1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 * Pressure stall information for CPU, memory and IO
   4 *
   5 * Copyright (c) 2018 Facebook, Inc.
   6 * Author: Johannes Weiner <hannes@cmpxchg.org>
   7 *
   8 * Polling support by Suren Baghdasaryan <surenb@google.com>
   9 * Copyright (c) 2018 Google, Inc.
  10 *
  11 * When CPU, memory and IO are contended, tasks experience delays that
  12 * reduce throughput and introduce latencies into the workload. Memory
  13 * and IO contention, in addition, can cause a full loss of forward
  14 * progress in which the CPU goes idle.
  15 *
  16 * This code aggregates individual task delays into resource pressure
  17 * metrics that indicate problems with both workload health and
  18 * resource utilization.
  19 *
  20 *			Model
  21 *
  22 * The time in which a task can execute on a CPU is our baseline for
  23 * productivity. Pressure expresses the amount of time in which this
  24 * potential cannot be realized due to resource contention.
  25 *
  26 * This concept of productivity has two components: the workload and
  27 * the CPU. To measure the impact of pressure on both, we define two
  28 * contention states for a resource: SOME and FULL.
  29 *
  30 * In the SOME state of a given resource, one or more tasks are
  31 * delayed on that resource. This affects the workload's ability to
  32 * perform work, but the CPU may still be executing other tasks.
  33 *
  34 * In the FULL state of a given resource, all non-idle tasks are
  35 * delayed on that resource such that nobody is advancing and the CPU
  36 * goes idle. This leaves both workload and CPU unproductive.
  37 *
  38 *	SOME = nr_delayed_tasks != 0
  39 *	FULL = nr_delayed_tasks != 0 && nr_productive_tasks == 0
  40 *
  41 * What it means for a task to be productive is defined differently
  42 * for each resource. For IO, productive means a running task. For
  43 * memory, productive means a running task that isn't a reclaimer. For
  44 * CPU, productive means an on-CPU task.
  45 *
  46 * Naturally, the FULL state doesn't exist for the CPU resource at the
  47 * system level, but exist at the cgroup level. At the cgroup level,
  48 * FULL means all non-idle tasks in the cgroup are delayed on the CPU
  49 * resource which is being used by others outside of the cgroup or
  50 * throttled by the cgroup cpu.max configuration.
  51 *
  52 * The percentage of wall clock time spent in those compound stall
  53 * states gives pressure numbers between 0 and 100 for each resource,
  54 * where the SOME percentage indicates workload slowdowns and the FULL
  55 * percentage indicates reduced CPU utilization:
  56 *
  57 *	%SOME = time(SOME) / period
  58 *	%FULL = time(FULL) / period
  59 *
  60 *			Multiple CPUs
  61 *
  62 * The more tasks and available CPUs there are, the more work can be
  63 * performed concurrently. This means that the potential that can go
  64 * unrealized due to resource contention *also* scales with non-idle
  65 * tasks and CPUs.
  66 *
  67 * Consider a scenario where 257 number crunching tasks are trying to
  68 * run concurrently on 256 CPUs. If we simply aggregated the task
  69 * states, we would have to conclude a CPU SOME pressure number of
  70 * 100%, since *somebody* is waiting on a runqueue at all
  71 * times. However, that is clearly not the amount of contention the
  72 * workload is experiencing: only one out of 256 possible execution
  73 * threads will be contended at any given time, or about 0.4%.
  74 *
  75 * Conversely, consider a scenario of 4 tasks and 4 CPUs where at any
  76 * given time *one* of the tasks is delayed due to a lack of memory.
  77 * Again, looking purely at the task state would yield a memory FULL
  78 * pressure number of 0%, since *somebody* is always making forward
  79 * progress. But again this wouldn't capture the amount of execution
  80 * potential lost, which is 1 out of 4 CPUs, or 25%.
  81 *
  82 * To calculate wasted potential (pressure) with multiple processors,
  83 * we have to base our calculation on the number of non-idle tasks in
  84 * conjunction with the number of available CPUs, which is the number
  85 * of potential execution threads. SOME becomes then the proportion of
  86 * delayed tasks to possible threads, and FULL is the share of possible
  87 * threads that are unproductive due to delays:
  88 *
  89 *	threads = min(nr_nonidle_tasks, nr_cpus)
  90 *	   SOME = min(nr_delayed_tasks / threads, 1)
  91 *	   FULL = (threads - min(nr_productive_tasks, threads)) / threads
  92 *
  93 * For the 257 number crunchers on 256 CPUs, this yields:
  94 *
  95 *	threads = min(257, 256)
  96 *	   SOME = min(1 / 256, 1)             = 0.4%
  97 *	   FULL = (256 - min(256, 256)) / 256 = 0%
  98 *
  99 * For the 1 out of 4 memory-delayed tasks, this yields:
 100 *
 101 *	threads = min(4, 4)
 102 *	   SOME = min(1 / 4, 1)               = 25%
 103 *	   FULL = (4 - min(3, 4)) / 4         = 25%
 104 *
 105 * [ Substitute nr_cpus with 1, and you can see that it's a natural
 106 *   extension of the single-CPU model. ]
 107 *
 108 *			Implementation
 109 *
 110 * To assess the precise time spent in each such state, we would have
 111 * to freeze the system on task changes and start/stop the state
 112 * clocks accordingly. Obviously that doesn't scale in practice.
 113 *
 114 * Because the scheduler aims to distribute the compute load evenly
 115 * among the available CPUs, we can track task state locally to each
 116 * CPU and, at much lower frequency, extrapolate the global state for
 117 * the cumulative stall times and the running averages.
 118 *
 119 * For each runqueue, we track:
 120 *
 121 *	   tSOME[cpu] = time(nr_delayed_tasks[cpu] != 0)
 122 *	   tFULL[cpu] = time(nr_delayed_tasks[cpu] && !nr_productive_tasks[cpu])
 123 *	tNONIDLE[cpu] = time(nr_nonidle_tasks[cpu] != 0)
 124 *
 125 * and then periodically aggregate:
 126 *
 127 *	tNONIDLE = sum(tNONIDLE[i])
 128 *
 129 *	   tSOME = sum(tSOME[i] * tNONIDLE[i]) / tNONIDLE
 130 *	   tFULL = sum(tFULL[i] * tNONIDLE[i]) / tNONIDLE
 131 *
 132 *	   %SOME = tSOME / period
 133 *	   %FULL = tFULL / period
 134 *
 135 * This gives us an approximation of pressure that is practical
 136 * cost-wise, yet way more sensitive and accurate than periodic
 137 * sampling of the aggregate task states would be.
 138 */
 139
 140static int psi_bug __read_mostly;
 141
 142DEFINE_STATIC_KEY_FALSE(psi_disabled);
 143static DEFINE_STATIC_KEY_TRUE(psi_cgroups_enabled);
 144
 145#ifdef CONFIG_PSI_DEFAULT_DISABLED
 146static bool psi_enable;
 147#else
 148static bool psi_enable = true;
 149#endif
 150static int __init setup_psi(char *str)
 151{
 152	return kstrtobool(str, &psi_enable) == 0;
 153}
 154__setup("psi=", setup_psi);
 155
 156/* Running averages - we need to be higher-res than loadavg */
 157#define PSI_FREQ	(2*HZ+1)	/* 2 sec intervals */
 158#define EXP_10s		1677		/* 1/exp(2s/10s) as fixed-point */
 159#define EXP_60s		1981		/* 1/exp(2s/60s) */
 160#define EXP_300s	2034		/* 1/exp(2s/300s) */
 161
 162/* PSI trigger definitions */
 163#define WINDOW_MAX_US 10000000	/* Max window size is 10s */
 164#define UPDATES_PER_WINDOW 10	/* 10 updates per window */
 165
 166/* Sampling frequency in nanoseconds */
 167static u64 psi_period __read_mostly;
 168
 169/* System-level pressure and stall tracking */
 170static DEFINE_PER_CPU(struct psi_group_cpu, system_group_pcpu);
 171struct psi_group psi_system = {
 172	.pcpu = &system_group_pcpu,
 173};
 174
 175static void psi_avgs_work(struct work_struct *work);
 176
 177static void poll_timer_fn(struct timer_list *t);
 178
 179static void group_init(struct psi_group *group)
 180{
 181	int cpu;
 182
 183	group->enabled = true;
 184	for_each_possible_cpu(cpu)
 185		seqcount_init(&per_cpu_ptr(group->pcpu, cpu)->seq);
 186	group->avg_last_update = sched_clock();
 187	group->avg_next_update = group->avg_last_update + psi_period;
 188	mutex_init(&group->avgs_lock);
 189
 190	/* Init avg trigger-related members */
 191	INIT_LIST_HEAD(&group->avg_triggers);
 192	memset(group->avg_nr_triggers, 0, sizeof(group->avg_nr_triggers));
 193	INIT_DELAYED_WORK(&group->avgs_work, psi_avgs_work);
 194
 195	/* Init rtpoll trigger-related members */
 196	atomic_set(&group->rtpoll_scheduled, 0);
 197	mutex_init(&group->rtpoll_trigger_lock);
 198	INIT_LIST_HEAD(&group->rtpoll_triggers);
 199	group->rtpoll_min_period = U32_MAX;
 200	group->rtpoll_next_update = ULLONG_MAX;
 201	init_waitqueue_head(&group->rtpoll_wait);
 202	timer_setup(&group->rtpoll_timer, poll_timer_fn, 0);
 203	rcu_assign_pointer(group->rtpoll_task, NULL);
 204}
 205
 206void __init psi_init(void)
 207{
 208	if (!psi_enable) {
 209		static_branch_enable(&psi_disabled);
 210		static_branch_disable(&psi_cgroups_enabled);
 211		return;
 212	}
 213
 214	if (!cgroup_psi_enabled())
 215		static_branch_disable(&psi_cgroups_enabled);
 216
 217	psi_period = jiffies_to_nsecs(PSI_FREQ);
 218	group_init(&psi_system);
 219}
 220
 221static u32 test_states(unsigned int *tasks, u32 state_mask)
 222{
 223	const bool oncpu = state_mask & PSI_ONCPU;
 224
 225	if (tasks[NR_IOWAIT]) {
 226		state_mask |= BIT(PSI_IO_SOME);
 227		if (!tasks[NR_RUNNING])
 228			state_mask |= BIT(PSI_IO_FULL);
 229	}
 230
 231	if (tasks[NR_MEMSTALL]) {
 232		state_mask |= BIT(PSI_MEM_SOME);
 233		if (tasks[NR_RUNNING] == tasks[NR_MEMSTALL_RUNNING])
 234			state_mask |= BIT(PSI_MEM_FULL);
 
 
 
 
 
 
 
 235	}
 236
 237	if (tasks[NR_RUNNING] > oncpu)
 238		state_mask |= BIT(PSI_CPU_SOME);
 239
 240	if (tasks[NR_RUNNING] && !oncpu)
 241		state_mask |= BIT(PSI_CPU_FULL);
 242
 243	if (tasks[NR_IOWAIT] || tasks[NR_MEMSTALL] || tasks[NR_RUNNING])
 244		state_mask |= BIT(PSI_NONIDLE);
 245
 246	return state_mask;
 247}
 248
 249static void get_recent_times(struct psi_group *group, int cpu,
 250			     enum psi_aggregators aggregator, u32 *times,
 251			     u32 *pchanged_states)
 252{
 253	struct psi_group_cpu *groupc = per_cpu_ptr(group->pcpu, cpu);
 254	int current_cpu = raw_smp_processor_id();
 255	unsigned int tasks[NR_PSI_TASK_COUNTS];
 256	u64 now, state_start;
 257	enum psi_states s;
 258	unsigned int seq;
 259	u32 state_mask;
 260
 261	*pchanged_states = 0;
 262
 263	/* Snapshot a coherent view of the CPU state */
 264	do {
 265		seq = read_seqcount_begin(&groupc->seq);
 266		now = cpu_clock(cpu);
 267		memcpy(times, groupc->times, sizeof(groupc->times));
 268		state_mask = groupc->state_mask;
 269		state_start = groupc->state_start;
 270		if (cpu == current_cpu)
 271			memcpy(tasks, groupc->tasks, sizeof(groupc->tasks));
 272	} while (read_seqcount_retry(&groupc->seq, seq));
 273
 274	/* Calculate state time deltas against the previous snapshot */
 275	for (s = 0; s < NR_PSI_STATES; s++) {
 276		u32 delta;
 277		/*
 278		 * In addition to already concluded states, we also
 279		 * incorporate currently active states on the CPU,
 280		 * since states may last for many sampling periods.
 281		 *
 282		 * This way we keep our delta sampling buckets small
 283		 * (u32) and our reported pressure close to what's
 284		 * actually happening.
 285		 */
 286		if (state_mask & (1 << s))
 287			times[s] += now - state_start;
 288
 289		delta = times[s] - groupc->times_prev[aggregator][s];
 290		groupc->times_prev[aggregator][s] = times[s];
 291
 292		times[s] = delta;
 293		if (delta)
 294			*pchanged_states |= (1 << s);
 295	}
 296
 297	/*
 298	 * When collect_percpu_times() from the avgs_work, we don't want to
 299	 * re-arm avgs_work when all CPUs are IDLE. But the current CPU running
 300	 * this avgs_work is never IDLE, cause avgs_work can't be shut off.
 301	 * So for the current CPU, we need to re-arm avgs_work only when
 302	 * (NR_RUNNING > 1 || NR_IOWAIT > 0 || NR_MEMSTALL > 0), for other CPUs
 303	 * we can just check PSI_NONIDLE delta.
 304	 */
 305	if (current_work() == &group->avgs_work.work) {
 306		bool reschedule;
 307
 308		if (cpu == current_cpu)
 309			reschedule = tasks[NR_RUNNING] +
 310				     tasks[NR_IOWAIT] +
 311				     tasks[NR_MEMSTALL] > 1;
 312		else
 313			reschedule = *pchanged_states & (1 << PSI_NONIDLE);
 314
 315		if (reschedule)
 316			*pchanged_states |= PSI_STATE_RESCHEDULE;
 317	}
 318}
 319
 320static void calc_avgs(unsigned long avg[3], int missed_periods,
 321		      u64 time, u64 period)
 322{
 323	unsigned long pct;
 324
 325	/* Fill in zeroes for periods of no activity */
 326	if (missed_periods) {
 327		avg[0] = calc_load_n(avg[0], EXP_10s, 0, missed_periods);
 328		avg[1] = calc_load_n(avg[1], EXP_60s, 0, missed_periods);
 329		avg[2] = calc_load_n(avg[2], EXP_300s, 0, missed_periods);
 330	}
 331
 332	/* Sample the most recent active period */
 333	pct = div_u64(time * 100, period);
 334	pct *= FIXED_1;
 335	avg[0] = calc_load(avg[0], EXP_10s, pct);
 336	avg[1] = calc_load(avg[1], EXP_60s, pct);
 337	avg[2] = calc_load(avg[2], EXP_300s, pct);
 338}
 339
 340static void collect_percpu_times(struct psi_group *group,
 341				 enum psi_aggregators aggregator,
 342				 u32 *pchanged_states)
 343{
 344	u64 deltas[NR_PSI_STATES - 1] = { 0, };
 345	unsigned long nonidle_total = 0;
 346	u32 changed_states = 0;
 347	int cpu;
 348	int s;
 349
 350	/*
 351	 * Collect the per-cpu time buckets and average them into a
 352	 * single time sample that is normalized to wall clock time.
 353	 *
 354	 * For averaging, each CPU is weighted by its non-idle time in
 355	 * the sampling period. This eliminates artifacts from uneven
 356	 * loading, or even entirely idle CPUs.
 357	 */
 358	for_each_possible_cpu(cpu) {
 359		u32 times[NR_PSI_STATES];
 360		u32 nonidle;
 361		u32 cpu_changed_states;
 362
 363		get_recent_times(group, cpu, aggregator, times,
 364				&cpu_changed_states);
 365		changed_states |= cpu_changed_states;
 366
 367		nonidle = nsecs_to_jiffies(times[PSI_NONIDLE]);
 368		nonidle_total += nonidle;
 369
 370		for (s = 0; s < PSI_NONIDLE; s++)
 371			deltas[s] += (u64)times[s] * nonidle;
 372	}
 373
 374	/*
 375	 * Integrate the sample into the running statistics that are
 376	 * reported to userspace: the cumulative stall times and the
 377	 * decaying averages.
 378	 *
 379	 * Pressure percentages are sampled at PSI_FREQ. We might be
 380	 * called more often when the user polls more frequently than
 381	 * that; we might be called less often when there is no task
 382	 * activity, thus no data, and clock ticks are sporadic. The
 383	 * below handles both.
 384	 */
 385
 386	/* total= */
 387	for (s = 0; s < NR_PSI_STATES - 1; s++)
 388		group->total[aggregator][s] +=
 389				div_u64(deltas[s], max(nonidle_total, 1UL));
 390
 391	if (pchanged_states)
 392		*pchanged_states = changed_states;
 393}
 394
 395/* Trigger tracking window manipulations */
 396static void window_reset(struct psi_window *win, u64 now, u64 value,
 397			 u64 prev_growth)
 398{
 399	win->start_time = now;
 400	win->start_value = value;
 401	win->prev_growth = prev_growth;
 402}
 403
 404/*
 405 * PSI growth tracking window update and growth calculation routine.
 406 *
 407 * This approximates a sliding tracking window by interpolating
 408 * partially elapsed windows using historical growth data from the
 409 * previous intervals. This minimizes memory requirements (by not storing
 410 * all the intermediate values in the previous window) and simplifies
 411 * the calculations. It works well because PSI signal changes only in
 412 * positive direction and over relatively small window sizes the growth
 413 * is close to linear.
 414 */
 415static u64 window_update(struct psi_window *win, u64 now, u64 value)
 416{
 417	u64 elapsed;
 418	u64 growth;
 419
 420	elapsed = now - win->start_time;
 421	growth = value - win->start_value;
 422	/*
 423	 * After each tracking window passes win->start_value and
 424	 * win->start_time get reset and win->prev_growth stores
 425	 * the average per-window growth of the previous window.
 426	 * win->prev_growth is then used to interpolate additional
 427	 * growth from the previous window assuming it was linear.
 428	 */
 429	if (elapsed > win->size)
 430		window_reset(win, now, value, growth);
 431	else {
 432		u32 remaining;
 433
 434		remaining = win->size - elapsed;
 435		growth += div64_u64(win->prev_growth * remaining, win->size);
 436	}
 437
 438	return growth;
 439}
 440
 441static void update_triggers(struct psi_group *group, u64 now,
 442						   enum psi_aggregators aggregator)
 443{
 444	struct psi_trigger *t;
 445	u64 *total = group->total[aggregator];
 446	struct list_head *triggers;
 447	u64 *aggregator_total;
 448
 449	if (aggregator == PSI_AVGS) {
 450		triggers = &group->avg_triggers;
 451		aggregator_total = group->avg_total;
 452	} else {
 453		triggers = &group->rtpoll_triggers;
 454		aggregator_total = group->rtpoll_total;
 455	}
 456
 457	/*
 458	 * On subsequent updates, calculate growth deltas and let
 459	 * watchers know when their specified thresholds are exceeded.
 460	 */
 461	list_for_each_entry(t, triggers, node) {
 462		u64 growth;
 463		bool new_stall;
 464
 465		new_stall = aggregator_total[t->state] != total[t->state];
 466
 467		/* Check for stall activity or a previous threshold breach */
 468		if (!new_stall && !t->pending_event)
 469			continue;
 470		/*
 471		 * Check for new stall activity, as well as deferred
 472		 * events that occurred in the last window after the
 473		 * trigger had already fired (we want to ratelimit
 474		 * events without dropping any).
 475		 */
 476		if (new_stall) {
 477			/* Calculate growth since last update */
 478			growth = window_update(&t->win, now, total[t->state]);
 479			if (!t->pending_event) {
 480				if (growth < t->threshold)
 481					continue;
 482
 483				t->pending_event = true;
 484			}
 485		}
 486		/* Limit event signaling to once per window */
 487		if (now < t->last_event_time + t->win.size)
 488			continue;
 489
 490		/* Generate an event */
 491		if (cmpxchg(&t->event, 0, 1) == 0) {
 492			if (t->of)
 493				kernfs_notify(t->of->kn);
 494			else
 495				wake_up_interruptible(&t->event_wait);
 496		}
 497		t->last_event_time = now;
 498		/* Reset threshold breach flag once event got generated */
 499		t->pending_event = false;
 500	}
 501}
 502
 503static u64 update_averages(struct psi_group *group, u64 now)
 504{
 505	unsigned long missed_periods = 0;
 506	u64 expires, period;
 507	u64 avg_next_update;
 508	int s;
 509
 510	/* avgX= */
 511	expires = group->avg_next_update;
 512	if (now - expires >= psi_period)
 513		missed_periods = div_u64(now - expires, psi_period);
 514
 515	/*
 516	 * The periodic clock tick can get delayed for various
 517	 * reasons, especially on loaded systems. To avoid clock
 518	 * drift, we schedule the clock in fixed psi_period intervals.
 519	 * But the deltas we sample out of the per-cpu buckets above
 520	 * are based on the actual time elapsing between clock ticks.
 521	 */
 522	avg_next_update = expires + ((1 + missed_periods) * psi_period);
 523	period = now - (group->avg_last_update + (missed_periods * psi_period));
 524	group->avg_last_update = now;
 525
 526	for (s = 0; s < NR_PSI_STATES - 1; s++) {
 527		u32 sample;
 528
 529		sample = group->total[PSI_AVGS][s] - group->avg_total[s];
 530		/*
 531		 * Due to the lockless sampling of the time buckets,
 532		 * recorded time deltas can slip into the next period,
 533		 * which under full pressure can result in samples in
 534		 * excess of the period length.
 535		 *
 536		 * We don't want to report non-sensical pressures in
 537		 * excess of 100%, nor do we want to drop such events
 538		 * on the floor. Instead we punt any overage into the
 539		 * future until pressure subsides. By doing this we
 540		 * don't underreport the occurring pressure curve, we
 541		 * just report it delayed by one period length.
 542		 *
 543		 * The error isn't cumulative. As soon as another
 544		 * delta slips from a period P to P+1, by definition
 545		 * it frees up its time T in P.
 546		 */
 547		if (sample > period)
 548			sample = period;
 549		group->avg_total[s] += sample;
 550		calc_avgs(group->avg[s], missed_periods, sample, period);
 551	}
 552
 553	return avg_next_update;
 554}
 555
 556static void psi_avgs_work(struct work_struct *work)
 557{
 558	struct delayed_work *dwork;
 559	struct psi_group *group;
 560	u32 changed_states;
 561	u64 now;
 562
 563	dwork = to_delayed_work(work);
 564	group = container_of(dwork, struct psi_group, avgs_work);
 565
 566	mutex_lock(&group->avgs_lock);
 567
 568	now = sched_clock();
 569
 570	collect_percpu_times(group, PSI_AVGS, &changed_states);
 571	/*
 572	 * If there is task activity, periodically fold the per-cpu
 573	 * times and feed samples into the running averages. If things
 574	 * are idle and there is no data to process, stop the clock.
 575	 * Once restarted, we'll catch up the running averages in one
 576	 * go - see calc_avgs() and missed_periods.
 577	 */
 578	if (now >= group->avg_next_update) {
 579		update_triggers(group, now, PSI_AVGS);
 580		group->avg_next_update = update_averages(group, now);
 581	}
 582
 583	if (changed_states & PSI_STATE_RESCHEDULE) {
 584		schedule_delayed_work(dwork, nsecs_to_jiffies(
 585				group->avg_next_update - now) + 1);
 586	}
 587
 588	mutex_unlock(&group->avgs_lock);
 589}
 590
 591static void init_rtpoll_triggers(struct psi_group *group, u64 now)
 592{
 593	struct psi_trigger *t;
 594
 595	list_for_each_entry(t, &group->rtpoll_triggers, node)
 596		window_reset(&t->win, now,
 597				group->total[PSI_POLL][t->state], 0);
 598	memcpy(group->rtpoll_total, group->total[PSI_POLL],
 599		   sizeof(group->rtpoll_total));
 600	group->rtpoll_next_update = now + group->rtpoll_min_period;
 601}
 602
 603/* Schedule rtpolling if it's not already scheduled or forced. */
 604static void psi_schedule_rtpoll_work(struct psi_group *group, unsigned long delay,
 605				   bool force)
 606{
 607	struct task_struct *task;
 608
 609	/*
 610	 * atomic_xchg should be called even when !force to provide a
 611	 * full memory barrier (see the comment inside psi_rtpoll_work).
 612	 */
 613	if (atomic_xchg(&group->rtpoll_scheduled, 1) && !force)
 614		return;
 615
 616	rcu_read_lock();
 617
 618	task = rcu_dereference(group->rtpoll_task);
 619	/*
 620	 * kworker might be NULL in case psi_trigger_destroy races with
 621	 * psi_task_change (hotpath) which can't use locks
 622	 */
 623	if (likely(task))
 624		mod_timer(&group->rtpoll_timer, jiffies + delay);
 625	else
 626		atomic_set(&group->rtpoll_scheduled, 0);
 627
 628	rcu_read_unlock();
 629}
 630
 631static void psi_rtpoll_work(struct psi_group *group)
 632{
 633	bool force_reschedule = false;
 634	u32 changed_states;
 635	u64 now;
 636
 637	mutex_lock(&group->rtpoll_trigger_lock);
 638
 639	now = sched_clock();
 640
 641	if (now > group->rtpoll_until) {
 642		/*
 643		 * We are either about to start or might stop rtpolling if no
 644		 * state change was recorded. Resetting rtpoll_scheduled leaves
 645		 * a small window for psi_group_change to sneak in and schedule
 646		 * an immediate rtpoll_work before we get to rescheduling. One
 647		 * potential extra wakeup at the end of the rtpolling window
 648		 * should be negligible and rtpoll_next_update still keeps
 649		 * updates correctly on schedule.
 650		 */
 651		atomic_set(&group->rtpoll_scheduled, 0);
 652		/*
 653		 * A task change can race with the rtpoll worker that is supposed to
 654		 * report on it. To avoid missing events, ensure ordering between
 655		 * rtpoll_scheduled and the task state accesses, such that if the
 656		 * rtpoll worker misses the state update, the task change is
 657		 * guaranteed to reschedule the rtpoll worker:
 658		 *
 659		 * rtpoll worker:
 660		 *   atomic_set(rtpoll_scheduled, 0)
 661		 *   smp_mb()
 662		 *   LOAD states
 663		 *
 664		 * task change:
 665		 *   STORE states
 666		 *   if atomic_xchg(rtpoll_scheduled, 1) == 0:
 667		 *     schedule rtpoll worker
 668		 *
 669		 * The atomic_xchg() implies a full barrier.
 670		 */
 671		smp_mb();
 672	} else {
 673		/* The rtpolling window is not over, keep rescheduling */
 674		force_reschedule = true;
 675	}
 676
 677
 678	collect_percpu_times(group, PSI_POLL, &changed_states);
 679
 680	if (changed_states & group->rtpoll_states) {
 681		/* Initialize trigger windows when entering rtpolling mode */
 682		if (now > group->rtpoll_until)
 683			init_rtpoll_triggers(group, now);
 684
 685		/*
 686		 * Keep the monitor active for at least the duration of the
 687		 * minimum tracking window as long as monitor states are
 688		 * changing.
 689		 */
 690		group->rtpoll_until = now +
 691			group->rtpoll_min_period * UPDATES_PER_WINDOW;
 692	}
 693
 694	if (now > group->rtpoll_until) {
 695		group->rtpoll_next_update = ULLONG_MAX;
 696		goto out;
 697	}
 698
 699	if (now >= group->rtpoll_next_update) {
 700		if (changed_states & group->rtpoll_states) {
 701			update_triggers(group, now, PSI_POLL);
 702			memcpy(group->rtpoll_total, group->total[PSI_POLL],
 703				   sizeof(group->rtpoll_total));
 704		}
 705		group->rtpoll_next_update = now + group->rtpoll_min_period;
 706	}
 707
 708	psi_schedule_rtpoll_work(group,
 709		nsecs_to_jiffies(group->rtpoll_next_update - now) + 1,
 710		force_reschedule);
 711
 712out:
 713	mutex_unlock(&group->rtpoll_trigger_lock);
 714}
 715
 716static int psi_rtpoll_worker(void *data)
 717{
 718	struct psi_group *group = (struct psi_group *)data;
 719
 720	sched_set_fifo_low(current);
 721
 722	while (true) {
 723		wait_event_interruptible(group->rtpoll_wait,
 724				atomic_cmpxchg(&group->rtpoll_wakeup, 1, 0) ||
 725				kthread_should_stop());
 726		if (kthread_should_stop())
 727			break;
 728
 729		psi_rtpoll_work(group);
 730	}
 731	return 0;
 732}
 733
 734static void poll_timer_fn(struct timer_list *t)
 735{
 736	struct psi_group *group = from_timer(group, t, rtpoll_timer);
 737
 738	atomic_set(&group->rtpoll_wakeup, 1);
 739	wake_up_interruptible(&group->rtpoll_wait);
 740}
 741
 742static void record_times(struct psi_group_cpu *groupc, u64 now)
 743{
 744	u32 delta;
 745
 746	delta = now - groupc->state_start;
 747	groupc->state_start = now;
 748
 749	if (groupc->state_mask & (1 << PSI_IO_SOME)) {
 750		groupc->times[PSI_IO_SOME] += delta;
 751		if (groupc->state_mask & (1 << PSI_IO_FULL))
 752			groupc->times[PSI_IO_FULL] += delta;
 753	}
 754
 755	if (groupc->state_mask & (1 << PSI_MEM_SOME)) {
 756		groupc->times[PSI_MEM_SOME] += delta;
 757		if (groupc->state_mask & (1 << PSI_MEM_FULL))
 758			groupc->times[PSI_MEM_FULL] += delta;
 759	}
 760
 761	if (groupc->state_mask & (1 << PSI_CPU_SOME)) {
 762		groupc->times[PSI_CPU_SOME] += delta;
 763		if (groupc->state_mask & (1 << PSI_CPU_FULL))
 764			groupc->times[PSI_CPU_FULL] += delta;
 765	}
 766
 767	if (groupc->state_mask & (1 << PSI_NONIDLE))
 768		groupc->times[PSI_NONIDLE] += delta;
 769}
 770
 771static void psi_group_change(struct psi_group *group, int cpu,
 772			     unsigned int clear, unsigned int set,
 773			     bool wake_clock)
 774{
 775	struct psi_group_cpu *groupc;
 776	unsigned int t, m;
 
 777	u32 state_mask;
 778	u64 now;
 779
 780	lockdep_assert_rq_held(cpu_rq(cpu));
 781	groupc = per_cpu_ptr(group->pcpu, cpu);
 782
 783	/*
 784	 * First we update the task counts according to the state
 785	 * change requested through the @clear and @set bits.
 786	 *
 787	 * Then if the cgroup PSI stats accounting enabled, we
 788	 * assess the aggregate resource states this CPU's tasks
 789	 * have been in since the last change, and account any
 790	 * SOME and FULL time these may have resulted in.
 791	 */
 792	write_seqcount_begin(&groupc->seq);
 793	now = cpu_clock(cpu);
 794
 795	/*
 796	 * Start with TSK_ONCPU, which doesn't have a corresponding
 797	 * task count - it's just a boolean flag directly encoded in
 798	 * the state mask. Clear, set, or carry the current state if
 799	 * no changes are requested.
 800	 */
 801	if (unlikely(clear & TSK_ONCPU)) {
 802		state_mask = 0;
 803		clear &= ~TSK_ONCPU;
 804	} else if (unlikely(set & TSK_ONCPU)) {
 805		state_mask = PSI_ONCPU;
 806		set &= ~TSK_ONCPU;
 807	} else {
 808		state_mask = groupc->state_mask & PSI_ONCPU;
 809	}
 810
 811	/*
 812	 * The rest of the state mask is calculated based on the task
 813	 * counts. Update those first, then construct the mask.
 814	 */
 815	for (t = 0, m = clear; m; m &= ~(1 << t), t++) {
 816		if (!(m & (1 << t)))
 817			continue;
 818		if (groupc->tasks[t]) {
 819			groupc->tasks[t]--;
 820		} else if (!psi_bug) {
 821			printk_deferred(KERN_ERR "psi: task underflow! cpu=%d t=%d tasks=[%u %u %u %u] clear=%x set=%x\n",
 822					cpu, t, groupc->tasks[0],
 823					groupc->tasks[1], groupc->tasks[2],
 824					groupc->tasks[3], clear, set);
 825			psi_bug = 1;
 826		}
 827	}
 828
 829	for (t = 0; set; set &= ~(1 << t), t++)
 830		if (set & (1 << t))
 831			groupc->tasks[t]++;
 832
 833	if (!group->enabled) {
 834		/*
 835		 * On the first group change after disabling PSI, conclude
 836		 * the current state and flush its time. This is unlikely
 837		 * to matter to the user, but aggregation (get_recent_times)
 838		 * may have already incorporated the live state into times_prev;
 839		 * avoid a delta sample underflow when PSI is later re-enabled.
 840		 */
 841		if (unlikely(groupc->state_mask & (1 << PSI_NONIDLE)))
 842			record_times(groupc, now);
 843
 844		groupc->state_mask = state_mask;
 845
 846		write_seqcount_end(&groupc->seq);
 847		return;
 848	}
 849
 850	state_mask = test_states(groupc->tasks, state_mask);
 
 
 
 851
 852	/*
 853	 * Since we care about lost potential, a memstall is FULL
 854	 * when there are no other working tasks, but also when
 855	 * the CPU is actively reclaiming and nothing productive
 856	 * could run even if it were runnable. So when the current
 857	 * task in a cgroup is in_memstall, the corresponding groupc
 858	 * on that cpu is in PSI_MEM_FULL state.
 859	 */
 860	if (unlikely((state_mask & PSI_ONCPU) && cpu_curr(cpu)->in_memstall))
 861		state_mask |= (1 << PSI_MEM_FULL);
 862
 863	record_times(groupc, now);
 864
 865	groupc->state_mask = state_mask;
 866
 867	write_seqcount_end(&groupc->seq);
 868
 869	if (state_mask & group->rtpoll_states)
 870		psi_schedule_rtpoll_work(group, 1, false);
 871
 872	if (wake_clock && !delayed_work_pending(&group->avgs_work))
 873		schedule_delayed_work(&group->avgs_work, PSI_FREQ);
 874}
 875
 876static inline struct psi_group *task_psi_group(struct task_struct *task)
 877{
 878#ifdef CONFIG_CGROUPS
 879	if (static_branch_likely(&psi_cgroups_enabled))
 880		return cgroup_psi(task_dfl_cgroup(task));
 881#endif
 882	return &psi_system;
 883}
 884
 885static void psi_flags_change(struct task_struct *task, int clear, int set)
 886{
 887	if (((task->psi_flags & set) ||
 888	     (task->psi_flags & clear) != clear) &&
 889	    !psi_bug) {
 890		printk_deferred(KERN_ERR "psi: inconsistent task state! task=%d:%s cpu=%d psi_flags=%x clear=%x set=%x\n",
 891				task->pid, task->comm, task_cpu(task),
 892				task->psi_flags, clear, set);
 893		psi_bug = 1;
 894	}
 895
 896	task->psi_flags &= ~clear;
 897	task->psi_flags |= set;
 898}
 899
 900void psi_task_change(struct task_struct *task, int clear, int set)
 901{
 902	int cpu = task_cpu(task);
 903	struct psi_group *group;
 
 904
 905	if (!task->pid)
 906		return;
 907
 908	psi_flags_change(task, clear, set);
 909
 
 
 910	group = task_psi_group(task);
 911	do {
 912		psi_group_change(group, cpu, clear, set, true);
 913	} while ((group = group->parent));
 914}
 915
 916void psi_task_switch(struct task_struct *prev, struct task_struct *next,
 917		     bool sleep)
 918{
 919	struct psi_group *group, *common = NULL;
 920	int cpu = task_cpu(prev);
 
 921
 922	if (next->pid) {
 923		psi_flags_change(next, 0, TSK_ONCPU);
 924		/*
 925		 * Set TSK_ONCPU on @next's cgroups. If @next shares any
 926		 * ancestors with @prev, those will already have @prev's
 927		 * TSK_ONCPU bit set, and we can stop the iteration there.
 928		 */
 929		group = task_psi_group(next);
 930		do {
 931			if (per_cpu_ptr(group->pcpu, cpu)->state_mask &
 932			    PSI_ONCPU) {
 933				common = group;
 934				break;
 935			}
 936
 937			psi_group_change(group, cpu, 0, TSK_ONCPU, true);
 938		} while ((group = group->parent));
 939	}
 940
 941	if (prev->pid) {
 942		int clear = TSK_ONCPU, set = 0;
 943		bool wake_clock = true;
 944
 945		/*
 946		 * When we're going to sleep, psi_dequeue() lets us
 947		 * handle TSK_RUNNING, TSK_MEMSTALL_RUNNING and
 948		 * TSK_IOWAIT here, where we can combine it with
 949		 * TSK_ONCPU and save walking common ancestors twice.
 950		 */
 951		if (sleep) {
 952			clear |= TSK_RUNNING;
 953			if (prev->in_memstall)
 954				clear |= TSK_MEMSTALL_RUNNING;
 955			if (prev->in_iowait)
 956				set |= TSK_IOWAIT;
 957
 958			/*
 959			 * Periodic aggregation shuts off if there is a period of no
 960			 * task changes, so we wake it back up if necessary. However,
 961			 * don't do this if the task change is the aggregation worker
 962			 * itself going to sleep, or we'll ping-pong forever.
 963			 */
 964			if (unlikely((prev->flags & PF_WQ_WORKER) &&
 965				     wq_worker_last_func(prev) == psi_avgs_work))
 966				wake_clock = false;
 967		}
 968
 969		psi_flags_change(prev, clear, set);
 970
 971		group = task_psi_group(prev);
 972		do {
 973			if (group == common)
 974				break;
 975			psi_group_change(group, cpu, clear, set, wake_clock);
 976		} while ((group = group->parent));
 977
 978		/*
 979		 * TSK_ONCPU is handled up to the common ancestor. If there are
 980		 * any other differences between the two tasks (e.g. prev goes
 981		 * to sleep, or only one task is memstall), finish propagating
 982		 * those differences all the way up to the root.
 983		 */
 984		if ((prev->psi_flags ^ next->psi_flags) & ~TSK_ONCPU) {
 985			clear &= ~TSK_ONCPU;
 986			for (; group; group = group->parent)
 987				psi_group_change(group, cpu, clear, set, wake_clock);
 988		}
 989	}
 990}
 991
 992#ifdef CONFIG_IRQ_TIME_ACCOUNTING
 993void psi_account_irqtime(struct rq *rq, struct task_struct *curr, struct task_struct *prev)
 994{
 995	int cpu = task_cpu(curr);
 996	struct psi_group *group;
 997	struct psi_group_cpu *groupc;
 998	s64 delta;
 999	u64 irq;
1000
1001	if (static_branch_likely(&psi_disabled))
1002		return;
1003
1004	if (!curr->pid)
1005		return;
1006
1007	lockdep_assert_rq_held(rq);
1008	group = task_psi_group(curr);
1009	if (prev && task_psi_group(prev) == group)
1010		return;
1011
1012	irq = irq_time_read(cpu);
1013	delta = (s64)(irq - rq->psi_irq_time);
1014	if (delta < 0)
1015		return;
1016	rq->psi_irq_time = irq;
1017
 
1018	do {
1019		u64 now;
1020
1021		if (!group->enabled)
1022			continue;
1023
1024		groupc = per_cpu_ptr(group->pcpu, cpu);
1025
1026		write_seqcount_begin(&groupc->seq);
1027		now = cpu_clock(cpu);
1028
1029		record_times(groupc, now);
1030		groupc->times[PSI_IRQ_FULL] += delta;
1031
1032		write_seqcount_end(&groupc->seq);
1033
1034		if (group->rtpoll_states & (1 << PSI_IRQ_FULL))
1035			psi_schedule_rtpoll_work(group, 1, false);
1036	} while ((group = group->parent));
1037}
1038#endif
1039
1040/**
1041 * psi_memstall_enter - mark the beginning of a memory stall section
1042 * @flags: flags to handle nested sections
1043 *
1044 * Marks the calling task as being stalled due to a lack of memory,
1045 * such as waiting for a refault or performing reclaim.
1046 */
1047void psi_memstall_enter(unsigned long *flags)
1048{
1049	struct rq_flags rf;
1050	struct rq *rq;
1051
1052	if (static_branch_likely(&psi_disabled))
1053		return;
1054
1055	*flags = current->in_memstall;
1056	if (*flags)
1057		return;
1058	/*
1059	 * in_memstall setting & accounting needs to be atomic wrt
1060	 * changes to the task's scheduling state, otherwise we can
1061	 * race with CPU migration.
1062	 */
1063	rq = this_rq_lock_irq(&rf);
1064
1065	current->in_memstall = 1;
1066	psi_task_change(current, 0, TSK_MEMSTALL | TSK_MEMSTALL_RUNNING);
1067
1068	rq_unlock_irq(rq, &rf);
1069}
1070EXPORT_SYMBOL_GPL(psi_memstall_enter);
1071
1072/**
1073 * psi_memstall_leave - mark the end of an memory stall section
1074 * @flags: flags to handle nested memdelay sections
1075 *
1076 * Marks the calling task as no longer stalled due to lack of memory.
1077 */
1078void psi_memstall_leave(unsigned long *flags)
1079{
1080	struct rq_flags rf;
1081	struct rq *rq;
1082
1083	if (static_branch_likely(&psi_disabled))
1084		return;
1085
1086	if (*flags)
1087		return;
1088	/*
1089	 * in_memstall clearing & accounting needs to be atomic wrt
1090	 * changes to the task's scheduling state, otherwise we could
1091	 * race with CPU migration.
1092	 */
1093	rq = this_rq_lock_irq(&rf);
1094
1095	current->in_memstall = 0;
1096	psi_task_change(current, TSK_MEMSTALL | TSK_MEMSTALL_RUNNING, 0);
1097
1098	rq_unlock_irq(rq, &rf);
1099}
1100EXPORT_SYMBOL_GPL(psi_memstall_leave);
1101
1102#ifdef CONFIG_CGROUPS
1103int psi_cgroup_alloc(struct cgroup *cgroup)
1104{
1105	if (!static_branch_likely(&psi_cgroups_enabled))
1106		return 0;
1107
1108	cgroup->psi = kzalloc(sizeof(struct psi_group), GFP_KERNEL);
1109	if (!cgroup->psi)
1110		return -ENOMEM;
1111
1112	cgroup->psi->pcpu = alloc_percpu(struct psi_group_cpu);
1113	if (!cgroup->psi->pcpu) {
1114		kfree(cgroup->psi);
1115		return -ENOMEM;
1116	}
1117	group_init(cgroup->psi);
1118	cgroup->psi->parent = cgroup_psi(cgroup_parent(cgroup));
1119	return 0;
1120}
1121
1122void psi_cgroup_free(struct cgroup *cgroup)
1123{
1124	if (!static_branch_likely(&psi_cgroups_enabled))
1125		return;
1126
1127	cancel_delayed_work_sync(&cgroup->psi->avgs_work);
1128	free_percpu(cgroup->psi->pcpu);
1129	/* All triggers must be removed by now */
1130	WARN_ONCE(cgroup->psi->rtpoll_states, "psi: trigger leak\n");
1131	kfree(cgroup->psi);
1132}
1133
1134/**
1135 * cgroup_move_task - move task to a different cgroup
1136 * @task: the task
1137 * @to: the target css_set
1138 *
1139 * Move task to a new cgroup and safely migrate its associated stall
1140 * state between the different groups.
1141 *
1142 * This function acquires the task's rq lock to lock out concurrent
1143 * changes to the task's scheduling state and - in case the task is
1144 * running - concurrent changes to its stall state.
1145 */
1146void cgroup_move_task(struct task_struct *task, struct css_set *to)
1147{
1148	unsigned int task_flags;
1149	struct rq_flags rf;
1150	struct rq *rq;
1151
1152	if (!static_branch_likely(&psi_cgroups_enabled)) {
1153		/*
1154		 * Lame to do this here, but the scheduler cannot be locked
1155		 * from the outside, so we move cgroups from inside sched/.
1156		 */
1157		rcu_assign_pointer(task->cgroups, to);
1158		return;
1159	}
1160
1161	rq = task_rq_lock(task, &rf);
1162
1163	/*
1164	 * We may race with schedule() dropping the rq lock between
1165	 * deactivating prev and switching to next. Because the psi
1166	 * updates from the deactivation are deferred to the switch
1167	 * callback to save cgroup tree updates, the task's scheduling
1168	 * state here is not coherent with its psi state:
1169	 *
1170	 * schedule()                   cgroup_move_task()
1171	 *   rq_lock()
1172	 *   deactivate_task()
1173	 *     p->on_rq = 0
1174	 *     psi_dequeue() // defers TSK_RUNNING & TSK_IOWAIT updates
1175	 *   pick_next_task()
1176	 *     rq_unlock()
1177	 *                                rq_lock()
1178	 *                                psi_task_change() // old cgroup
1179	 *                                task->cgroups = to
1180	 *                                psi_task_change() // new cgroup
1181	 *                                rq_unlock()
1182	 *     rq_lock()
1183	 *   psi_sched_switch() // does deferred updates in new cgroup
1184	 *
1185	 * Don't rely on the scheduling state. Use psi_flags instead.
1186	 */
1187	task_flags = task->psi_flags;
1188
1189	if (task_flags)
1190		psi_task_change(task, task_flags, 0);
1191
1192	/* See comment above */
1193	rcu_assign_pointer(task->cgroups, to);
1194
1195	if (task_flags)
1196		psi_task_change(task, 0, task_flags);
1197
1198	task_rq_unlock(rq, task, &rf);
1199}
1200
1201void psi_cgroup_restart(struct psi_group *group)
1202{
1203	int cpu;
1204
1205	/*
1206	 * After we disable psi_group->enabled, we don't actually
1207	 * stop percpu tasks accounting in each psi_group_cpu,
1208	 * instead only stop test_states() loop, record_times()
1209	 * and averaging worker, see psi_group_change() for details.
1210	 *
1211	 * When disable cgroup PSI, this function has nothing to sync
1212	 * since cgroup pressure files are hidden and percpu psi_group_cpu
1213	 * would see !psi_group->enabled and only do task accounting.
1214	 *
1215	 * When re-enable cgroup PSI, this function use psi_group_change()
1216	 * to get correct state mask from test_states() loop on tasks[],
1217	 * and restart groupc->state_start from now, use .clear = .set = 0
1218	 * here since no task status really changed.
1219	 */
1220	if (!group->enabled)
1221		return;
1222
1223	for_each_possible_cpu(cpu) {
1224		struct rq *rq = cpu_rq(cpu);
1225		struct rq_flags rf;
 
1226
1227		rq_lock_irq(rq, &rf);
1228		psi_group_change(group, cpu, 0, 0, true);
 
1229		rq_unlock_irq(rq, &rf);
1230	}
1231}
1232#endif /* CONFIG_CGROUPS */
1233
1234int psi_show(struct seq_file *m, struct psi_group *group, enum psi_res res)
1235{
1236	bool only_full = false;
1237	int full;
1238	u64 now;
1239
1240	if (static_branch_likely(&psi_disabled))
1241		return -EOPNOTSUPP;
1242
1243	/* Update averages before reporting them */
1244	mutex_lock(&group->avgs_lock);
1245	now = sched_clock();
1246	collect_percpu_times(group, PSI_AVGS, NULL);
1247	if (now >= group->avg_next_update)
1248		group->avg_next_update = update_averages(group, now);
1249	mutex_unlock(&group->avgs_lock);
1250
1251#ifdef CONFIG_IRQ_TIME_ACCOUNTING
1252	only_full = res == PSI_IRQ;
1253#endif
1254
1255	for (full = 0; full < 2 - only_full; full++) {
1256		unsigned long avg[3] = { 0, };
1257		u64 total = 0;
1258		int w;
1259
1260		/* CPU FULL is undefined at the system level */
1261		if (!(group == &psi_system && res == PSI_CPU && full)) {
1262			for (w = 0; w < 3; w++)
1263				avg[w] = group->avg[res * 2 + full][w];
1264			total = div_u64(group->total[PSI_AVGS][res * 2 + full],
1265					NSEC_PER_USEC);
1266		}
1267
1268		seq_printf(m, "%s avg10=%lu.%02lu avg60=%lu.%02lu avg300=%lu.%02lu total=%llu\n",
1269			   full || only_full ? "full" : "some",
1270			   LOAD_INT(avg[0]), LOAD_FRAC(avg[0]),
1271			   LOAD_INT(avg[1]), LOAD_FRAC(avg[1]),
1272			   LOAD_INT(avg[2]), LOAD_FRAC(avg[2]),
1273			   total);
1274	}
1275
1276	return 0;
1277}
1278
1279struct psi_trigger *psi_trigger_create(struct psi_group *group, char *buf,
1280				       enum psi_res res, struct file *file,
1281				       struct kernfs_open_file *of)
1282{
1283	struct psi_trigger *t;
1284	enum psi_states state;
1285	u32 threshold_us;
1286	bool privileged;
1287	u32 window_us;
1288
1289	if (static_branch_likely(&psi_disabled))
1290		return ERR_PTR(-EOPNOTSUPP);
1291
1292	/*
1293	 * Checking the privilege here on file->f_cred implies that a privileged user
1294	 * could open the file and delegate the write to an unprivileged one.
1295	 */
1296	privileged = cap_raised(file->f_cred->cap_effective, CAP_SYS_RESOURCE);
1297
1298	if (sscanf(buf, "some %u %u", &threshold_us, &window_us) == 2)
1299		state = PSI_IO_SOME + res * 2;
1300	else if (sscanf(buf, "full %u %u", &threshold_us, &window_us) == 2)
1301		state = PSI_IO_FULL + res * 2;
1302	else
1303		return ERR_PTR(-EINVAL);
1304
1305#ifdef CONFIG_IRQ_TIME_ACCOUNTING
1306	if (res == PSI_IRQ && --state != PSI_IRQ_FULL)
1307		return ERR_PTR(-EINVAL);
1308#endif
1309
1310	if (state >= PSI_NONIDLE)
1311		return ERR_PTR(-EINVAL);
1312
1313	if (window_us == 0 || window_us > WINDOW_MAX_US)
1314		return ERR_PTR(-EINVAL);
1315
1316	/*
1317	 * Unprivileged users can only use 2s windows so that averages aggregation
1318	 * work is used, and no RT threads need to be spawned.
1319	 */
1320	if (!privileged && window_us % 2000000)
1321		return ERR_PTR(-EINVAL);
1322
1323	/* Check threshold */
1324	if (threshold_us == 0 || threshold_us > window_us)
1325		return ERR_PTR(-EINVAL);
1326
1327	t = kmalloc(sizeof(*t), GFP_KERNEL);
1328	if (!t)
1329		return ERR_PTR(-ENOMEM);
1330
1331	t->group = group;
1332	t->state = state;
1333	t->threshold = threshold_us * NSEC_PER_USEC;
1334	t->win.size = window_us * NSEC_PER_USEC;
1335	window_reset(&t->win, sched_clock(),
1336			group->total[PSI_POLL][t->state], 0);
1337
1338	t->event = 0;
1339	t->last_event_time = 0;
1340	t->of = of;
1341	if (!of)
1342		init_waitqueue_head(&t->event_wait);
1343	t->pending_event = false;
1344	t->aggregator = privileged ? PSI_POLL : PSI_AVGS;
1345
1346	if (privileged) {
1347		mutex_lock(&group->rtpoll_trigger_lock);
1348
1349		if (!rcu_access_pointer(group->rtpoll_task)) {
1350			struct task_struct *task;
1351
1352			task = kthread_create(psi_rtpoll_worker, group, "psimon");
1353			if (IS_ERR(task)) {
1354				kfree(t);
1355				mutex_unlock(&group->rtpoll_trigger_lock);
1356				return ERR_CAST(task);
1357			}
1358			atomic_set(&group->rtpoll_wakeup, 0);
1359			wake_up_process(task);
1360			rcu_assign_pointer(group->rtpoll_task, task);
1361		}
1362
1363		list_add(&t->node, &group->rtpoll_triggers);
1364		group->rtpoll_min_period = min(group->rtpoll_min_period,
1365			div_u64(t->win.size, UPDATES_PER_WINDOW));
1366		group->rtpoll_nr_triggers[t->state]++;
1367		group->rtpoll_states |= (1 << t->state);
1368
1369		mutex_unlock(&group->rtpoll_trigger_lock);
1370	} else {
1371		mutex_lock(&group->avgs_lock);
1372
1373		list_add(&t->node, &group->avg_triggers);
1374		group->avg_nr_triggers[t->state]++;
1375
1376		mutex_unlock(&group->avgs_lock);
1377	}
1378	return t;
1379}
1380
1381void psi_trigger_destroy(struct psi_trigger *t)
1382{
1383	struct psi_group *group;
1384	struct task_struct *task_to_destroy = NULL;
1385
1386	/*
1387	 * We do not check psi_disabled since it might have been disabled after
1388	 * the trigger got created.
1389	 */
1390	if (!t)
1391		return;
1392
1393	group = t->group;
1394	/*
1395	 * Wakeup waiters to stop polling and clear the queue to prevent it from
1396	 * being accessed later. Can happen if cgroup is deleted from under a
1397	 * polling process.
1398	 */
1399	if (t->of)
1400		kernfs_notify(t->of->kn);
1401	else
1402		wake_up_interruptible(&t->event_wait);
1403
1404	if (t->aggregator == PSI_AVGS) {
1405		mutex_lock(&group->avgs_lock);
1406		if (!list_empty(&t->node)) {
1407			list_del(&t->node);
1408			group->avg_nr_triggers[t->state]--;
1409		}
1410		mutex_unlock(&group->avgs_lock);
1411	} else {
1412		mutex_lock(&group->rtpoll_trigger_lock);
1413		if (!list_empty(&t->node)) {
1414			struct psi_trigger *tmp;
1415			u64 period = ULLONG_MAX;
1416
1417			list_del(&t->node);
1418			group->rtpoll_nr_triggers[t->state]--;
1419			if (!group->rtpoll_nr_triggers[t->state])
1420				group->rtpoll_states &= ~(1 << t->state);
1421			/*
1422			 * Reset min update period for the remaining triggers
1423			 * iff the destroying trigger had the min window size.
1424			 */
1425			if (group->rtpoll_min_period == div_u64(t->win.size, UPDATES_PER_WINDOW)) {
1426				list_for_each_entry(tmp, &group->rtpoll_triggers, node)
1427					period = min(period, div_u64(tmp->win.size,
1428							UPDATES_PER_WINDOW));
1429				group->rtpoll_min_period = period;
1430			}
1431			/* Destroy rtpoll_task when the last trigger is destroyed */
1432			if (group->rtpoll_states == 0) {
1433				group->rtpoll_until = 0;
1434				task_to_destroy = rcu_dereference_protected(
1435						group->rtpoll_task,
1436						lockdep_is_held(&group->rtpoll_trigger_lock));
1437				rcu_assign_pointer(group->rtpoll_task, NULL);
1438				del_timer(&group->rtpoll_timer);
1439			}
1440		}
1441		mutex_unlock(&group->rtpoll_trigger_lock);
1442	}
1443
1444	/*
1445	 * Wait for psi_schedule_rtpoll_work RCU to complete its read-side
1446	 * critical section before destroying the trigger and optionally the
1447	 * rtpoll_task.
1448	 */
1449	synchronize_rcu();
1450	/*
1451	 * Stop kthread 'psimon' after releasing rtpoll_trigger_lock to prevent
1452	 * a deadlock while waiting for psi_rtpoll_work to acquire
1453	 * rtpoll_trigger_lock
1454	 */
1455	if (task_to_destroy) {
1456		/*
1457		 * After the RCU grace period has expired, the worker
1458		 * can no longer be found through group->rtpoll_task.
1459		 */
1460		kthread_stop(task_to_destroy);
1461		atomic_set(&group->rtpoll_scheduled, 0);
1462	}
1463	kfree(t);
1464}
1465
1466__poll_t psi_trigger_poll(void **trigger_ptr,
1467				struct file *file, poll_table *wait)
1468{
1469	__poll_t ret = DEFAULT_POLLMASK;
1470	struct psi_trigger *t;
1471
1472	if (static_branch_likely(&psi_disabled))
1473		return DEFAULT_POLLMASK | EPOLLERR | EPOLLPRI;
1474
1475	t = smp_load_acquire(trigger_ptr);
1476	if (!t)
1477		return DEFAULT_POLLMASK | EPOLLERR | EPOLLPRI;
1478
1479	if (t->of)
1480		kernfs_generic_poll(t->of, wait);
1481	else
1482		poll_wait(file, &t->event_wait, wait);
1483
1484	if (cmpxchg(&t->event, 1, 0) == 1)
1485		ret |= EPOLLPRI;
1486
1487	return ret;
1488}
1489
1490#ifdef CONFIG_PROC_FS
1491static int psi_io_show(struct seq_file *m, void *v)
1492{
1493	return psi_show(m, &psi_system, PSI_IO);
1494}
1495
1496static int psi_memory_show(struct seq_file *m, void *v)
1497{
1498	return psi_show(m, &psi_system, PSI_MEM);
1499}
1500
1501static int psi_cpu_show(struct seq_file *m, void *v)
1502{
1503	return psi_show(m, &psi_system, PSI_CPU);
1504}
1505
1506static int psi_io_open(struct inode *inode, struct file *file)
1507{
1508	return single_open(file, psi_io_show, NULL);
1509}
1510
1511static int psi_memory_open(struct inode *inode, struct file *file)
1512{
1513	return single_open(file, psi_memory_show, NULL);
1514}
1515
1516static int psi_cpu_open(struct inode *inode, struct file *file)
1517{
1518	return single_open(file, psi_cpu_show, NULL);
1519}
1520
1521static ssize_t psi_write(struct file *file, const char __user *user_buf,
1522			 size_t nbytes, enum psi_res res)
1523{
1524	char buf[32];
1525	size_t buf_size;
1526	struct seq_file *seq;
1527	struct psi_trigger *new;
1528
1529	if (static_branch_likely(&psi_disabled))
1530		return -EOPNOTSUPP;
1531
1532	if (!nbytes)
1533		return -EINVAL;
1534
1535	buf_size = min(nbytes, sizeof(buf));
1536	if (copy_from_user(buf, user_buf, buf_size))
1537		return -EFAULT;
1538
1539	buf[buf_size - 1] = '\0';
1540
1541	seq = file->private_data;
1542
1543	/* Take seq->lock to protect seq->private from concurrent writes */
1544	mutex_lock(&seq->lock);
1545
1546	/* Allow only one trigger per file descriptor */
1547	if (seq->private) {
1548		mutex_unlock(&seq->lock);
1549		return -EBUSY;
1550	}
1551
1552	new = psi_trigger_create(&psi_system, buf, res, file, NULL);
1553	if (IS_ERR(new)) {
1554		mutex_unlock(&seq->lock);
1555		return PTR_ERR(new);
1556	}
1557
1558	smp_store_release(&seq->private, new);
1559	mutex_unlock(&seq->lock);
1560
1561	return nbytes;
1562}
1563
1564static ssize_t psi_io_write(struct file *file, const char __user *user_buf,
1565			    size_t nbytes, loff_t *ppos)
1566{
1567	return psi_write(file, user_buf, nbytes, PSI_IO);
1568}
1569
1570static ssize_t psi_memory_write(struct file *file, const char __user *user_buf,
1571				size_t nbytes, loff_t *ppos)
1572{
1573	return psi_write(file, user_buf, nbytes, PSI_MEM);
1574}
1575
1576static ssize_t psi_cpu_write(struct file *file, const char __user *user_buf,
1577			     size_t nbytes, loff_t *ppos)
1578{
1579	return psi_write(file, user_buf, nbytes, PSI_CPU);
1580}
1581
1582static __poll_t psi_fop_poll(struct file *file, poll_table *wait)
1583{
1584	struct seq_file *seq = file->private_data;
1585
1586	return psi_trigger_poll(&seq->private, file, wait);
1587}
1588
1589static int psi_fop_release(struct inode *inode, struct file *file)
1590{
1591	struct seq_file *seq = file->private_data;
1592
1593	psi_trigger_destroy(seq->private);
1594	return single_release(inode, file);
1595}
1596
1597static const struct proc_ops psi_io_proc_ops = {
1598	.proc_open	= psi_io_open,
1599	.proc_read	= seq_read,
1600	.proc_lseek	= seq_lseek,
1601	.proc_write	= psi_io_write,
1602	.proc_poll	= psi_fop_poll,
1603	.proc_release	= psi_fop_release,
1604};
1605
1606static const struct proc_ops psi_memory_proc_ops = {
1607	.proc_open	= psi_memory_open,
1608	.proc_read	= seq_read,
1609	.proc_lseek	= seq_lseek,
1610	.proc_write	= psi_memory_write,
1611	.proc_poll	= psi_fop_poll,
1612	.proc_release	= psi_fop_release,
1613};
1614
1615static const struct proc_ops psi_cpu_proc_ops = {
1616	.proc_open	= psi_cpu_open,
1617	.proc_read	= seq_read,
1618	.proc_lseek	= seq_lseek,
1619	.proc_write	= psi_cpu_write,
1620	.proc_poll	= psi_fop_poll,
1621	.proc_release	= psi_fop_release,
1622};
1623
1624#ifdef CONFIG_IRQ_TIME_ACCOUNTING
1625static int psi_irq_show(struct seq_file *m, void *v)
1626{
1627	return psi_show(m, &psi_system, PSI_IRQ);
1628}
1629
1630static int psi_irq_open(struct inode *inode, struct file *file)
1631{
1632	return single_open(file, psi_irq_show, NULL);
1633}
1634
1635static ssize_t psi_irq_write(struct file *file, const char __user *user_buf,
1636			     size_t nbytes, loff_t *ppos)
1637{
1638	return psi_write(file, user_buf, nbytes, PSI_IRQ);
1639}
1640
1641static const struct proc_ops psi_irq_proc_ops = {
1642	.proc_open	= psi_irq_open,
1643	.proc_read	= seq_read,
1644	.proc_lseek	= seq_lseek,
1645	.proc_write	= psi_irq_write,
1646	.proc_poll	= psi_fop_poll,
1647	.proc_release	= psi_fop_release,
1648};
1649#endif
1650
1651static int __init psi_proc_init(void)
1652{
1653	if (psi_enable) {
1654		proc_mkdir("pressure", NULL);
1655		proc_create("pressure/io", 0666, NULL, &psi_io_proc_ops);
1656		proc_create("pressure/memory", 0666, NULL, &psi_memory_proc_ops);
1657		proc_create("pressure/cpu", 0666, NULL, &psi_cpu_proc_ops);
1658#ifdef CONFIG_IRQ_TIME_ACCOUNTING
1659		proc_create("pressure/irq", 0666, NULL, &psi_irq_proc_ops);
1660#endif
1661	}
1662	return 0;
1663}
1664module_init(psi_proc_init);
1665
1666#endif /* CONFIG_PROC_FS */