1 // SPDX-License-Identifier: GPL-2.0-or-later <<
2 /* 1 /*
3 * kernel/stop_machine.c 2 * kernel/stop_machine.c
4 * 3 *
5 * Copyright (C) 2008, 2005 IBM Corporatio 4 * Copyright (C) 2008, 2005 IBM Corporation.
6 * Copyright (C) 2008, 2005 Rusty Russell 5 * Copyright (C) 2008, 2005 Rusty Russell rusty@rustcorp.com.au
7 * Copyright (C) 2010 SUSE Linux Pro 6 * Copyright (C) 2010 SUSE Linux Products GmbH
8 * Copyright (C) 2010 Tejun Heo <tj@ 7 * Copyright (C) 2010 Tejun Heo <tj@kernel.org>
>> 8 *
>> 9 * This file is released under the GPLv2 and any later version.
9 */ 10 */
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> <<
25 24
26 /* 25 /*
27 * Structure to determine completion condition 26 * Structure to determine completion condition and record errors. May
28 * be shared by works on different cpus. 27 * be shared by works on different cpus.
29 */ 28 */
30 struct cpu_stop_done { 29 struct cpu_stop_done {
31 atomic_t nr_todo; 30 atomic_t nr_todo; /* nr left to execute */
32 int ret; 31 int ret; /* collected return value */
33 struct completion completion; 32 struct completion completion; /* fired if nr_todo reaches 0 */
34 }; 33 };
35 34
36 /* the actual stopper, one per every possible 35 /* the actual stopper, one per every possible cpu, enabled on online cpus */
37 struct cpu_stopper { 36 struct cpu_stopper {
38 struct task_struct *thread; 37 struct task_struct *thread;
39 38
40 raw_spinlock_t lock; !! 39 spinlock_t lock;
41 bool enabled; 40 bool enabled; /* is this stopper enabled? */
42 struct list_head works; 41 struct list_head works; /* list of pending works */
43 42
44 struct cpu_stop_work stop_work; 43 struct cpu_stop_work stop_work; /* for stop_cpus */
45 unsigned long caller; <<
46 cpu_stop_fn_t fn; <<
47 }; 44 };
48 45
49 static DEFINE_PER_CPU(struct cpu_stopper, cpu_ 46 static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper);
50 static bool stop_machine_initialized = false; 47 static bool stop_machine_initialized = false;
51 48
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 */ 49 /* static data for stop_cpus */
67 static DEFINE_MUTEX(stop_cpus_mutex); 50 static DEFINE_MUTEX(stop_cpus_mutex);
68 static bool stop_cpus_in_progress; 51 static bool stop_cpus_in_progress;
69 52
70 static void cpu_stop_init_done(struct cpu_stop 53 static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo)
71 { 54 {
72 memset(done, 0, sizeof(*done)); 55 memset(done, 0, sizeof(*done));
73 atomic_set(&done->nr_todo, nr_todo); 56 atomic_set(&done->nr_todo, nr_todo);
74 init_completion(&done->completion); 57 init_completion(&done->completion);
75 } 58 }
76 59
77 /* signal completion unless @done is NULL */ 60 /* signal completion unless @done is NULL */
78 static void cpu_stop_signal_done(struct cpu_st 61 static void cpu_stop_signal_done(struct cpu_stop_done *done)
79 { 62 {
80 if (atomic_dec_and_test(&done->nr_todo 63 if (atomic_dec_and_test(&done->nr_todo))
81 complete(&done->completion); 64 complete(&done->completion);
82 } 65 }
83 66
84 static void __cpu_stop_queue_work(struct cpu_s 67 static void __cpu_stop_queue_work(struct cpu_stopper *stopper,
85 struct !! 68 struct cpu_stop_work *work)
86 struct <<
87 { 69 {
88 list_add_tail(&work->list, &stopper->w 70 list_add_tail(&work->list, &stopper->works);
89 wake_q_add(wakeq, stopper->thread); !! 71 wake_up_process(stopper->thread);
90 } 72 }
91 73
92 /* queue @work to @stopper. if offline, @work 74 /* queue @work to @stopper. if offline, @work is completed immediately */
93 static bool cpu_stop_queue_work(unsigned int c 75 static bool cpu_stop_queue_work(unsigned int cpu, struct cpu_stop_work *work)
94 { 76 {
95 struct cpu_stopper *stopper = &per_cpu 77 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
96 DEFINE_WAKE_Q(wakeq); <<
97 unsigned long flags; 78 unsigned long flags;
98 bool enabled; 79 bool enabled;
99 80
100 preempt_disable(); !! 81 spin_lock_irqsave(&stopper->lock, flags);
101 raw_spin_lock_irqsave(&stopper->lock, <<
102 enabled = stopper->enabled; 82 enabled = stopper->enabled;
103 if (enabled) 83 if (enabled)
104 __cpu_stop_queue_work(stopper, !! 84 __cpu_stop_queue_work(stopper, work);
105 else if (work->done) 85 else if (work->done)
106 cpu_stop_signal_done(work->don 86 cpu_stop_signal_done(work->done);
107 raw_spin_unlock_irqrestore(&stopper->l !! 87 spin_unlock_irqrestore(&stopper->lock, flags);
108 <<
109 wake_up_q(&wakeq); <<
110 preempt_enable(); <<
111 88
112 return enabled; 89 return enabled;
113 } 90 }
114 91
115 /** 92 /**
116 * stop_one_cpu - stop a cpu 93 * stop_one_cpu - stop a cpu
117 * @cpu: cpu to stop 94 * @cpu: cpu to stop
118 * @fn: function to execute 95 * @fn: function to execute
119 * @arg: argument to @fn 96 * @arg: argument to @fn
120 * 97 *
121 * Execute @fn(@arg) on @cpu. @fn is run in a 98 * Execute @fn(@arg) on @cpu. @fn is run in a process context with
122 * the highest priority preempting any task on 99 * the highest priority preempting any task on the cpu and
123 * monopolizing it. This function returns aft 100 * monopolizing it. This function returns after the execution is
124 * complete. 101 * complete.
125 * 102 *
126 * This function doesn't guarantee @cpu stays 103 * This function doesn't guarantee @cpu stays online till @fn
127 * completes. If @cpu goes down in the middle 104 * completes. If @cpu goes down in the middle, execution may happen
128 * partially or fully on different cpus. @fn 105 * partially or fully on different cpus. @fn should either be ready
129 * for that or the caller should ensure that @ 106 * for that or the caller should ensure that @cpu stays online until
130 * this function completes. 107 * this function completes.
131 * 108 *
132 * CONTEXT: 109 * CONTEXT:
133 * Might sleep. 110 * Might sleep.
134 * 111 *
135 * RETURNS: 112 * RETURNS:
136 * -ENOENT if @fn(@arg) was not executed becau 113 * -ENOENT if @fn(@arg) was not executed because @cpu was offline;
137 * otherwise, the return value of @fn. 114 * otherwise, the return value of @fn.
138 */ 115 */
139 int stop_one_cpu(unsigned int cpu, cpu_stop_fn 116 int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg)
140 { 117 {
141 struct cpu_stop_done done; 118 struct cpu_stop_done done;
142 struct cpu_stop_work work = { .fn = fn !! 119 struct cpu_stop_work work = { .fn = fn, .arg = arg, .done = &done };
143 120
144 cpu_stop_init_done(&done, 1); 121 cpu_stop_init_done(&done, 1);
145 if (!cpu_stop_queue_work(cpu, &work)) 122 if (!cpu_stop_queue_work(cpu, &work))
146 return -ENOENT; 123 return -ENOENT;
147 /* 124 /*
148 * In case @cpu == smp_proccessor_id() 125 * In case @cpu == smp_proccessor_id() we can avoid a sleep+wakeup
149 * cycle by doing a preemption: 126 * cycle by doing a preemption:
150 */ 127 */
151 cond_resched(); 128 cond_resched();
152 wait_for_completion(&done.completion); 129 wait_for_completion(&done.completion);
153 return done.ret; 130 return done.ret;
154 } 131 }
155 132
156 /* This controls the threads on each CPU. */ 133 /* This controls the threads on each CPU. */
157 enum multi_stop_state { 134 enum multi_stop_state {
158 /* Dummy starting state for thread. */ 135 /* Dummy starting state for thread. */
159 MULTI_STOP_NONE, 136 MULTI_STOP_NONE,
160 /* Awaiting everyone to be scheduled. 137 /* Awaiting everyone to be scheduled. */
161 MULTI_STOP_PREPARE, 138 MULTI_STOP_PREPARE,
162 /* Disable interrupts. */ 139 /* Disable interrupts. */
163 MULTI_STOP_DISABLE_IRQ, 140 MULTI_STOP_DISABLE_IRQ,
164 /* Run the function */ 141 /* Run the function */
165 MULTI_STOP_RUN, 142 MULTI_STOP_RUN,
166 /* Exit */ 143 /* Exit */
167 MULTI_STOP_EXIT, 144 MULTI_STOP_EXIT,
168 }; 145 };
169 146
170 struct multi_stop_data { 147 struct multi_stop_data {
171 cpu_stop_fn_t fn; 148 cpu_stop_fn_t fn;
172 void *data; 149 void *data;
173 /* Like num_online_cpus(), but hotplug 150 /* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */
174 unsigned int num_threads; 151 unsigned int num_threads;
175 const struct cpumask *active_cpus; 152 const struct cpumask *active_cpus;
176 153
177 enum multi_stop_state state; 154 enum multi_stop_state state;
178 atomic_t thread_ack; 155 atomic_t thread_ack;
179 }; 156 };
180 157
181 static void set_state(struct multi_stop_data * 158 static void set_state(struct multi_stop_data *msdata,
182 enum multi_stop_state ne 159 enum multi_stop_state newstate)
183 { 160 {
184 /* Reset ack counter. */ 161 /* Reset ack counter. */
185 atomic_set(&msdata->thread_ack, msdata 162 atomic_set(&msdata->thread_ack, msdata->num_threads);
186 smp_wmb(); 163 smp_wmb();
187 WRITE_ONCE(msdata->state, newstate); !! 164 msdata->state = newstate;
188 } 165 }
189 166
190 /* Last one to ack a state moves to the next s 167 /* Last one to ack a state moves to the next state. */
191 static void ack_state(struct multi_stop_data * 168 static void ack_state(struct multi_stop_data *msdata)
192 { 169 {
193 if (atomic_dec_and_test(&msdata->threa 170 if (atomic_dec_and_test(&msdata->thread_ack))
194 set_state(msdata, msdata->stat 171 set_state(msdata, msdata->state + 1);
195 } 172 }
196 173
197 notrace void __weak stop_machine_yield(const s <<
198 { <<
199 cpu_relax(); <<
200 } <<
201 <<
202 /* This is the cpu_stop function which stops t 174 /* This is the cpu_stop function which stops the CPU. */
203 static int multi_cpu_stop(void *data) 175 static int multi_cpu_stop(void *data)
204 { 176 {
205 struct multi_stop_data *msdata = data; 177 struct multi_stop_data *msdata = data;
206 enum multi_stop_state newstate, cursta !! 178 enum multi_stop_state curstate = MULTI_STOP_NONE;
207 int cpu = smp_processor_id(), err = 0; 179 int cpu = smp_processor_id(), err = 0;
208 const struct cpumask *cpumask; <<
209 unsigned long flags; 180 unsigned long flags;
210 bool is_active; 181 bool is_active;
211 182
212 /* 183 /*
213 * When called from stop_machine_from_ 184 * When called from stop_machine_from_inactive_cpu(), irq might
214 * already be disabled. Save the stat 185 * already be disabled. Save the state and restore it on exit.
215 */ 186 */
216 local_save_flags(flags); 187 local_save_flags(flags);
217 188
218 if (!msdata->active_cpus) { !! 189 if (!msdata->active_cpus)
219 cpumask = cpu_online_mask; !! 190 is_active = cpu == cpumask_first(cpu_online_mask);
220 is_active = cpu == cpumask_fir !! 191 else
221 } else { !! 192 is_active = cpumask_test_cpu(cpu, msdata->active_cpus);
222 cpumask = msdata->active_cpus; <<
223 is_active = cpumask_test_cpu(c <<
224 } <<
225 193
226 /* Simple state machine */ 194 /* Simple state machine */
227 do { 195 do {
228 /* Chill out and ensure we re- 196 /* Chill out and ensure we re-read multi_stop_state. */
229 stop_machine_yield(cpumask); !! 197 cpu_relax_yield();
230 newstate = READ_ONCE(msdata->s !! 198 if (msdata->state != curstate) {
231 if (newstate != curstate) { !! 199 curstate = msdata->state;
232 curstate = newstate; <<
233 switch (curstate) { 200 switch (curstate) {
234 case MULTI_STOP_DISABL 201 case MULTI_STOP_DISABLE_IRQ:
235 local_irq_disa 202 local_irq_disable();
236 hard_irq_disab 203 hard_irq_disable();
237 break; 204 break;
238 case MULTI_STOP_RUN: 205 case MULTI_STOP_RUN:
239 if (is_active) 206 if (is_active)
240 err = 207 err = msdata->fn(msdata->data);
241 break; 208 break;
242 default: 209 default:
243 break; 210 break;
244 } 211 }
245 ack_state(msdata); 212 ack_state(msdata);
246 } else if (curstate > MULTI_ST 213 } else if (curstate > MULTI_STOP_PREPARE) {
247 /* 214 /*
248 * At this stage all o 215 * At this stage all other CPUs we depend on must spin
249 * in the same loop. A 216 * in the same loop. Any reason for hard-lockup should
250 * be detected and rep 217 * be detected and reported on their side.
251 */ 218 */
252 touch_nmi_watchdog(); 219 touch_nmi_watchdog();
253 } 220 }
254 rcu_momentary_dyntick_idle(); <<
255 } while (curstate != MULTI_STOP_EXIT); 221 } while (curstate != MULTI_STOP_EXIT);
256 222
257 local_irq_restore(flags); 223 local_irq_restore(flags);
258 return err; 224 return err;
259 } 225 }
260 226
261 static int cpu_stop_queue_two_works(int cpu1, 227 static int cpu_stop_queue_two_works(int cpu1, struct cpu_stop_work *work1,
262 int cpu2, 228 int cpu2, struct cpu_stop_work *work2)
263 { 229 {
264 struct cpu_stopper *stopper1 = per_cpu 230 struct cpu_stopper *stopper1 = per_cpu_ptr(&cpu_stopper, cpu1);
265 struct cpu_stopper *stopper2 = per_cpu 231 struct cpu_stopper *stopper2 = per_cpu_ptr(&cpu_stopper, cpu2);
266 DEFINE_WAKE_Q(wakeq); <<
267 int err; 232 int err;
268 <<
269 retry: 233 retry:
270 /* !! 234 spin_lock_irq(&stopper1->lock);
271 * The waking up of stopper threads ha !! 235 spin_lock_nested(&stopper2->lock, SINGLE_DEPTH_NESTING);
272 * scheduling context as the queueing. <<
273 * possibility of one of the above sto <<
274 * CPU, and preempting us. This will c <<
275 * stopper forever. <<
276 */ <<
277 preempt_disable(); <<
278 raw_spin_lock_irq(&stopper1->lock); <<
279 raw_spin_lock_nested(&stopper2->lock, <<
280 236
281 if (!stopper1->enabled || !stopper2->e !! 237 err = -ENOENT;
282 err = -ENOENT; !! 238 if (!stopper1->enabled || !stopper2->enabled)
283 goto unlock; 239 goto unlock;
284 } <<
285 <<
286 /* 240 /*
287 * Ensure that if we race with __stop_ 241 * Ensure that if we race with __stop_cpus() the stoppers won't get
288 * queued up in reverse order leading 242 * queued up in reverse order leading to system deadlock.
289 * 243 *
290 * We can't miss stop_cpus_in_progress 244 * We can't miss stop_cpus_in_progress if queue_stop_cpus_work() has
291 * queued a work on cpu1 but not on cp 245 * queued a work on cpu1 but not on cpu2, we hold both locks.
292 * 246 *
293 * It can be falsely true but it is sa 247 * It can be falsely true but it is safe to spin until it is cleared,
294 * queue_stop_cpus_work() does everyth 248 * queue_stop_cpus_work() does everything under preempt_disable().
295 */ 249 */
296 if (unlikely(stop_cpus_in_progress)) { !! 250 err = -EDEADLK;
297 err = -EDEADLK; !! 251 if (unlikely(stop_cpus_in_progress))
298 goto unlock; !! 252 goto unlock;
299 } <<
300 253
301 err = 0; 254 err = 0;
302 __cpu_stop_queue_work(stopper1, work1, !! 255 __cpu_stop_queue_work(stopper1, work1);
303 __cpu_stop_queue_work(stopper2, work2, !! 256 __cpu_stop_queue_work(stopper2, work2);
304 <<
305 unlock: 257 unlock:
306 raw_spin_unlock(&stopper2->lock); !! 258 spin_unlock(&stopper2->lock);
307 raw_spin_unlock_irq(&stopper1->lock); !! 259 spin_unlock_irq(&stopper1->lock);
308 260
309 if (unlikely(err == -EDEADLK)) { 261 if (unlikely(err == -EDEADLK)) {
310 preempt_enable(); <<
311 <<
312 while (stop_cpus_in_progress) 262 while (stop_cpus_in_progress)
313 cpu_relax(); 263 cpu_relax();
314 <<
315 goto retry; 264 goto retry;
316 } 265 }
317 <<
318 wake_up_q(&wakeq); <<
319 preempt_enable(); <<
320 <<
321 return err; 266 return err;
322 } 267 }
323 /** 268 /**
324 * stop_two_cpus - stops two cpus 269 * stop_two_cpus - stops two cpus
325 * @cpu1: the cpu to stop 270 * @cpu1: the cpu to stop
326 * @cpu2: the other cpu to stop 271 * @cpu2: the other cpu to stop
327 * @fn: function to execute 272 * @fn: function to execute
328 * @arg: argument to @fn 273 * @arg: argument to @fn
329 * 274 *
330 * Stops both the current and specified CPU an 275 * Stops both the current and specified CPU and runs @fn on one of them.
331 * 276 *
332 * returns when both are completed. 277 * returns when both are completed.
333 */ 278 */
334 int stop_two_cpus(unsigned int cpu1, unsigned 279 int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *arg)
335 { 280 {
336 struct cpu_stop_done done; 281 struct cpu_stop_done done;
337 struct cpu_stop_work work1, work2; 282 struct cpu_stop_work work1, work2;
338 struct multi_stop_data msdata; 283 struct multi_stop_data msdata;
339 284
340 msdata = (struct multi_stop_data){ 285 msdata = (struct multi_stop_data){
341 .fn = fn, 286 .fn = fn,
342 .data = arg, 287 .data = arg,
343 .num_threads = 2, 288 .num_threads = 2,
344 .active_cpus = cpumask_of(cpu1 289 .active_cpus = cpumask_of(cpu1),
345 }; 290 };
346 291
347 work1 = work2 = (struct cpu_stop_work) 292 work1 = work2 = (struct cpu_stop_work){
348 .fn = multi_cpu_stop, 293 .fn = multi_cpu_stop,
349 .arg = &msdata, 294 .arg = &msdata,
350 .done = &done, !! 295 .done = &done
351 .caller = _RET_IP_, <<
352 }; 296 };
353 297
354 cpu_stop_init_done(&done, 2); 298 cpu_stop_init_done(&done, 2);
355 set_state(&msdata, MULTI_STOP_PREPARE) 299 set_state(&msdata, MULTI_STOP_PREPARE);
356 300
357 if (cpu1 > cpu2) 301 if (cpu1 > cpu2)
358 swap(cpu1, cpu2); 302 swap(cpu1, cpu2);
359 if (cpu_stop_queue_two_works(cpu1, &wo 303 if (cpu_stop_queue_two_works(cpu1, &work1, cpu2, &work2))
360 return -ENOENT; 304 return -ENOENT;
361 305
362 wait_for_completion(&done.completion); 306 wait_for_completion(&done.completion);
363 return done.ret; 307 return done.ret;
364 } 308 }
365 309
366 /** 310 /**
367 * stop_one_cpu_nowait - stop a cpu but don't 311 * stop_one_cpu_nowait - stop a cpu but don't wait for completion
368 * @cpu: cpu to stop 312 * @cpu: cpu to stop
369 * @fn: function to execute 313 * @fn: function to execute
370 * @arg: argument to @fn 314 * @arg: argument to @fn
371 * @work_buf: pointer to cpu_stop_work structu 315 * @work_buf: pointer to cpu_stop_work structure
372 * 316 *
373 * Similar to stop_one_cpu() but doesn't wait 317 * Similar to stop_one_cpu() but doesn't wait for completion. The
374 * caller is responsible for ensuring @work_bu 318 * caller is responsible for ensuring @work_buf is currently unused
375 * and will remain untouched until stopper sta 319 * and will remain untouched until stopper starts executing @fn.
376 * 320 *
377 * CONTEXT: 321 * CONTEXT:
378 * Don't care. 322 * Don't care.
379 * 323 *
380 * RETURNS: 324 * RETURNS:
381 * true if cpu_stop_work was queued successful 325 * true if cpu_stop_work was queued successfully and @fn will be called,
382 * false otherwise. 326 * false otherwise.
383 */ 327 */
384 bool stop_one_cpu_nowait(unsigned int cpu, cpu 328 bool stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
385 struct cpu_stop_work * 329 struct cpu_stop_work *work_buf)
386 { 330 {
387 *work_buf = (struct cpu_stop_work){ .f !! 331 *work_buf = (struct cpu_stop_work){ .fn = fn, .arg = arg, };
388 return cpu_stop_queue_work(cpu, work_b 332 return cpu_stop_queue_work(cpu, work_buf);
389 } 333 }
390 334
391 static bool queue_stop_cpus_work(const struct 335 static bool queue_stop_cpus_work(const struct cpumask *cpumask,
392 cpu_stop_fn_t 336 cpu_stop_fn_t fn, void *arg,
393 struct cpu_st 337 struct cpu_stop_done *done)
394 { 338 {
395 struct cpu_stop_work *work; 339 struct cpu_stop_work *work;
396 unsigned int cpu; 340 unsigned int cpu;
397 bool queued = false; 341 bool queued = false;
398 342
399 /* 343 /*
400 * Disable preemption while queueing t 344 * Disable preemption while queueing to avoid getting
401 * preempted by a stopper which might 345 * preempted by a stopper which might wait for other stoppers
402 * to enter @fn which can lead to dead 346 * to enter @fn which can lead to deadlock.
403 */ 347 */
404 preempt_disable(); 348 preempt_disable();
405 stop_cpus_in_progress = true; 349 stop_cpus_in_progress = true;
406 barrier(); <<
407 for_each_cpu(cpu, cpumask) { 350 for_each_cpu(cpu, cpumask) {
408 work = &per_cpu(cpu_stopper.st 351 work = &per_cpu(cpu_stopper.stop_work, cpu);
409 work->fn = fn; 352 work->fn = fn;
410 work->arg = arg; 353 work->arg = arg;
411 work->done = done; 354 work->done = done;
412 work->caller = _RET_IP_; <<
413 if (cpu_stop_queue_work(cpu, w 355 if (cpu_stop_queue_work(cpu, work))
414 queued = true; 356 queued = true;
415 } 357 }
416 barrier(); <<
417 stop_cpus_in_progress = false; 358 stop_cpus_in_progress = false;
418 preempt_enable(); 359 preempt_enable();
419 360
420 return queued; 361 return queued;
421 } 362 }
422 363
423 static int __stop_cpus(const struct cpumask *c 364 static int __stop_cpus(const struct cpumask *cpumask,
424 cpu_stop_fn_t fn, void 365 cpu_stop_fn_t fn, void *arg)
425 { 366 {
426 struct cpu_stop_done done; 367 struct cpu_stop_done done;
427 368
428 cpu_stop_init_done(&done, cpumask_weig 369 cpu_stop_init_done(&done, cpumask_weight(cpumask));
429 if (!queue_stop_cpus_work(cpumask, fn, 370 if (!queue_stop_cpus_work(cpumask, fn, arg, &done))
430 return -ENOENT; 371 return -ENOENT;
431 wait_for_completion(&done.completion); 372 wait_for_completion(&done.completion);
432 return done.ret; 373 return done.ret;
433 } 374 }
434 375
435 /** 376 /**
436 * stop_cpus - stop multiple cpus 377 * stop_cpus - stop multiple cpus
437 * @cpumask: cpus to stop 378 * @cpumask: cpus to stop
438 * @fn: function to execute 379 * @fn: function to execute
439 * @arg: argument to @fn 380 * @arg: argument to @fn
440 * 381 *
441 * Execute @fn(@arg) on online cpus in @cpumas 382 * Execute @fn(@arg) on online cpus in @cpumask. On each target cpu,
442 * @fn is run in a process context with the hi 383 * @fn is run in a process context with the highest priority
443 * preempting any task on the cpu and monopoli 384 * preempting any task on the cpu and monopolizing it. This function
444 * returns after all executions are complete. 385 * returns after all executions are complete.
445 * 386 *
446 * This function doesn't guarantee the cpus in 387 * This function doesn't guarantee the cpus in @cpumask stay online
447 * till @fn completes. If some cpus go down i 388 * till @fn completes. If some cpus go down in the middle, execution
448 * on the cpu may happen partially or fully on 389 * on the cpu may happen partially or fully on different cpus. @fn
449 * should either be ready for that or the call 390 * should either be ready for that or the caller should ensure that
450 * the cpus stay online until this function co 391 * the cpus stay online until this function completes.
451 * 392 *
452 * All stop_cpus() calls are serialized making 393 * All stop_cpus() calls are serialized making it safe for @fn to wait
453 * for all cpus to start executing it. 394 * for all cpus to start executing it.
454 * 395 *
455 * CONTEXT: 396 * CONTEXT:
456 * Might sleep. 397 * Might sleep.
457 * 398 *
458 * RETURNS: 399 * RETURNS:
459 * -ENOENT if @fn(@arg) was not executed at al 400 * -ENOENT if @fn(@arg) was not executed at all because all cpus in
460 * @cpumask were offline; otherwise, 0 if all 401 * @cpumask were offline; otherwise, 0 if all executions of @fn
461 * returned 0, any non zero return value if an 402 * returned 0, any non zero return value if any returned non zero.
462 */ 403 */
463 static int stop_cpus(const struct cpumask *cpu !! 404 int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
464 { 405 {
465 int ret; 406 int ret;
466 407
467 /* static works are used, process one 408 /* static works are used, process one request at a time */
468 mutex_lock(&stop_cpus_mutex); 409 mutex_lock(&stop_cpus_mutex);
469 ret = __stop_cpus(cpumask, fn, arg); 410 ret = __stop_cpus(cpumask, fn, arg);
470 mutex_unlock(&stop_cpus_mutex); 411 mutex_unlock(&stop_cpus_mutex);
471 return ret; 412 return ret;
472 } 413 }
473 414
>> 415 /**
>> 416 * try_stop_cpus - try to stop multiple cpus
>> 417 * @cpumask: cpus to stop
>> 418 * @fn: function to execute
>> 419 * @arg: argument to @fn
>> 420 *
>> 421 * Identical to stop_cpus() except that it fails with -EAGAIN if
>> 422 * someone else is already using the facility.
>> 423 *
>> 424 * CONTEXT:
>> 425 * Might sleep.
>> 426 *
>> 427 * RETURNS:
>> 428 * -EAGAIN if someone else is already stopping cpus, -ENOENT if
>> 429 * @fn(@arg) was not executed at all because all cpus in @cpumask were
>> 430 * offline; otherwise, 0 if all executions of @fn returned 0, any non
>> 431 * zero return value if any returned non zero.
>> 432 */
>> 433 int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
>> 434 {
>> 435 int ret;
>> 436
>> 437 /* static works are used, process one request at a time */
>> 438 if (!mutex_trylock(&stop_cpus_mutex))
>> 439 return -EAGAIN;
>> 440 ret = __stop_cpus(cpumask, fn, arg);
>> 441 mutex_unlock(&stop_cpus_mutex);
>> 442 return ret;
>> 443 }
>> 444
474 static int cpu_stop_should_run(unsigned int cp 445 static int cpu_stop_should_run(unsigned int cpu)
475 { 446 {
476 struct cpu_stopper *stopper = &per_cpu 447 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
477 unsigned long flags; 448 unsigned long flags;
478 int run; 449 int run;
479 450
480 raw_spin_lock_irqsave(&stopper->lock, !! 451 spin_lock_irqsave(&stopper->lock, flags);
481 run = !list_empty(&stopper->works); 452 run = !list_empty(&stopper->works);
482 raw_spin_unlock_irqrestore(&stopper->l !! 453 spin_unlock_irqrestore(&stopper->lock, flags);
483 return run; 454 return run;
484 } 455 }
485 456
486 static void cpu_stopper_thread(unsigned int cp 457 static void cpu_stopper_thread(unsigned int cpu)
487 { 458 {
488 struct cpu_stopper *stopper = &per_cpu 459 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
489 struct cpu_stop_work *work; 460 struct cpu_stop_work *work;
490 461
491 repeat: 462 repeat:
492 work = NULL; 463 work = NULL;
493 raw_spin_lock_irq(&stopper->lock); !! 464 spin_lock_irq(&stopper->lock);
494 if (!list_empty(&stopper->works)) { 465 if (!list_empty(&stopper->works)) {
495 work = list_first_entry(&stopp 466 work = list_first_entry(&stopper->works,
496 struct 467 struct cpu_stop_work, list);
497 list_del_init(&work->list); 468 list_del_init(&work->list);
498 } 469 }
499 raw_spin_unlock_irq(&stopper->lock); !! 470 spin_unlock_irq(&stopper->lock);
500 471
501 if (work) { 472 if (work) {
502 cpu_stop_fn_t fn = work->fn; 473 cpu_stop_fn_t fn = work->fn;
503 void *arg = work->arg; 474 void *arg = work->arg;
504 struct cpu_stop_done *done = w 475 struct cpu_stop_done *done = work->done;
505 int ret; 476 int ret;
506 477
507 /* cpu stop callbacks must not 478 /* cpu stop callbacks must not sleep, make in_atomic() == T */
508 stopper->caller = work->caller <<
509 stopper->fn = fn; <<
510 preempt_count_inc(); 479 preempt_count_inc();
511 ret = fn(arg); 480 ret = fn(arg);
512 if (done) { 481 if (done) {
513 if (ret) 482 if (ret)
514 done->ret = re 483 done->ret = ret;
515 cpu_stop_signal_done(d 484 cpu_stop_signal_done(done);
516 } 485 }
517 preempt_count_dec(); 486 preempt_count_dec();
518 stopper->fn = NULL; <<
519 stopper->caller = 0; <<
520 WARN_ONCE(preempt_count(), 487 WARN_ONCE(preempt_count(),
521 "cpu_stop: %ps(%p) l !! 488 "cpu_stop: %pf(%p) leaked preempt count\n", fn, arg);
522 goto repeat; 489 goto repeat;
523 } 490 }
524 } 491 }
525 492
526 void stop_machine_park(int cpu) 493 void stop_machine_park(int cpu)
527 { 494 {
528 struct cpu_stopper *stopper = &per_cpu 495 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
529 /* 496 /*
530 * Lockless. cpu_stopper_thread() will 497 * Lockless. cpu_stopper_thread() will take stopper->lock and flush
531 * the pending works before it parks, 498 * the pending works before it parks, until then it is fine to queue
532 * the new works. 499 * the new works.
533 */ 500 */
534 stopper->enabled = false; 501 stopper->enabled = false;
535 kthread_park(stopper->thread); 502 kthread_park(stopper->thread);
536 } 503 }
537 504
>> 505 extern void sched_set_stop_task(int cpu, struct task_struct *stop);
>> 506
538 static void cpu_stop_create(unsigned int cpu) 507 static void cpu_stop_create(unsigned int cpu)
539 { 508 {
540 sched_set_stop_task(cpu, per_cpu(cpu_s 509 sched_set_stop_task(cpu, per_cpu(cpu_stopper.thread, cpu));
541 } 510 }
542 511
543 static void cpu_stop_park(unsigned int cpu) 512 static void cpu_stop_park(unsigned int cpu)
544 { 513 {
545 struct cpu_stopper *stopper = &per_cpu 514 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
546 515
547 WARN_ON(!list_empty(&stopper->works)); 516 WARN_ON(!list_empty(&stopper->works));
548 } 517 }
549 518
550 void stop_machine_unpark(int cpu) 519 void stop_machine_unpark(int cpu)
551 { 520 {
552 struct cpu_stopper *stopper = &per_cpu 521 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
553 522
554 stopper->enabled = true; 523 stopper->enabled = true;
555 kthread_unpark(stopper->thread); 524 kthread_unpark(stopper->thread);
556 } 525 }
557 526
558 static struct smp_hotplug_thread cpu_stop_thre 527 static struct smp_hotplug_thread cpu_stop_threads = {
559 .store = &cpu_stopper 528 .store = &cpu_stopper.thread,
560 .thread_should_run = cpu_stop_sho 529 .thread_should_run = cpu_stop_should_run,
561 .thread_fn = cpu_stopper_ 530 .thread_fn = cpu_stopper_thread,
562 .thread_comm = "migration/% 531 .thread_comm = "migration/%u",
563 .create = cpu_stop_cre 532 .create = cpu_stop_create,
564 .park = cpu_stop_par 533 .park = cpu_stop_park,
565 .selfparking = true, 534 .selfparking = true,
566 }; 535 };
567 536
568 static int __init cpu_stop_init(void) 537 static int __init cpu_stop_init(void)
569 { 538 {
570 unsigned int cpu; 539 unsigned int cpu;
571 540
572 for_each_possible_cpu(cpu) { 541 for_each_possible_cpu(cpu) {
573 struct cpu_stopper *stopper = 542 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
574 543
575 raw_spin_lock_init(&stopper->l !! 544 spin_lock_init(&stopper->lock);
576 INIT_LIST_HEAD(&stopper->works 545 INIT_LIST_HEAD(&stopper->works);
577 } 546 }
578 547
579 BUG_ON(smpboot_register_percpu_thread( 548 BUG_ON(smpboot_register_percpu_thread(&cpu_stop_threads));
580 stop_machine_unpark(raw_smp_processor_ 549 stop_machine_unpark(raw_smp_processor_id());
581 stop_machine_initialized = true; 550 stop_machine_initialized = true;
582 return 0; 551 return 0;
583 } 552 }
584 early_initcall(cpu_stop_init); 553 early_initcall(cpu_stop_init);
585 554
586 int stop_machine_cpuslocked(cpu_stop_fn_t fn, !! 555 static int __stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)
587 const struct cpuma <<
588 { 556 {
589 struct multi_stop_data msdata = { 557 struct multi_stop_data msdata = {
590 .fn = fn, 558 .fn = fn,
591 .data = data, 559 .data = data,
592 .num_threads = num_online_cpus 560 .num_threads = num_online_cpus(),
593 .active_cpus = cpus, 561 .active_cpus = cpus,
594 }; 562 };
595 563
596 lockdep_assert_cpus_held(); <<
597 <<
598 if (!stop_machine_initialized) { 564 if (!stop_machine_initialized) {
599 /* 565 /*
600 * Handle the case where stop_ 566 * Handle the case where stop_machine() is called
601 * early in boot before stop_m 567 * early in boot before stop_machine() has been
602 * initialized. 568 * initialized.
603 */ 569 */
604 unsigned long flags; 570 unsigned long flags;
605 int ret; 571 int ret;
606 572
607 WARN_ON_ONCE(msdata.num_thread 573 WARN_ON_ONCE(msdata.num_threads != 1);
608 574
609 local_irq_save(flags); 575 local_irq_save(flags);
610 hard_irq_disable(); 576 hard_irq_disable();
611 ret = (*fn)(data); 577 ret = (*fn)(data);
612 local_irq_restore(flags); 578 local_irq_restore(flags);
613 579
614 return ret; 580 return ret;
615 } 581 }
616 582
617 /* Set the initial state and stop all 583 /* Set the initial state and stop all online cpus. */
618 set_state(&msdata, MULTI_STOP_PREPARE) 584 set_state(&msdata, MULTI_STOP_PREPARE);
619 return stop_cpus(cpu_online_mask, mult 585 return stop_cpus(cpu_online_mask, multi_cpu_stop, &msdata);
620 } 586 }
621 587
622 int stop_machine(cpu_stop_fn_t fn, void *data, 588 int stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)
623 { 589 {
624 int ret; 590 int ret;
625 591
626 /* No CPUs can come up or down during 592 /* No CPUs can come up or down during this. */
627 cpus_read_lock(); !! 593 get_online_cpus();
628 ret = stop_machine_cpuslocked(fn, data !! 594 ret = __stop_machine(fn, data, cpus);
629 cpus_read_unlock(); !! 595 put_online_cpus();
630 return ret; 596 return ret;
631 } 597 }
632 EXPORT_SYMBOL_GPL(stop_machine); 598 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 <<
654 599
655 /** 600 /**
656 * stop_machine_from_inactive_cpu - stop_machi 601 * stop_machine_from_inactive_cpu - stop_machine() from inactive CPU
657 * @fn: the function to run 602 * @fn: the function to run
658 * @data: the data ptr for the @fn() 603 * @data: the data ptr for the @fn()
659 * @cpus: the cpus to run the @fn() on (NULL = 604 * @cpus: the cpus to run the @fn() on (NULL = any online cpu)
660 * 605 *
661 * This is identical to stop_machine() but can 606 * 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 607 * is not active. The local CPU is in the process of hotplug (so no other
663 * CPU hotplug can start) and not marked activ 608 * CPU hotplug can start) and not marked active and doesn't have enough
664 * context to sleep. 609 * context to sleep.
665 * 610 *
666 * This function provides stop_machine() funct 611 * This function provides stop_machine() functionality for such state by
667 * using busy-wait for synchronization and exe 612 * using busy-wait for synchronization and executing @fn directly for local
668 * CPU. 613 * CPU.
669 * 614 *
670 * CONTEXT: 615 * CONTEXT:
671 * Local CPU is inactive. Temporarily stops a 616 * Local CPU is inactive. Temporarily stops all active CPUs.
672 * 617 *
673 * RETURNS: 618 * RETURNS:
674 * 0 if all executions of @fn returned 0, any 619 * 0 if all executions of @fn returned 0, any non zero return value if any
675 * returned non zero. 620 * returned non zero.
676 */ 621 */
677 int stop_machine_from_inactive_cpu(cpu_stop_fn 622 int stop_machine_from_inactive_cpu(cpu_stop_fn_t fn, void *data,
678 const struct 623 const struct cpumask *cpus)
679 { 624 {
680 struct multi_stop_data msdata = { .fn 625 struct multi_stop_data msdata = { .fn = fn, .data = data,
681 .a 626 .active_cpus = cpus };
682 struct cpu_stop_done done; 627 struct cpu_stop_done done;
683 int ret; 628 int ret;
684 629
685 /* Local CPU must be inactive and CPU 630 /* Local CPU must be inactive and CPU hotplug in progress. */
686 BUG_ON(cpu_active(raw_smp_processor_id 631 BUG_ON(cpu_active(raw_smp_processor_id()));
687 msdata.num_threads = num_active_cpus() 632 msdata.num_threads = num_active_cpus() + 1; /* +1 for local */
688 633
689 /* No proper task established and can' 634 /* No proper task established and can't sleep - busy wait for lock. */
690 while (!mutex_trylock(&stop_cpus_mutex 635 while (!mutex_trylock(&stop_cpus_mutex))
691 cpu_relax(); 636 cpu_relax();
692 637
693 /* Schedule work on other CPUs and exe 638 /* Schedule work on other CPUs and execute directly for local CPU */
694 set_state(&msdata, MULTI_STOP_PREPARE) 639 set_state(&msdata, MULTI_STOP_PREPARE);
695 cpu_stop_init_done(&done, num_active_c 640 cpu_stop_init_done(&done, num_active_cpus());
696 queue_stop_cpus_work(cpu_active_mask, 641 queue_stop_cpus_work(cpu_active_mask, multi_cpu_stop, &msdata,
697 &done); 642 &done);
698 ret = multi_cpu_stop(&msdata); 643 ret = multi_cpu_stop(&msdata);
699 644
700 /* Busy wait for completion. */ 645 /* Busy wait for completion. */
701 while (!completion_done(&done.completi 646 while (!completion_done(&done.completion))
702 cpu_relax(); 647 cpu_relax();
703 648
704 mutex_unlock(&stop_cpus_mutex); 649 mutex_unlock(&stop_cpus_mutex);
705 return ret ?: done.ret; 650 return ret ?: done.ret;
706 } 651 }
707 652
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