sizeof(id_buf), "u%d:%d", pool->id, id);
-
-	worker->task = kthread_create_on_node(worker_thread, worker, pool->node,
-					      "kworker/%s", id_buf);
-	if (IS_ERR(worker->task)) {
-		if (PTR_ERR(worker->task) == -EINTR) {
-			pr_err("workqueue: Interrupted when creating a worker thread \"kworker/%s\"\n",
-			       id_buf);
-		} else {
-			pr_err_once("workqueue: Failed to create a worker thread: %pe",
-				    worker->task);
+	if (!(pool->flags & POOL_BH)) {
+		if (pool->cpu >= 0)
+			snprintf(id_buf, sizeof(id_buf), "%d:%d%s", pool->cpu, id,
+				 pool->attrs->nice < 0  ? "H" : "");
+		else
+			snprintf(id_buf, sizeof(id_buf), "u%d:%d", pool->id, id);
+
+		worker->task = kthread_create_on_node(worker_thread, worker,
+					pool->node, "kworker/%s", id_buf);
+		if (IS_ERR(worker->task)) {
+			if (PTR_ERR(worker->task) == -EINTR) {
+				pr_err("workqueue: Interrupted when creating a worker thread \"kworker/%s\"\n",
+				       id_buf);
+			} else {
+				pr_err_once("workqueue: Failed to create a worker thread: %pe",
+					    worker->task);
+			}
+			goto fail;
 		}
-		goto fail;
-	}
 
-	set_user_nice(worker->task, pool->attrs->nice);
-	kthread_bind_mask(worker->task, pool_allowed_cpus(pool));
+		set_user_nice(worker->task, pool->attrs->nice);
+		kthread_bind_mask(worker->task, pool_allowed_cpus(pool));
+	}
 
 	/* successful, attach the worker to the pool */
 	worker_attach_to_pool(worker, pool);
@@ -2646,7 +2688,8 @@ static struct worker *create_worker(struct worker_pool *pool)
 	 * check if not woken up soon. As kick_pool() is noop if @pool is empty,
 	 * wake it up explicitly.
 	 */
-	wake_up_process(worker->task);
+	if (worker->task)
+		wake_up_process(worker->task);
 
 	raw_spin_unlock_irq(&pool->lock);
 
@@ -2988,7 +3031,8 @@ __acquires(&pool->lock)
 	worker->current_work = work;
 	worker->current_func = work->func;
 	worker->current_pwq = pwq;
-	worker->current_at = worker->task->se.sum_exec_runtime;
+	if (worker->task)
+		worker->current_at = worker->task->se.sum_exec_runtime;
 	work_data = *work_data_bits(work);
 	worker->current_color = get_work_color(work_data);
 
@@ -3086,7 +3130,8 @@ __acquires(&pool->lock)
 	 * stop_machine. At the same time, report a quiescent RCU state so
 	 * the same condition doesn't freeze RCU.
 	 */
-	cond_resched();
+	if (worker->task)
+		cond_resched();
 
 	raw_spin_lock_irq(&pool->lock);
 
@@ -3369,6 +3414,61 @@ repeat:
 	goto repeat;
 }
 
+static void bh_worker(struct worker *worker)
+{
+	struct worker_pool *pool = worker->pool;
+	int nr_restarts = BH_WORKER_RESTARTS;
+	unsigned long end = jiffies + BH_WORKER_JIFFIES;
+
+	raw_spin_lock_irq(&pool->lock);
+	worker_leave_idle(worker);
+
+	/*
+	 * This function follows the structure of worker_thread(). See there for
+	 * explanations on each step.
+	 */
+	if (!need_more_worker(pool))
+		goto done;
+
+	WARN_ON_ONCE(!list_empty(&worker->scheduled));
+	worker_clr_flags(worker, WORKER_PREP | WORKER_REBOUND);
+
+	do {
+		struct work_struct *work =
+			list_first_entry(&pool->worklist,
+					 struct work_struct, entry);
+
+		if (assign_work(work, worker, NULL))
+			process_scheduled_works(worker);
+	} while (keep_working(pool) &&
+		 --nr_restarts && time_before(jiffies, end));
+
+	worker_set_flags(worker, WORKER_PREP);
+done:
+	worker_enter_idle(worker);
+	kick_pool(pool);
+	raw_spin_unlock_irq(&pool->lock);
+}
+
+/*
+ * TODO: Convert all tasklet users to workqueue and use softirq directly.
+ *
+ * This is currently called from tasklet[_hi]action() and thus is also called
+ * whenever there are tasklets to run. Let's do an early exit if there's nothing
+ * queued. Once conversion from tasklet is complete, the need_more_worker() test
+ * can be dropped.
+ *
+ * After full conversion, we'll add worker->softirq_action, directly use the
+ * softirq action and obtain the worker pointer from the softirq_action pointer.
+ */
+void workqueue_softirq_action(bool highpri)
+{
+	struct worker_pool *pool =
+		&per_cpu(bh_worker_pools, smp_processor_id())[highpri];
+	if (need_more_worker(pool))
+		bh_worker(list_first_entry(&pool->workers, struct worker, node));
+}
+
 /**
  * check_flush_dependency - check for flush dependency sanity
  * @target_wq: workqueue being flushed
@@ -3441,6 +3541,7 @@ static void insert_wq_barrier(struct pool_workqueue *pwq,
 			      struct wq_barrier *barr,
 			      struct work_struct *target, struct worker *worker)
 {
+	static __maybe_unused struct lock_class_key bh_key, thr_key;
 	unsigned int work_flags = 0;
 	unsigned int work_color;
 	struct list_head *head;
@@ -3450,8 +3551,13 @@ static void insert_wq_barrier(struct pool_workqueue *pwq,
 	 * as we know for sure that this will not trigger any of the
 	 * checks and call back into the fixup functions where we
 	 * might deadlock.
+	 *
+	 * BH and threaded workqueues need separate lockdep keys to avoid
+	 * spuriously triggering "inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W}
+	 * usage".
 	 */
-	INIT_WORK_ONSTACK(&barr->work, wq_barrier_func);
+	INIT_WORK_ONSTACK_KEY(&barr->work, wq_barrier_func,
+			      (pwq->wq->flags & WQ_BH) ? &bh_key : &thr_key);
 	__set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(&barr->work));
 
 	init_completion_map(&barr->done, &target->lockdep_map);
@@ -3557,15 +3663,31 @@ static bool flush_workqueue_prep_pwqs(struct workqueue_struct *wq,
 
 static void touch_wq_lockdep_map(struct workqueue_struct *wq)
 {
+#ifdef CONFIG_LOCKDEP
+	if (wq->flags & WQ_BH)
+		local_bh_disable();
+
 	lock_map_acquire(&wq->lockdep_map);
 	lock_map_release(&wq->lockdep_map);
+
+	if (wq->flags & WQ_BH)
+		local_bh_enable();
+#endif
 }
 
 static void touch_work_lockdep_map(struct work_struct *work,
 				   struct workqueue_struct *wq)
 {
+#ifdef CONFIG_LOCKDEP
+	if (wq->flags & WQ_BH)
+		local_bh_disable();
+
 	lock_map_acquire(&work->lockdep_map);
 	lock_map_release(&work->lockdep_map);
+
+	if (wq->flags & WQ_BH)
+		local_bh_enable();
+#endif
 }
 
 /**
@@ -5019,10 +5141,17 @@ static int alloc_and_link_pwqs(struct workqueue_struct *wq)
 
 	if (!(wq->flags & WQ_UNBOUND)) {
 		for_each_possible_cpu(cpu) {
-			struct pool_workqueue **pwq_p =
-				per_cpu_ptr(wq->cpu_pwq, cpu);
-			struct worker_pool *pool =
-				&(per_cpu_ptr(cpu_worker_pools, cpu)[highpri]);
+			struct pool_workqueue **pwq_p;
+			struct worker_pool __percpu *pools;
+			struct worker_pool *pool;
+
+			if (wq->flags & WQ_BH)
+				pools = bh_worker_pools;
+			else
+				pools = cpu_worker_pools;
+
+			pool = &(per_cpu_ptr(pools, cpu)[highpri]);
+			pwq_p = per_cpu_ptr(wq->cpu_pwq, cpu);
 
 			*pwq_p = kmem_cache_alloc_node(pwq_cache, GFP_KERNEL,
 						       pool->node);
@@ -5197,6 +5326,13 @@ struct workqueue_struct *alloc_workqueue(const char *fmt,
 	size_t wq_size;
 	int name_len;
 
+	if (flags & WQ_BH) {
+		if (WARN_ON_ONCE(flags & ~__WQ_BH_ALLOWS))
+			return NULL;
+		if (WARN_ON_ONCE(max_active))
+			return NULL;
+	}
+
 	/*
 	 * Unbound && max_active == 1 used to imply ordered, which is no longer
 	 * the case on many machines due to per-pod pools. While
@@ -5234,8 +5370,16 @@ struct workqueue_struct *alloc_workqueue(const char *fmt,
 		pr_warn_once("workqueue: name exceeds WQ_NAME_LEN. Truncating to: %s\n",
 			     wq->name);
 
-	max_active = max_active ?: WQ_DFL_ACTIVE;
-	max_active = wq_clamp_max_active(max_active, flags, wq->name);
+	if (flags & WQ_BH) {
+		/*
+		 * BH workqueues always share a single execution context per CPU
+		 * and don't impose any max_active limit.
+		 */
+		max_active = INT_MAX;
+	} else {
+		max_active = max_active ?: WQ_DFL_ACTIVE;
+		max_active = wq_clamp_max_active(max_active, flags, wq->name);
+	}
 
 	/* init wq */
 	wq->flags = flags;
@@ -5416,6 +5560,9 @@ EXPORT_SYMBOL_GPL(destroy_workqueue);
  */
 void workqueue_set_max_active(struct workqueue_struct *wq, int max_active)
 {
+	/* max_active doesn't mean anything for BH workqueues */
+	if (WARN_ON(wq->flags & WQ_BH))
+		return;
 	/* disallow meddling with max_active for ordered workqueues */
 	if (WARN_ON(wq->flags & __WQ_ORDERED_EXPLICIT))
 		return;
@@ -5617,7 +5764,24 @@ static void pr_cont_pool_info(struct worker_pool *pool)
 	pr_cont(" cpus=%*pbl", nr_cpumask_bits, pool->attrs->cpumask);
 	if (pool->node != NUMA_NO_NODE)
 		pr_cont(" node=%d", pool->node);
-	pr_cont(" flags=0x%x nice=%d", pool->flags, pool->attrs->nice);
+	pr_cont(" flags=0x%x", pool->flags);
+	if (pool->flags & POOL_BH)
+		pr_cont(" bh%s",
+			pool->attrs->nice == HIGHPRI_NICE_LEVEL ? "-hi" : "");
+	else
+		pr_cont(" nice=%d", pool->attrs->nice);
+}
+
+static void pr_cont_worker_id(struct worker *worker)
+{
+	struct worker_pool *pool = worker->pool;
+
+	if (pool->flags & WQ_BH)
+		pr_cont("bh%s",
+			pool->attrs->nice == HIGHPRI_NICE_LEVEL ? "-hi" : "");
+	else
+		pr_cont("%d%s", task_pid_nr(worker->task),
+			worker->rescue_wq ? "(RESCUER)" : "");
 }
 
 struct pr_cont_work_struct {
@@ -5694,10 +5858,9 @@ static void show_pwq(struct pool_workqueue *pwq)
 			if (worker->current_pwq != pwq)
 				continue;
 
-			pr_cont("%s %d%s:%ps", comma ? "," : "",
-				task_pid_nr(worker->task),
-				worker->rescue_wq ? "(RESCUER)" : "",
-				worker->current_func);
+			pr_cont(" %s", comma ? "," : "");
+			pr_cont_worker_id(worker);
+			pr_cont(":%ps", worker->current_func);
 			list_for_each_entry(work, &worker->scheduled, entry)
 				pr_cont_work(false, work, &pcws);
 			pr_cont_work_flush(comma, (work_func_t)-1L, &pcws);
@@ -5816,8 +5979,8 @@ static void show_one_worker_pool(struct worker_pool *pool)
 		pr_cont(" manager: %d",
 			task_pid_nr(pool->manager->task));
 	list_for_each_entry(worker, &pool->idle_list, entry) {
-		pr_cont(" %s%d", first ? "idle: " : "",
-			task_pid_nr(worker->task));
+		pr_cont(" %s", first ? "idle: " : "");
+		pr_cont_worker_id(worker);
 		first = false;
 	}
 	pr_cont("\n");
@@ -6090,13 +6253,15 @@ int workqueue_online_cpu(unsigned int cpu)
 	mutex_lock(&wq_pool_mutex);
 
 	for_each_pool(pool, pi) {
-		mutex_lock(&wq_pool_attach_mutex);
+		/* BH pools aren't affected by hotplug */
+		if (pool->flags & POOL_BH)
+			continue;
 
+		mutex_lock(&wq_pool_attach_mutex);
 		if (pool->cpu == cpu)
 			rebind_workers(pool);
 		else if (pool->cpu < 0)
 			restore_unbound_workers_cpumask(pool, cpu);
-
 		mutex_unlock(&wq_pool_attach_mutex);
 	}
 
@@ -7053,7 +7218,7 @@ static void wq_watchdog_timer_fn(struct timer_list *unused)
 		/* did we stall? */
 		if (time_after(now, ts + thresh)) {
 			lockup_detected = true;
-			if (pool->cpu >= 0) {
+			if (pool->cpu >= 0 && !(pool->flags & POOL_BH)) {
 				pool->cpu_stall = true;
 				cpu_pool_stall = true;
 			}
@@ -7218,11 +7383,17 @@ void __init workqueue_init_early(void)
 	pt->pod_node[0] = NUMA_NO_NODE;
 	pt->cpu_pod[0] = 0;
 
-	/* initialize CPU pools */
+	/* initialize BH and CPU pools */
 	for_each_possible_cpu(cpu) {
 		struct worker_pool *pool;
 
 		i = 0;
+		for_each_bh_worker_pool(pool, cpu) {
+			init_cpu_worker_pool(pool, cpu, std_nice[i++]);
+			pool->flags |= POOL_BH;
+		}
+
+		i = 0;
 		for_each_cpu_worker_pool(pool, cpu)
 			init_cpu_worker_pool(pool, cpu, std_nice[i++]);
 	}
@@ -7257,10 +7428,14 @@ void __init workqueue_init_early(void)
 	system_freezable_power_efficient_wq = alloc_workqueue("events_freezable_pwr_efficient",
 					      WQ_FREEZABLE | WQ_POWER_EFFICIENT,
 					      0);
+	system_bh_wq = alloc_workqueue("events_bh", WQ_BH, 0);
+	system_bh_highpri_wq = alloc_workqueue("events_bh_highpri",
+					       WQ_BH | WQ_HIGHPRI, 0);
 	BUG_ON(!system_wq || !system_highpri_wq || !system_long_wq ||
 	       !system_unbound_wq || !system_freezable_wq ||
 	       !system_power_efficient_wq ||
-	       !system_freezable_power_efficient_wq);
+	       !system_freezable_power_efficient_wq ||
+	       !system_bh_wq || !system_bh_highpri_wq);
 }
 
 static void __init wq_cpu_intensive_thresh_init(void)
@@ -7326,9 +7501,10 @@ void __init workqueue_init(void)
 	 * up. Also, create a rescuer for workqueues that requested it.
 	 */
 	for_each_possible_cpu(cpu) {
-		for_each_cpu_worker_pool(pool, cpu) {
+		for_each_bh_worker_pool(pool, cpu)
+			pool->node = cpu_to_node(cpu);
+		for_each_cpu_worker_pool(pool, cpu)
 			pool->node = cpu_to_node(cpu);
-		}
 	}
 
 	list_for_each_entry(wq, &workqueues, list) {
@@ -7339,7 +7515,16 @@ void __init workqueue_init(void)
 
 	mutex_unlock(&wq_pool_mutex);
 
-	/* create the initial workers */
+	/*
+	 * Create the initial workers. A BH pool has one pseudo worker that
+	 * represents the shared BH execution context and thus doesn't get
+	 * affected by hotplug events. Create the BH pseudo workers for all
+	 * possible CPUs here.
+	 */
+	for_each_possible_cpu(cpu)
+		for_each_bh_worker_pool(pool, cpu)
+			BUG_ON(!create_worker(pool));
+
 	for_each_online_cpu(cpu) {
 		for_each_cpu_worker_pool(pool, cpu) {
 			pool->flags &= ~POOL_DISASSOCIATED;