kernel/sched/membarrier.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * Copyright (C) 2010-2017 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   4  *
   5  * membarrier system call
   6  */
   7 #include "sched.h"
   8
   9 /*
  10  * Bitmask made from a "or" of all commands within enum membarrier_cmd,
  11  * except MEMBARRIER_CMD_QUERY.
  12  */
  13 #ifdef CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE
  14 #define MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK                  \
  15         (MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE                     \
  16         | MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE)
  17 #else
  18 #define MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK  0
  19 #endif
  20
  21 #ifdef CONFIG_RSEQ
  22 #define MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ_BITMASK           \
  23         (MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ                  \
  24         | MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_RSEQ_BITMASK)
  25 #else
  26 #define MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ_BITMASK   0
  27 #endif
  28
  29 #define MEMBARRIER_CMD_BITMASK                                          \
  30         (MEMBARRIER_CMD_GLOBAL | MEMBARRIER_CMD_GLOBAL_EXPEDITED        \
  31         | MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED                      \
  32         | MEMBARRIER_CMD_PRIVATE_EXPEDITED                              \
  33         | MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED                     \
  34         | MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK)
  35
  36 static void ipi_mb(void *info)
  37 {
  38         smp_mb();       /* IPIs should be serializing but paranoid. */
  39 }
  40
  41 static void ipi_rseq(void *info)
  42 {
  43         rseq_preempt(current);
  44 }
  45
  46 static void ipi_sync_rq_state(void *info)
  47 {
  48         struct mm_struct *mm = (struct mm_struct *) info;
  49
  50         if (current->mm != mm)
  51                 return;
  52         this_cpu_write(runqueues.membarrier_state,
  53                        atomic_read(&mm->membarrier_state));
  54         /*
  55          * Issue a memory barrier after setting
  56          * MEMBARRIER_STATE_GLOBAL_EXPEDITED in the current runqueue to
  57          * guarantee that no memory access following registration is reordered
  58          * before registration.
  59          */
  60         smp_mb();
  61 }
  62
  63 void membarrier_exec_mmap(struct mm_struct *mm)
  64 {
  65         /*
  66          * Issue a memory barrier before clearing membarrier_state to
  67          * guarantee that no memory access prior to exec is reordered after
  68          * clearing this state.
  69          */
  70         smp_mb();
  71         atomic_set(&mm->membarrier_state, 0);
  72         /*
  73          * Keep the runqueue membarrier_state in sync with this mm
  74          * membarrier_state.
  75          */
  76         this_cpu_write(runqueues.membarrier_state, 0);
  77 }
  78
  79 static int membarrier_global_expedited(void)
  80 {
  81         int cpu;
  82         cpumask_var_t tmpmask;
  83
  84         if (num_online_cpus() == 1)
  85                 return 0;
  86
  87         /*
  88          * Matches memory barriers around rq->curr modification in
  89          * scheduler.
  90          */
  91         smp_mb();       /* system call entry is not a mb. */
  92
  93         if (!zalloc_cpumask_var(&tmpmask, GFP_KERNEL))
  94                 return -ENOMEM;
  95
  96         cpus_read_lock();
  97         rcu_read_lock();
  98         for_each_online_cpu(cpu) {
  99                 struct task_struct *p;
 100
 101                 /*
 102                  * Skipping the current CPU is OK even through we can be
 103                  * migrated at any point. The current CPU, at the point
 104                  * where we read raw_smp_processor_id(), is ensured to
 105                  * be in program order with respect to the caller
 106                  * thread. Therefore, we can skip this CPU from the
 107                  * iteration.
 108                  */
 109                 if (cpu == raw_smp_processor_id())
 110                         continue;
 111
 112                 if (!(READ_ONCE(cpu_rq(cpu)->membarrier_state) &
 113                     MEMBARRIER_STATE_GLOBAL_EXPEDITED))
 114                         continue;
 115
 116                 /*
 117                  * Skip the CPU if it runs a kernel thread. The scheduler
 118                  * leaves the prior task mm in place as an optimization when
 119                  * scheduling a kthread.
 120                  */
 121                 p = rcu_dereference(cpu_rq(cpu)->curr);
 122                 if (p->flags & PF_KTHREAD)
 123                         continue;
 124
 125                 __cpumask_set_cpu(cpu, tmpmask);
 126         }
 127         rcu_read_unlock();
 128
 129         preempt_disable();
 130         smp_call_function_many(tmpmask, ipi_mb, NULL, 1);
 131         preempt_enable();
 132
 133         free_cpumask_var(tmpmask);
 134         cpus_read_unlock();
 135
 136         /*
 137          * Memory barrier on the caller thread _after_ we finished
 138          * waiting for the last IPI. Matches memory barriers around
 139          * rq->curr modification in scheduler.
 140          */
 141         smp_mb();       /* exit from system call is not a mb */
 142         return 0;
 143 }
 144
 145 static int membarrier_private_expedited(int flags, int cpu_id)
 146 {
 147         cpumask_var_t tmpmask;
 148         struct mm_struct *mm = current->mm;
 149         smp_call_func_t ipi_func = ipi_mb;
 150
 151         if (flags == MEMBARRIER_FLAG_SYNC_CORE) {
 152                 if (!IS_ENABLED(CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE))
 153                         return -EINVAL;
 154                 if (!(atomic_read(&mm->membarrier_state) &
 155                       MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY))
 156                         return -EPERM;
 157         } else if (flags == MEMBARRIER_FLAG_RSEQ) {
 158                 if (!IS_ENABLED(CONFIG_RSEQ))
 159                         return -EINVAL;
 160                 if (!(atomic_read(&mm->membarrier_state) &
 161                       MEMBARRIER_STATE_PRIVATE_EXPEDITED_RSEQ_READY))
 162                         return -EPERM;
 163                 ipi_func = ipi_rseq;
 164         } else {
 165                 WARN_ON_ONCE(flags);
 166                 if (!(atomic_read(&mm->membarrier_state) &
 167                       MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY))
 168                         return -EPERM;
 169         }
 170
 171         if (atomic_read(&mm->mm_users) == 1 || num_online_cpus() == 1)
 172                 return 0;
 173
 174         /*
 175          * Matches memory barriers around rq->curr modification in
 176          * scheduler.
 177          */
 178         smp_mb();       /* system call entry is not a mb. */
 179
 180         if (cpu_id < 0 && !zalloc_cpumask_var(&tmpmask, GFP_KERNEL))
 181                 return -ENOMEM;
 182
 183         cpus_read_lock();
 184
 185         if (cpu_id >= 0) {
 186                 struct task_struct *p;
 187
 188                 if (cpu_id >= nr_cpu_ids || !cpu_online(cpu_id))
 189                         goto out;
 190                 if (cpu_id == raw_smp_processor_id())
 191                         goto out;
 192                 rcu_read_lock();
 193                 p = rcu_dereference(cpu_rq(cpu_id)->curr);
 194                 if (!p || p->mm != mm) {
 195                         rcu_read_unlock();
 196                         goto out;
 197                 }
 198                 rcu_read_unlock();
 199         } else {
 200                 int cpu;
 201
 202                 rcu_read_lock();
 203                 for_each_online_cpu(cpu) {
 204                         struct task_struct *p;
 205
 206                         /*
 207                          * Skipping the current CPU is OK even through we can be
 208                          * migrated at any point. The current CPU, at the point
 209                          * where we read raw_smp_processor_id(), is ensured to
 210                          * be in program order with respect to the caller
 211                          * thread. Therefore, we can skip this CPU from the
 212                          * iteration.
 213                          */
 214                         if (cpu == raw_smp_processor_id())
 215                                 continue;
 216                         p = rcu_dereference(cpu_rq(cpu)->curr);
 217                         if (p && p->mm == mm)
 218                                 __cpumask_set_cpu(cpu, tmpmask);
 219                 }
 220                 rcu_read_unlock();
 221         }
 222
 223         preempt_disable();
 224         if (cpu_id >= 0)
 225                 smp_call_function_single(cpu_id, ipi_func, NULL, 1);
 226         else
 227                 smp_call_function_many(tmpmask, ipi_func, NULL, 1);
 228         preempt_enable();
 229
 230 out:
 231         if (cpu_id < 0)
 232                 free_cpumask_var(tmpmask);
 233         cpus_read_unlock();
 234
 235         /*
 236          * Memory barrier on the caller thread _after_ we finished
 237          * waiting for the last IPI. Matches memory barriers around
 238          * rq->curr modification in scheduler.
 239          */
 240         smp_mb();       /* exit from system call is not a mb */
 241
 242         return 0;
 243 }
 244
 245 static int sync_runqueues_membarrier_state(struct mm_struct *mm)
 246 {
 247         int membarrier_state = atomic_read(&mm->membarrier_state);
 248         cpumask_var_t tmpmask;
 249         int cpu;
 250
 251         if (atomic_read(&mm->mm_users) == 1 || num_online_cpus() == 1) {
 252                 this_cpu_write(runqueues.membarrier_state, membarrier_state);
 253
 254                 /*
 255                  * For single mm user, we can simply issue a memory barrier
 256                  * after setting MEMBARRIER_STATE_GLOBAL_EXPEDITED in the
 257                  * mm and in the current runqueue to guarantee that no memory
 258                  * access following registration is reordered before
 259                  * registration.
 260                  */
 261                 smp_mb();
 262                 return 0;
 263         }
 264
 265         if (!zalloc_cpumask_var(&tmpmask, GFP_KERNEL))
 266                 return -ENOMEM;
 267
 268         /*
 269          * For mm with multiple users, we need to ensure all future
 270          * scheduler executions will observe @mm's new membarrier
 271          * state.
 272          */
 273         synchronize_rcu();
 274
 275         /*
 276          * For each cpu runqueue, if the task's mm match @mm, ensure that all
 277          * @mm's membarrier state set bits are also set in in the runqueue's
 278          * membarrier state. This ensures that a runqueue scheduling
 279          * between threads which are users of @mm has its membarrier state
 280          * updated.
 281          */
 282         cpus_read_lock();
 283         rcu_read_lock();
 284         for_each_online_cpu(cpu) {
 285                 struct rq *rq = cpu_rq(cpu);
 286                 struct task_struct *p;
 287
 288                 p = rcu_dereference(rq->curr);
 289                 if (p && p->mm == mm)
 290                         __cpumask_set_cpu(cpu, tmpmask);
 291         }
 292         rcu_read_unlock();
 293
 294         preempt_disable();
 295         smp_call_function_many(tmpmask, ipi_sync_rq_state, mm, 1);
 296         preempt_enable();
 297
 298         free_cpumask_var(tmpmask);
 299         cpus_read_unlock();
 300
 301         return 0;
 302 }
 303
 304 static int membarrier_register_global_expedited(void)
 305 {
 306         struct task_struct *p = current;
 307         struct mm_struct *mm = p->mm;
 308         int ret;
 309
 310         if (atomic_read(&mm->membarrier_state) &
 311             MEMBARRIER_STATE_GLOBAL_EXPEDITED_READY)
 312                 return 0;
 313         atomic_or(MEMBARRIER_STATE_GLOBAL_EXPEDITED, &mm->membarrier_state);
 314         ret = sync_runqueues_membarrier_state(mm);
 315         if (ret)
 316                 return ret;
 317         atomic_or(MEMBARRIER_STATE_GLOBAL_EXPEDITED_READY,
 318                   &mm->membarrier_state);
 319
 320         return 0;
 321 }
 322
 323 static int membarrier_register_private_expedited(int flags)
 324 {
 325         struct task_struct *p = current;
 326         struct mm_struct *mm = p->mm;
 327         int ready_state = MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY,
 328             set_state = MEMBARRIER_STATE_PRIVATE_EXPEDITED,
 329             ret;
 330
 331         if (flags == MEMBARRIER_FLAG_SYNC_CORE) {
 332                 if (!IS_ENABLED(CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE))
 333                         return -EINVAL;
 334                 ready_state =
 335                         MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY;
 336         } else if (flags == MEMBARRIER_FLAG_RSEQ) {
 337                 if (!IS_ENABLED(CONFIG_RSEQ))
 338                         return -EINVAL;
 339                 ready_state =
 340                         MEMBARRIER_STATE_PRIVATE_EXPEDITED_RSEQ_READY;
 341         } else {
 342                 WARN_ON_ONCE(flags);
 343         }
 344
 345         /*
 346          * We need to consider threads belonging to different thread
 347          * groups, which use the same mm. (CLONE_VM but not
 348          * CLONE_THREAD).
 349          */
 350         if ((atomic_read(&mm->membarrier_state) & ready_state) == ready_state)
 351                 return 0;
 352         if (flags & MEMBARRIER_FLAG_SYNC_CORE)
 353                 set_state |= MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE;
 354         if (flags & MEMBARRIER_FLAG_RSEQ)
 355                 set_state |= MEMBARRIER_STATE_PRIVATE_EXPEDITED_RSEQ;
 356         atomic_or(set_state, &mm->membarrier_state);
 357         ret = sync_runqueues_membarrier_state(mm);
 358         if (ret)
 359                 return ret;
 360         atomic_or(ready_state, &mm->membarrier_state);
 361
 362         return 0;
 363 }
 364
 365 /**
 366  * sys_membarrier - issue memory barriers on a set of threads
 367  * @cmd:    Takes command values defined in enum membarrier_cmd.
 368  * @flags:  Currently needs to be 0 for all commands other than
 369  *          MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ: in the latter
 370  *          case it can be MEMBARRIER_CMD_FLAG_CPU, indicating that @cpu_id
 371  *          contains the CPU on which to interrupt (= restart)
 372  *          the RSEQ critical section.
 373  * @cpu_id: if @flags == MEMBARRIER_CMD_FLAG_CPU, indicates the cpu on which
 374  *          RSEQ CS should be interrupted (@cmd must be
 375  *          MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ).
 376  *
 377  * If this system call is not implemented, -ENOSYS is returned. If the
 378  * command specified does not exist, not available on the running
 379  * kernel, or if the command argument is invalid, this system call
 380  * returns -EINVAL. For a given command, with flags argument set to 0,
 381  * if this system call returns -ENOSYS or -EINVAL, it is guaranteed to
 382  * always return the same value until reboot. In addition, it can return
 383  * -ENOMEM if there is not enough memory available to perform the system
 384  * call.
 385  *
 386  * All memory accesses performed in program order from each targeted thread
 387  * is guaranteed to be ordered with respect to sys_membarrier(). If we use
 388  * the semantic "barrier()" to represent a compiler barrier forcing memory
 389  * accesses to be performed in program order across the barrier, and
 390  * smp_mb() to represent explicit memory barriers forcing full memory
 391  * ordering across the barrier, we have the following ordering table for
 392  * each pair of barrier(), sys_membarrier() and smp_mb():
 393  *
 394  * The pair ordering is detailed as (O: ordered, X: not ordered):
 395  *
 396  *                        barrier()   smp_mb() sys_membarrier()
 397  *        barrier()          X           X            O
 398  *        smp_mb()           X           O            O
 399  *        sys_membarrier()   O           O            O
 400  */
 401 SYSCALL_DEFINE3(membarrier, int, cmd, unsigned int, flags, int, cpu_id)
 402 {
 403         switch (cmd) {
 404         case MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ:
 405                 if (unlikely(flags && flags != MEMBARRIER_CMD_FLAG_CPU))
 406                         return -EINVAL;
 407                 break;
 408         default:
 409                 if (unlikely(flags))
 410                         return -EINVAL;
 411         }
 412
 413         if (!(flags & MEMBARRIER_CMD_FLAG_CPU))
 414                 cpu_id = -1;
 415
 416         switch (cmd) {
 417         case MEMBARRIER_CMD_QUERY:
 418         {
 419                 int cmd_mask = MEMBARRIER_CMD_BITMASK;
 420
 421                 if (tick_nohz_full_enabled())
 422                         cmd_mask &= ~MEMBARRIER_CMD_GLOBAL;
 423                 return cmd_mask;
 424         }
 425         case MEMBARRIER_CMD_GLOBAL:
 426                 /* MEMBARRIER_CMD_GLOBAL is not compatible with nohz_full. */
 427                 if (tick_nohz_full_enabled())
 428                         return -EINVAL;
 429                 if (num_online_cpus() > 1)
 430                         synchronize_rcu();
 431                 return 0;
 432         case MEMBARRIER_CMD_GLOBAL_EXPEDITED:
 433                 return membarrier_global_expedited();
 434         case MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED:
 435                 return membarrier_register_global_expedited();
 436         case MEMBARRIER_CMD_PRIVATE_EXPEDITED:
 437                 return membarrier_private_expedited(0, cpu_id);
 438         case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED:
 439                 return membarrier_register_private_expedited(0);
 440         case MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE:
 441                 return membarrier_private_expedited(MEMBARRIER_FLAG_SYNC_CORE, cpu_id);
 442         case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE:
 443                 return membarrier_register_private_expedited(MEMBARRIER_FLAG_SYNC_CORE);
 444         case MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ:
 445                 return membarrier_private_expedited(MEMBARRIER_FLAG_RSEQ, cpu_id);
 446         case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_RSEQ:
 447                 return membarrier_register_private_expedited(MEMBARRIER_FLAG_RSEQ);
 448         default:
 449                 return -EINVAL;
 450         }
 451 }