1 // SPDX-License-Identifier: GPL-2.0-or-later 1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /* 2 /*
3 * kernel/stop_machine.c 3 * kernel/stop_machine.c
4 * 4 *
5 * Copyright (C) 2008, 2005 IBM Corporatio 5 * Copyright (C) 2008, 2005 IBM Corporation.
6 * Copyright (C) 2008, 2005 Rusty Russell 6 * Copyright (C) 2008, 2005 Rusty Russell rusty@rustcorp.com.au
7 * Copyright (C) 2010 SUSE Linux Pro 7 * Copyright (C) 2010 SUSE Linux Products GmbH
8 * Copyright (C) 2010 Tejun Heo <tj@ 8 * Copyright (C) 2010 Tejun Heo <tj@kernel.org>
9 */ 9 */
10 #include <linux/compiler.h> 10 #include <linux/compiler.h>
11 #include <linux/completion.h> 11 #include <linux/completion.h>
12 #include <linux/cpu.h> 12 #include <linux/cpu.h>
13 #include <linux/init.h> 13 #include <linux/init.h>
14 #include <linux/kthread.h> 14 #include <linux/kthread.h>
15 #include <linux/export.h> 15 #include <linux/export.h>
16 #include <linux/percpu.h> 16 #include <linux/percpu.h>
17 #include <linux/sched.h> 17 #include <linux/sched.h>
18 #include <linux/stop_machine.h> 18 #include <linux/stop_machine.h>
19 #include <linux/interrupt.h> 19 #include <linux/interrupt.h>
20 #include <linux/kallsyms.h> 20 #include <linux/kallsyms.h>
21 #include <linux/smpboot.h> 21 #include <linux/smpboot.h>
22 #include <linux/atomic.h> 22 #include <linux/atomic.h>
23 #include <linux/nmi.h> 23 #include <linux/nmi.h>
24 #include <linux/sched/wake_q.h> 24 #include <linux/sched/wake_q.h>
25 25
26 /* 26 /*
27 * Structure to determine completion condition 27 * Structure to determine completion condition and record errors. May
28 * be shared by works on different cpus. 28 * be shared by works on different cpus.
29 */ 29 */
30 struct cpu_stop_done { 30 struct cpu_stop_done {
31 atomic_t nr_todo; 31 atomic_t nr_todo; /* nr left to execute */
32 int ret; 32 int ret; /* collected return value */
33 struct completion completion; 33 struct completion completion; /* fired if nr_todo reaches 0 */
34 }; 34 };
35 35
36 /* the actual stopper, one per every possible 36 /* the actual stopper, one per every possible cpu, enabled on online cpus */
37 struct cpu_stopper { 37 struct cpu_stopper {
38 struct task_struct *thread; 38 struct task_struct *thread;
39 39
40 raw_spinlock_t lock; 40 raw_spinlock_t lock;
41 bool enabled; 41 bool enabled; /* is this stopper enabled? */
42 struct list_head works; 42 struct list_head works; /* list of pending works */
43 43
44 struct cpu_stop_work stop_work; 44 struct cpu_stop_work stop_work; /* for stop_cpus */
45 unsigned long caller; <<
46 cpu_stop_fn_t fn; <<
47 }; 45 };
48 46
49 static DEFINE_PER_CPU(struct cpu_stopper, cpu_ 47 static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper);
50 static bool stop_machine_initialized = false; 48 static bool stop_machine_initialized = false;
51 49
52 void print_stop_info(const char *log_lvl, stru <<
53 { <<
54 /* <<
55 * If @task is a stopper task, it cann <<
56 * stable. <<
57 */ <<
58 struct cpu_stopper *stopper = per_cpu_ <<
59 <<
60 if (task != stopper->thread) <<
61 return; <<
62 <<
63 printk("%sStopper: %pS <- %pS\n", log_ <<
64 } <<
65 <<
66 /* static data for stop_cpus */ 50 /* static data for stop_cpus */
67 static DEFINE_MUTEX(stop_cpus_mutex); 51 static DEFINE_MUTEX(stop_cpus_mutex);
68 static bool stop_cpus_in_progress; 52 static bool stop_cpus_in_progress;
69 53
70 static void cpu_stop_init_done(struct cpu_stop 54 static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo)
71 { 55 {
72 memset(done, 0, sizeof(*done)); 56 memset(done, 0, sizeof(*done));
73 atomic_set(&done->nr_todo, nr_todo); 57 atomic_set(&done->nr_todo, nr_todo);
74 init_completion(&done->completion); 58 init_completion(&done->completion);
75 } 59 }
76 60
77 /* signal completion unless @done is NULL */ 61 /* signal completion unless @done is NULL */
78 static void cpu_stop_signal_done(struct cpu_st 62 static void cpu_stop_signal_done(struct cpu_stop_done *done)
79 { 63 {
80 if (atomic_dec_and_test(&done->nr_todo 64 if (atomic_dec_and_test(&done->nr_todo))
81 complete(&done->completion); 65 complete(&done->completion);
82 } 66 }
83 67
84 static void __cpu_stop_queue_work(struct cpu_s 68 static void __cpu_stop_queue_work(struct cpu_stopper *stopper,
85 struct 69 struct cpu_stop_work *work,
86 struct 70 struct wake_q_head *wakeq)
87 { 71 {
88 list_add_tail(&work->list, &stopper->w 72 list_add_tail(&work->list, &stopper->works);
89 wake_q_add(wakeq, stopper->thread); 73 wake_q_add(wakeq, stopper->thread);
90 } 74 }
91 75
92 /* queue @work to @stopper. if offline, @work 76 /* queue @work to @stopper. if offline, @work is completed immediately */
93 static bool cpu_stop_queue_work(unsigned int c 77 static bool cpu_stop_queue_work(unsigned int cpu, struct cpu_stop_work *work)
94 { 78 {
95 struct cpu_stopper *stopper = &per_cpu 79 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
96 DEFINE_WAKE_Q(wakeq); 80 DEFINE_WAKE_Q(wakeq);
97 unsigned long flags; 81 unsigned long flags;
98 bool enabled; 82 bool enabled;
99 83
100 preempt_disable(); 84 preempt_disable();
101 raw_spin_lock_irqsave(&stopper->lock, 85 raw_spin_lock_irqsave(&stopper->lock, flags);
102 enabled = stopper->enabled; 86 enabled = stopper->enabled;
103 if (enabled) 87 if (enabled)
104 __cpu_stop_queue_work(stopper, 88 __cpu_stop_queue_work(stopper, work, &wakeq);
105 else if (work->done) 89 else if (work->done)
106 cpu_stop_signal_done(work->don 90 cpu_stop_signal_done(work->done);
107 raw_spin_unlock_irqrestore(&stopper->l 91 raw_spin_unlock_irqrestore(&stopper->lock, flags);
108 92
109 wake_up_q(&wakeq); 93 wake_up_q(&wakeq);
110 preempt_enable(); 94 preempt_enable();
111 95
112 return enabled; 96 return enabled;
113 } 97 }
114 98
115 /** 99 /**
116 * stop_one_cpu - stop a cpu 100 * stop_one_cpu - stop a cpu
117 * @cpu: cpu to stop 101 * @cpu: cpu to stop
118 * @fn: function to execute 102 * @fn: function to execute
119 * @arg: argument to @fn 103 * @arg: argument to @fn
120 * 104 *
121 * Execute @fn(@arg) on @cpu. @fn is run in a 105 * Execute @fn(@arg) on @cpu. @fn is run in a process context with
122 * the highest priority preempting any task on 106 * the highest priority preempting any task on the cpu and
123 * monopolizing it. This function returns aft 107 * monopolizing it. This function returns after the execution is
124 * complete. 108 * complete.
125 * 109 *
126 * This function doesn't guarantee @cpu stays 110 * This function doesn't guarantee @cpu stays online till @fn
127 * completes. If @cpu goes down in the middle 111 * completes. If @cpu goes down in the middle, execution may happen
128 * partially or fully on different cpus. @fn 112 * partially or fully on different cpus. @fn should either be ready
129 * for that or the caller should ensure that @ 113 * for that or the caller should ensure that @cpu stays online until
130 * this function completes. 114 * this function completes.
131 * 115 *
132 * CONTEXT: 116 * CONTEXT:
133 * Might sleep. 117 * Might sleep.
134 * 118 *
135 * RETURNS: 119 * RETURNS:
136 * -ENOENT if @fn(@arg) was not executed becau 120 * -ENOENT if @fn(@arg) was not executed because @cpu was offline;
137 * otherwise, the return value of @fn. 121 * otherwise, the return value of @fn.
138 */ 122 */
139 int stop_one_cpu(unsigned int cpu, cpu_stop_fn 123 int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg)
140 { 124 {
141 struct cpu_stop_done done; 125 struct cpu_stop_done done;
142 struct cpu_stop_work work = { .fn = fn !! 126 struct cpu_stop_work work = { .fn = fn, .arg = arg, .done = &done };
143 127
144 cpu_stop_init_done(&done, 1); 128 cpu_stop_init_done(&done, 1);
145 if (!cpu_stop_queue_work(cpu, &work)) 129 if (!cpu_stop_queue_work(cpu, &work))
146 return -ENOENT; 130 return -ENOENT;
147 /* 131 /*
148 * In case @cpu == smp_proccessor_id() 132 * In case @cpu == smp_proccessor_id() we can avoid a sleep+wakeup
149 * cycle by doing a preemption: 133 * cycle by doing a preemption:
150 */ 134 */
151 cond_resched(); 135 cond_resched();
152 wait_for_completion(&done.completion); 136 wait_for_completion(&done.completion);
153 return done.ret; 137 return done.ret;
154 } 138 }
155 139
156 /* This controls the threads on each CPU. */ 140 /* This controls the threads on each CPU. */
157 enum multi_stop_state { 141 enum multi_stop_state {
158 /* Dummy starting state for thread. */ 142 /* Dummy starting state for thread. */
159 MULTI_STOP_NONE, 143 MULTI_STOP_NONE,
160 /* Awaiting everyone to be scheduled. 144 /* Awaiting everyone to be scheduled. */
161 MULTI_STOP_PREPARE, 145 MULTI_STOP_PREPARE,
162 /* Disable interrupts. */ 146 /* Disable interrupts. */
163 MULTI_STOP_DISABLE_IRQ, 147 MULTI_STOP_DISABLE_IRQ,
164 /* Run the function */ 148 /* Run the function */
165 MULTI_STOP_RUN, 149 MULTI_STOP_RUN,
166 /* Exit */ 150 /* Exit */
167 MULTI_STOP_EXIT, 151 MULTI_STOP_EXIT,
168 }; 152 };
169 153
170 struct multi_stop_data { 154 struct multi_stop_data {
171 cpu_stop_fn_t fn; 155 cpu_stop_fn_t fn;
172 void *data; 156 void *data;
173 /* Like num_online_cpus(), but hotplug 157 /* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */
174 unsigned int num_threads; 158 unsigned int num_threads;
175 const struct cpumask *active_cpus; 159 const struct cpumask *active_cpus;
176 160
177 enum multi_stop_state state; 161 enum multi_stop_state state;
178 atomic_t thread_ack; 162 atomic_t thread_ack;
179 }; 163 };
180 164
181 static void set_state(struct multi_stop_data * 165 static void set_state(struct multi_stop_data *msdata,
182 enum multi_stop_state ne 166 enum multi_stop_state newstate)
183 { 167 {
184 /* Reset ack counter. */ 168 /* Reset ack counter. */
185 atomic_set(&msdata->thread_ack, msdata 169 atomic_set(&msdata->thread_ack, msdata->num_threads);
186 smp_wmb(); 170 smp_wmb();
187 WRITE_ONCE(msdata->state, newstate); 171 WRITE_ONCE(msdata->state, newstate);
188 } 172 }
189 173
190 /* Last one to ack a state moves to the next s 174 /* Last one to ack a state moves to the next state. */
191 static void ack_state(struct multi_stop_data * 175 static void ack_state(struct multi_stop_data *msdata)
192 { 176 {
193 if (atomic_dec_and_test(&msdata->threa 177 if (atomic_dec_and_test(&msdata->thread_ack))
194 set_state(msdata, msdata->stat 178 set_state(msdata, msdata->state + 1);
195 } 179 }
196 180
197 notrace void __weak stop_machine_yield(const s !! 181 void __weak stop_machine_yield(const struct cpumask *cpumask)
198 { 182 {
199 cpu_relax(); 183 cpu_relax();
200 } 184 }
201 185
202 /* This is the cpu_stop function which stops t 186 /* This is the cpu_stop function which stops the CPU. */
203 static int multi_cpu_stop(void *data) 187 static int multi_cpu_stop(void *data)
204 { 188 {
205 struct multi_stop_data *msdata = data; 189 struct multi_stop_data *msdata = data;
206 enum multi_stop_state newstate, cursta 190 enum multi_stop_state newstate, curstate = MULTI_STOP_NONE;
207 int cpu = smp_processor_id(), err = 0; 191 int cpu = smp_processor_id(), err = 0;
208 const struct cpumask *cpumask; 192 const struct cpumask *cpumask;
209 unsigned long flags; 193 unsigned long flags;
210 bool is_active; 194 bool is_active;
211 195
212 /* 196 /*
213 * When called from stop_machine_from_ 197 * When called from stop_machine_from_inactive_cpu(), irq might
214 * already be disabled. Save the stat 198 * already be disabled. Save the state and restore it on exit.
215 */ 199 */
216 local_save_flags(flags); 200 local_save_flags(flags);
217 201
218 if (!msdata->active_cpus) { 202 if (!msdata->active_cpus) {
219 cpumask = cpu_online_mask; 203 cpumask = cpu_online_mask;
220 is_active = cpu == cpumask_fir 204 is_active = cpu == cpumask_first(cpumask);
221 } else { 205 } else {
222 cpumask = msdata->active_cpus; 206 cpumask = msdata->active_cpus;
223 is_active = cpumask_test_cpu(c 207 is_active = cpumask_test_cpu(cpu, cpumask);
224 } 208 }
225 209
226 /* Simple state machine */ 210 /* Simple state machine */
227 do { 211 do {
228 /* Chill out and ensure we re- 212 /* Chill out and ensure we re-read multi_stop_state. */
229 stop_machine_yield(cpumask); 213 stop_machine_yield(cpumask);
230 newstate = READ_ONCE(msdata->s 214 newstate = READ_ONCE(msdata->state);
231 if (newstate != curstate) { 215 if (newstate != curstate) {
232 curstate = newstate; 216 curstate = newstate;
233 switch (curstate) { 217 switch (curstate) {
234 case MULTI_STOP_DISABL 218 case MULTI_STOP_DISABLE_IRQ:
235 local_irq_disa 219 local_irq_disable();
236 hard_irq_disab 220 hard_irq_disable();
237 break; 221 break;
238 case MULTI_STOP_RUN: 222 case MULTI_STOP_RUN:
239 if (is_active) 223 if (is_active)
240 err = 224 err = msdata->fn(msdata->data);
241 break; 225 break;
242 default: 226 default:
243 break; 227 break;
244 } 228 }
245 ack_state(msdata); 229 ack_state(msdata);
246 } else if (curstate > MULTI_ST 230 } else if (curstate > MULTI_STOP_PREPARE) {
247 /* 231 /*
248 * At this stage all o 232 * At this stage all other CPUs we depend on must spin
249 * in the same loop. A 233 * in the same loop. Any reason for hard-lockup should
250 * be detected and rep 234 * be detected and reported on their side.
251 */ 235 */
252 touch_nmi_watchdog(); 236 touch_nmi_watchdog();
253 } 237 }
254 rcu_momentary_dyntick_idle(); <<
255 } while (curstate != MULTI_STOP_EXIT); 238 } while (curstate != MULTI_STOP_EXIT);
256 239
257 local_irq_restore(flags); 240 local_irq_restore(flags);
258 return err; 241 return err;
259 } 242 }
260 243
261 static int cpu_stop_queue_two_works(int cpu1, 244 static int cpu_stop_queue_two_works(int cpu1, struct cpu_stop_work *work1,
262 int cpu2, 245 int cpu2, struct cpu_stop_work *work2)
263 { 246 {
264 struct cpu_stopper *stopper1 = per_cpu 247 struct cpu_stopper *stopper1 = per_cpu_ptr(&cpu_stopper, cpu1);
265 struct cpu_stopper *stopper2 = per_cpu 248 struct cpu_stopper *stopper2 = per_cpu_ptr(&cpu_stopper, cpu2);
266 DEFINE_WAKE_Q(wakeq); 249 DEFINE_WAKE_Q(wakeq);
267 int err; 250 int err;
268 251
269 retry: 252 retry:
270 /* 253 /*
271 * The waking up of stopper threads ha 254 * The waking up of stopper threads has to happen in the same
272 * scheduling context as the queueing. 255 * scheduling context as the queueing. Otherwise, there is a
273 * possibility of one of the above sto 256 * possibility of one of the above stoppers being woken up by another
274 * CPU, and preempting us. This will c 257 * CPU, and preempting us. This will cause us to not wake up the other
275 * stopper forever. 258 * stopper forever.
276 */ 259 */
277 preempt_disable(); 260 preempt_disable();
278 raw_spin_lock_irq(&stopper1->lock); 261 raw_spin_lock_irq(&stopper1->lock);
279 raw_spin_lock_nested(&stopper2->lock, 262 raw_spin_lock_nested(&stopper2->lock, SINGLE_DEPTH_NESTING);
280 263
281 if (!stopper1->enabled || !stopper2->e 264 if (!stopper1->enabled || !stopper2->enabled) {
282 err = -ENOENT; 265 err = -ENOENT;
283 goto unlock; 266 goto unlock;
284 } 267 }
285 268
286 /* 269 /*
287 * Ensure that if we race with __stop_ 270 * Ensure that if we race with __stop_cpus() the stoppers won't get
288 * queued up in reverse order leading 271 * queued up in reverse order leading to system deadlock.
289 * 272 *
290 * We can't miss stop_cpus_in_progress 273 * We can't miss stop_cpus_in_progress if queue_stop_cpus_work() has
291 * queued a work on cpu1 but not on cp 274 * queued a work on cpu1 but not on cpu2, we hold both locks.
292 * 275 *
293 * It can be falsely true but it is sa 276 * It can be falsely true but it is safe to spin until it is cleared,
294 * queue_stop_cpus_work() does everyth 277 * queue_stop_cpus_work() does everything under preempt_disable().
295 */ 278 */
296 if (unlikely(stop_cpus_in_progress)) { 279 if (unlikely(stop_cpus_in_progress)) {
297 err = -EDEADLK; 280 err = -EDEADLK;
298 goto unlock; 281 goto unlock;
299 } 282 }
300 283
301 err = 0; 284 err = 0;
302 __cpu_stop_queue_work(stopper1, work1, 285 __cpu_stop_queue_work(stopper1, work1, &wakeq);
303 __cpu_stop_queue_work(stopper2, work2, 286 __cpu_stop_queue_work(stopper2, work2, &wakeq);
304 287
305 unlock: 288 unlock:
306 raw_spin_unlock(&stopper2->lock); 289 raw_spin_unlock(&stopper2->lock);
307 raw_spin_unlock_irq(&stopper1->lock); 290 raw_spin_unlock_irq(&stopper1->lock);
308 291
309 if (unlikely(err == -EDEADLK)) { 292 if (unlikely(err == -EDEADLK)) {
310 preempt_enable(); 293 preempt_enable();
311 294
312 while (stop_cpus_in_progress) 295 while (stop_cpus_in_progress)
313 cpu_relax(); 296 cpu_relax();
314 297
315 goto retry; 298 goto retry;
316 } 299 }
317 300
318 wake_up_q(&wakeq); 301 wake_up_q(&wakeq);
319 preempt_enable(); 302 preempt_enable();
320 303
321 return err; 304 return err;
322 } 305 }
323 /** 306 /**
324 * stop_two_cpus - stops two cpus 307 * stop_two_cpus - stops two cpus
325 * @cpu1: the cpu to stop 308 * @cpu1: the cpu to stop
326 * @cpu2: the other cpu to stop 309 * @cpu2: the other cpu to stop
327 * @fn: function to execute 310 * @fn: function to execute
328 * @arg: argument to @fn 311 * @arg: argument to @fn
329 * 312 *
330 * Stops both the current and specified CPU an 313 * Stops both the current and specified CPU and runs @fn on one of them.
331 * 314 *
332 * returns when both are completed. 315 * returns when both are completed.
333 */ 316 */
334 int stop_two_cpus(unsigned int cpu1, unsigned 317 int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *arg)
335 { 318 {
336 struct cpu_stop_done done; 319 struct cpu_stop_done done;
337 struct cpu_stop_work work1, work2; 320 struct cpu_stop_work work1, work2;
338 struct multi_stop_data msdata; 321 struct multi_stop_data msdata;
339 322
340 msdata = (struct multi_stop_data){ 323 msdata = (struct multi_stop_data){
341 .fn = fn, 324 .fn = fn,
342 .data = arg, 325 .data = arg,
343 .num_threads = 2, 326 .num_threads = 2,
344 .active_cpus = cpumask_of(cpu1 327 .active_cpus = cpumask_of(cpu1),
345 }; 328 };
346 329
347 work1 = work2 = (struct cpu_stop_work) 330 work1 = work2 = (struct cpu_stop_work){
348 .fn = multi_cpu_stop, 331 .fn = multi_cpu_stop,
349 .arg = &msdata, 332 .arg = &msdata,
350 .done = &done, !! 333 .done = &done
351 .caller = _RET_IP_, <<
352 }; 334 };
353 335
354 cpu_stop_init_done(&done, 2); 336 cpu_stop_init_done(&done, 2);
355 set_state(&msdata, MULTI_STOP_PREPARE) 337 set_state(&msdata, MULTI_STOP_PREPARE);
356 338
357 if (cpu1 > cpu2) 339 if (cpu1 > cpu2)
358 swap(cpu1, cpu2); 340 swap(cpu1, cpu2);
359 if (cpu_stop_queue_two_works(cpu1, &wo 341 if (cpu_stop_queue_two_works(cpu1, &work1, cpu2, &work2))
360 return -ENOENT; 342 return -ENOENT;
361 343
362 wait_for_completion(&done.completion); 344 wait_for_completion(&done.completion);
363 return done.ret; 345 return done.ret;
364 } 346 }
365 347
366 /** 348 /**
367 * stop_one_cpu_nowait - stop a cpu but don't 349 * stop_one_cpu_nowait - stop a cpu but don't wait for completion
368 * @cpu: cpu to stop 350 * @cpu: cpu to stop
369 * @fn: function to execute 351 * @fn: function to execute
370 * @arg: argument to @fn 352 * @arg: argument to @fn
371 * @work_buf: pointer to cpu_stop_work structu 353 * @work_buf: pointer to cpu_stop_work structure
372 * 354 *
373 * Similar to stop_one_cpu() but doesn't wait 355 * Similar to stop_one_cpu() but doesn't wait for completion. The
374 * caller is responsible for ensuring @work_bu 356 * caller is responsible for ensuring @work_buf is currently unused
375 * and will remain untouched until stopper sta 357 * and will remain untouched until stopper starts executing @fn.
376 * 358 *
377 * CONTEXT: 359 * CONTEXT:
378 * Don't care. 360 * Don't care.
379 * 361 *
380 * RETURNS: 362 * RETURNS:
381 * true if cpu_stop_work was queued successful 363 * true if cpu_stop_work was queued successfully and @fn will be called,
382 * false otherwise. 364 * false otherwise.
383 */ 365 */
384 bool stop_one_cpu_nowait(unsigned int cpu, cpu 366 bool stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
385 struct cpu_stop_work * 367 struct cpu_stop_work *work_buf)
386 { 368 {
387 *work_buf = (struct cpu_stop_work){ .f !! 369 *work_buf = (struct cpu_stop_work){ .fn = fn, .arg = arg, };
388 return cpu_stop_queue_work(cpu, work_b 370 return cpu_stop_queue_work(cpu, work_buf);
389 } 371 }
390 372
391 static bool queue_stop_cpus_work(const struct 373 static bool queue_stop_cpus_work(const struct cpumask *cpumask,
392 cpu_stop_fn_t 374 cpu_stop_fn_t fn, void *arg,
393 struct cpu_st 375 struct cpu_stop_done *done)
394 { 376 {
395 struct cpu_stop_work *work; 377 struct cpu_stop_work *work;
396 unsigned int cpu; 378 unsigned int cpu;
397 bool queued = false; 379 bool queued = false;
398 380
399 /* 381 /*
400 * Disable preemption while queueing t 382 * Disable preemption while queueing to avoid getting
401 * preempted by a stopper which might 383 * preempted by a stopper which might wait for other stoppers
402 * to enter @fn which can lead to dead 384 * to enter @fn which can lead to deadlock.
403 */ 385 */
404 preempt_disable(); 386 preempt_disable();
405 stop_cpus_in_progress = true; 387 stop_cpus_in_progress = true;
406 barrier(); 388 barrier();
407 for_each_cpu(cpu, cpumask) { 389 for_each_cpu(cpu, cpumask) {
408 work = &per_cpu(cpu_stopper.st 390 work = &per_cpu(cpu_stopper.stop_work, cpu);
409 work->fn = fn; 391 work->fn = fn;
410 work->arg = arg; 392 work->arg = arg;
411 work->done = done; 393 work->done = done;
412 work->caller = _RET_IP_; <<
413 if (cpu_stop_queue_work(cpu, w 394 if (cpu_stop_queue_work(cpu, work))
414 queued = true; 395 queued = true;
415 } 396 }
416 barrier(); 397 barrier();
417 stop_cpus_in_progress = false; 398 stop_cpus_in_progress = false;
418 preempt_enable(); 399 preempt_enable();
419 400
420 return queued; 401 return queued;
421 } 402 }
422 403
423 static int __stop_cpus(const struct cpumask *c 404 static int __stop_cpus(const struct cpumask *cpumask,
424 cpu_stop_fn_t fn, void 405 cpu_stop_fn_t fn, void *arg)
425 { 406 {
426 struct cpu_stop_done done; 407 struct cpu_stop_done done;
427 408
428 cpu_stop_init_done(&done, cpumask_weig 409 cpu_stop_init_done(&done, cpumask_weight(cpumask));
429 if (!queue_stop_cpus_work(cpumask, fn, 410 if (!queue_stop_cpus_work(cpumask, fn, arg, &done))
430 return -ENOENT; 411 return -ENOENT;
431 wait_for_completion(&done.completion); 412 wait_for_completion(&done.completion);
432 return done.ret; 413 return done.ret;
433 } 414 }
434 415
435 /** 416 /**
436 * stop_cpus - stop multiple cpus 417 * stop_cpus - stop multiple cpus
437 * @cpumask: cpus to stop 418 * @cpumask: cpus to stop
438 * @fn: function to execute 419 * @fn: function to execute
439 * @arg: argument to @fn 420 * @arg: argument to @fn
440 * 421 *
441 * Execute @fn(@arg) on online cpus in @cpumas 422 * Execute @fn(@arg) on online cpus in @cpumask. On each target cpu,
442 * @fn is run in a process context with the hi 423 * @fn is run in a process context with the highest priority
443 * preempting any task on the cpu and monopoli 424 * preempting any task on the cpu and monopolizing it. This function
444 * returns after all executions are complete. 425 * returns after all executions are complete.
445 * 426 *
446 * This function doesn't guarantee the cpus in 427 * This function doesn't guarantee the cpus in @cpumask stay online
447 * till @fn completes. If some cpus go down i 428 * till @fn completes. If some cpus go down in the middle, execution
448 * on the cpu may happen partially or fully on 429 * on the cpu may happen partially or fully on different cpus. @fn
449 * should either be ready for that or the call 430 * should either be ready for that or the caller should ensure that
450 * the cpus stay online until this function co 431 * the cpus stay online until this function completes.
451 * 432 *
452 * All stop_cpus() calls are serialized making 433 * All stop_cpus() calls are serialized making it safe for @fn to wait
453 * for all cpus to start executing it. 434 * for all cpus to start executing it.
454 * 435 *
455 * CONTEXT: 436 * CONTEXT:
456 * Might sleep. 437 * Might sleep.
457 * 438 *
458 * RETURNS: 439 * RETURNS:
459 * -ENOENT if @fn(@arg) was not executed at al 440 * -ENOENT if @fn(@arg) was not executed at all because all cpus in
460 * @cpumask were offline; otherwise, 0 if all 441 * @cpumask were offline; otherwise, 0 if all executions of @fn
461 * returned 0, any non zero return value if an 442 * returned 0, any non zero return value if any returned non zero.
462 */ 443 */
463 static int stop_cpus(const struct cpumask *cpu !! 444 int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
464 { 445 {
465 int ret; 446 int ret;
466 447
467 /* static works are used, process one 448 /* static works are used, process one request at a time */
468 mutex_lock(&stop_cpus_mutex); 449 mutex_lock(&stop_cpus_mutex);
469 ret = __stop_cpus(cpumask, fn, arg); 450 ret = __stop_cpus(cpumask, fn, arg);
470 mutex_unlock(&stop_cpus_mutex); 451 mutex_unlock(&stop_cpus_mutex);
471 return ret; 452 return ret;
472 } 453 }
473 454
>> 455 /**
>> 456 * try_stop_cpus - try to stop multiple cpus
>> 457 * @cpumask: cpus to stop
>> 458 * @fn: function to execute
>> 459 * @arg: argument to @fn
>> 460 *
>> 461 * Identical to stop_cpus() except that it fails with -EAGAIN if
>> 462 * someone else is already using the facility.
>> 463 *
>> 464 * CONTEXT:
>> 465 * Might sleep.
>> 466 *
>> 467 * RETURNS:
>> 468 * -EAGAIN if someone else is already stopping cpus, -ENOENT if
>> 469 * @fn(@arg) was not executed at all because all cpus in @cpumask were
>> 470 * offline; otherwise, 0 if all executions of @fn returned 0, any non
>> 471 * zero return value if any returned non zero.
>> 472 */
>> 473 int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
>> 474 {
>> 475 int ret;
>> 476
>> 477 /* static works are used, process one request at a time */
>> 478 if (!mutex_trylock(&stop_cpus_mutex))
>> 479 return -EAGAIN;
>> 480 ret = __stop_cpus(cpumask, fn, arg);
>> 481 mutex_unlock(&stop_cpus_mutex);
>> 482 return ret;
>> 483 }
>> 484
474 static int cpu_stop_should_run(unsigned int cp 485 static int cpu_stop_should_run(unsigned int cpu)
475 { 486 {
476 struct cpu_stopper *stopper = &per_cpu 487 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
477 unsigned long flags; 488 unsigned long flags;
478 int run; 489 int run;
479 490
480 raw_spin_lock_irqsave(&stopper->lock, 491 raw_spin_lock_irqsave(&stopper->lock, flags);
481 run = !list_empty(&stopper->works); 492 run = !list_empty(&stopper->works);
482 raw_spin_unlock_irqrestore(&stopper->l 493 raw_spin_unlock_irqrestore(&stopper->lock, flags);
483 return run; 494 return run;
484 } 495 }
485 496
486 static void cpu_stopper_thread(unsigned int cp 497 static void cpu_stopper_thread(unsigned int cpu)
487 { 498 {
488 struct cpu_stopper *stopper = &per_cpu 499 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
489 struct cpu_stop_work *work; 500 struct cpu_stop_work *work;
490 501
491 repeat: 502 repeat:
492 work = NULL; 503 work = NULL;
493 raw_spin_lock_irq(&stopper->lock); 504 raw_spin_lock_irq(&stopper->lock);
494 if (!list_empty(&stopper->works)) { 505 if (!list_empty(&stopper->works)) {
495 work = list_first_entry(&stopp 506 work = list_first_entry(&stopper->works,
496 struct 507 struct cpu_stop_work, list);
497 list_del_init(&work->list); 508 list_del_init(&work->list);
498 } 509 }
499 raw_spin_unlock_irq(&stopper->lock); 510 raw_spin_unlock_irq(&stopper->lock);
500 511
501 if (work) { 512 if (work) {
502 cpu_stop_fn_t fn = work->fn; 513 cpu_stop_fn_t fn = work->fn;
503 void *arg = work->arg; 514 void *arg = work->arg;
504 struct cpu_stop_done *done = w 515 struct cpu_stop_done *done = work->done;
505 int ret; 516 int ret;
506 517
507 /* cpu stop callbacks must not 518 /* cpu stop callbacks must not sleep, make in_atomic() == T */
508 stopper->caller = work->caller <<
509 stopper->fn = fn; <<
510 preempt_count_inc(); 519 preempt_count_inc();
511 ret = fn(arg); 520 ret = fn(arg);
512 if (done) { 521 if (done) {
513 if (ret) 522 if (ret)
514 done->ret = re 523 done->ret = ret;
515 cpu_stop_signal_done(d 524 cpu_stop_signal_done(done);
516 } 525 }
517 preempt_count_dec(); 526 preempt_count_dec();
518 stopper->fn = NULL; <<
519 stopper->caller = 0; <<
520 WARN_ONCE(preempt_count(), 527 WARN_ONCE(preempt_count(),
521 "cpu_stop: %ps(%p) l 528 "cpu_stop: %ps(%p) leaked preempt count\n", fn, arg);
522 goto repeat; 529 goto repeat;
523 } 530 }
524 } 531 }
525 532
526 void stop_machine_park(int cpu) 533 void stop_machine_park(int cpu)
527 { 534 {
528 struct cpu_stopper *stopper = &per_cpu 535 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
529 /* 536 /*
530 * Lockless. cpu_stopper_thread() will 537 * Lockless. cpu_stopper_thread() will take stopper->lock and flush
531 * the pending works before it parks, 538 * the pending works before it parks, until then it is fine to queue
532 * the new works. 539 * the new works.
533 */ 540 */
534 stopper->enabled = false; 541 stopper->enabled = false;
535 kthread_park(stopper->thread); 542 kthread_park(stopper->thread);
536 } 543 }
537 544
>> 545 extern void sched_set_stop_task(int cpu, struct task_struct *stop);
>> 546
538 static void cpu_stop_create(unsigned int cpu) 547 static void cpu_stop_create(unsigned int cpu)
539 { 548 {
540 sched_set_stop_task(cpu, per_cpu(cpu_s 549 sched_set_stop_task(cpu, per_cpu(cpu_stopper.thread, cpu));
541 } 550 }
542 551
543 static void cpu_stop_park(unsigned int cpu) 552 static void cpu_stop_park(unsigned int cpu)
544 { 553 {
545 struct cpu_stopper *stopper = &per_cpu 554 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
546 555
547 WARN_ON(!list_empty(&stopper->works)); 556 WARN_ON(!list_empty(&stopper->works));
548 } 557 }
549 558
550 void stop_machine_unpark(int cpu) 559 void stop_machine_unpark(int cpu)
551 { 560 {
552 struct cpu_stopper *stopper = &per_cpu 561 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
553 562
554 stopper->enabled = true; 563 stopper->enabled = true;
555 kthread_unpark(stopper->thread); 564 kthread_unpark(stopper->thread);
556 } 565 }
557 566
558 static struct smp_hotplug_thread cpu_stop_thre 567 static struct smp_hotplug_thread cpu_stop_threads = {
559 .store = &cpu_stopper 568 .store = &cpu_stopper.thread,
560 .thread_should_run = cpu_stop_sho 569 .thread_should_run = cpu_stop_should_run,
561 .thread_fn = cpu_stopper_ 570 .thread_fn = cpu_stopper_thread,
562 .thread_comm = "migration/% 571 .thread_comm = "migration/%u",
563 .create = cpu_stop_cre 572 .create = cpu_stop_create,
564 .park = cpu_stop_par 573 .park = cpu_stop_park,
565 .selfparking = true, 574 .selfparking = true,
566 }; 575 };
567 576
568 static int __init cpu_stop_init(void) 577 static int __init cpu_stop_init(void)
569 { 578 {
570 unsigned int cpu; 579 unsigned int cpu;
571 580
572 for_each_possible_cpu(cpu) { 581 for_each_possible_cpu(cpu) {
573 struct cpu_stopper *stopper = 582 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
574 583
575 raw_spin_lock_init(&stopper->l 584 raw_spin_lock_init(&stopper->lock);
576 INIT_LIST_HEAD(&stopper->works 585 INIT_LIST_HEAD(&stopper->works);
577 } 586 }
578 587
579 BUG_ON(smpboot_register_percpu_thread( 588 BUG_ON(smpboot_register_percpu_thread(&cpu_stop_threads));
580 stop_machine_unpark(raw_smp_processor_ 589 stop_machine_unpark(raw_smp_processor_id());
581 stop_machine_initialized = true; 590 stop_machine_initialized = true;
582 return 0; 591 return 0;
583 } 592 }
584 early_initcall(cpu_stop_init); 593 early_initcall(cpu_stop_init);
585 594
586 int stop_machine_cpuslocked(cpu_stop_fn_t fn, 595 int stop_machine_cpuslocked(cpu_stop_fn_t fn, void *data,
587 const struct cpuma 596 const struct cpumask *cpus)
588 { 597 {
589 struct multi_stop_data msdata = { 598 struct multi_stop_data msdata = {
590 .fn = fn, 599 .fn = fn,
591 .data = data, 600 .data = data,
592 .num_threads = num_online_cpus 601 .num_threads = num_online_cpus(),
593 .active_cpus = cpus, 602 .active_cpus = cpus,
594 }; 603 };
595 604
596 lockdep_assert_cpus_held(); 605 lockdep_assert_cpus_held();
597 606
598 if (!stop_machine_initialized) { 607 if (!stop_machine_initialized) {
599 /* 608 /*
600 * Handle the case where stop_ 609 * Handle the case where stop_machine() is called
601 * early in boot before stop_m 610 * early in boot before stop_machine() has been
602 * initialized. 611 * initialized.
603 */ 612 */
604 unsigned long flags; 613 unsigned long flags;
605 int ret; 614 int ret;
606 615
607 WARN_ON_ONCE(msdata.num_thread 616 WARN_ON_ONCE(msdata.num_threads != 1);
608 617
609 local_irq_save(flags); 618 local_irq_save(flags);
610 hard_irq_disable(); 619 hard_irq_disable();
611 ret = (*fn)(data); 620 ret = (*fn)(data);
612 local_irq_restore(flags); 621 local_irq_restore(flags);
613 622
614 return ret; 623 return ret;
615 } 624 }
616 625
617 /* Set the initial state and stop all 626 /* Set the initial state and stop all online cpus. */
618 set_state(&msdata, MULTI_STOP_PREPARE) 627 set_state(&msdata, MULTI_STOP_PREPARE);
619 return stop_cpus(cpu_online_mask, mult 628 return stop_cpus(cpu_online_mask, multi_cpu_stop, &msdata);
620 } 629 }
621 630
622 int stop_machine(cpu_stop_fn_t fn, void *data, 631 int stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)
623 { 632 {
624 int ret; 633 int ret;
625 634
626 /* No CPUs can come up or down during 635 /* No CPUs can come up or down during this. */
627 cpus_read_lock(); 636 cpus_read_lock();
628 ret = stop_machine_cpuslocked(fn, data 637 ret = stop_machine_cpuslocked(fn, data, cpus);
629 cpus_read_unlock(); 638 cpus_read_unlock();
630 return ret; 639 return ret;
631 } 640 }
632 EXPORT_SYMBOL_GPL(stop_machine); 641 EXPORT_SYMBOL_GPL(stop_machine);
633 <<
634 #ifdef CONFIG_SCHED_SMT <<
635 int stop_core_cpuslocked(unsigned int cpu, cpu <<
636 { <<
637 const struct cpumask *smt_mask = cpu_s <<
638 <<
639 struct multi_stop_data msdata = { <<
640 .fn = fn, <<
641 .data = data, <<
642 .num_threads = cpumask_weight( <<
643 .active_cpus = smt_mask, <<
644 }; <<
645 <<
646 lockdep_assert_cpus_held(); <<
647 <<
648 /* Set the initial state and stop all <<
649 set_state(&msdata, MULTI_STOP_PREPARE) <<
650 return stop_cpus(smt_mask, multi_cpu_s <<
651 } <<
652 EXPORT_SYMBOL_GPL(stop_core_cpuslocked); <<
653 #endif <<
654 642
655 /** 643 /**
656 * stop_machine_from_inactive_cpu - stop_machi 644 * stop_machine_from_inactive_cpu - stop_machine() from inactive CPU
657 * @fn: the function to run 645 * @fn: the function to run
658 * @data: the data ptr for the @fn() 646 * @data: the data ptr for the @fn()
659 * @cpus: the cpus to run the @fn() on (NULL = 647 * @cpus: the cpus to run the @fn() on (NULL = any online cpu)
660 * 648 *
661 * This is identical to stop_machine() but can 649 * This is identical to stop_machine() but can be called from a CPU which
662 * is not active. The local CPU is in the pro 650 * is not active. The local CPU is in the process of hotplug (so no other
663 * CPU hotplug can start) and not marked activ 651 * CPU hotplug can start) and not marked active and doesn't have enough
664 * context to sleep. 652 * context to sleep.
665 * 653 *
666 * This function provides stop_machine() funct 654 * This function provides stop_machine() functionality for such state by
667 * using busy-wait for synchronization and exe 655 * using busy-wait for synchronization and executing @fn directly for local
668 * CPU. 656 * CPU.
669 * 657 *
670 * CONTEXT: 658 * CONTEXT:
671 * Local CPU is inactive. Temporarily stops a 659 * Local CPU is inactive. Temporarily stops all active CPUs.
672 * 660 *
673 * RETURNS: 661 * RETURNS:
674 * 0 if all executions of @fn returned 0, any 662 * 0 if all executions of @fn returned 0, any non zero return value if any
675 * returned non zero. 663 * returned non zero.
676 */ 664 */
677 int stop_machine_from_inactive_cpu(cpu_stop_fn 665 int stop_machine_from_inactive_cpu(cpu_stop_fn_t fn, void *data,
678 const struct 666 const struct cpumask *cpus)
679 { 667 {
680 struct multi_stop_data msdata = { .fn 668 struct multi_stop_data msdata = { .fn = fn, .data = data,
681 .a 669 .active_cpus = cpus };
682 struct cpu_stop_done done; 670 struct cpu_stop_done done;
683 int ret; 671 int ret;
684 672
685 /* Local CPU must be inactive and CPU 673 /* Local CPU must be inactive and CPU hotplug in progress. */
686 BUG_ON(cpu_active(raw_smp_processor_id 674 BUG_ON(cpu_active(raw_smp_processor_id()));
687 msdata.num_threads = num_active_cpus() 675 msdata.num_threads = num_active_cpus() + 1; /* +1 for local */
688 676
689 /* No proper task established and can' 677 /* No proper task established and can't sleep - busy wait for lock. */
690 while (!mutex_trylock(&stop_cpus_mutex 678 while (!mutex_trylock(&stop_cpus_mutex))
691 cpu_relax(); 679 cpu_relax();
692 680
693 /* Schedule work on other CPUs and exe 681 /* Schedule work on other CPUs and execute directly for local CPU */
694 set_state(&msdata, MULTI_STOP_PREPARE) 682 set_state(&msdata, MULTI_STOP_PREPARE);
695 cpu_stop_init_done(&done, num_active_c 683 cpu_stop_init_done(&done, num_active_cpus());
696 queue_stop_cpus_work(cpu_active_mask, 684 queue_stop_cpus_work(cpu_active_mask, multi_cpu_stop, &msdata,
697 &done); 685 &done);
698 ret = multi_cpu_stop(&msdata); 686 ret = multi_cpu_stop(&msdata);
699 687
700 /* Busy wait for completion. */ 688 /* Busy wait for completion. */
701 while (!completion_done(&done.completi 689 while (!completion_done(&done.completion))
702 cpu_relax(); 690 cpu_relax();
703 691
704 mutex_unlock(&stop_cpus_mutex); 692 mutex_unlock(&stop_cpus_mutex);
705 return ret ?: done.ret; 693 return ret ?: done.ret;
706 } 694 }
707 695
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