LCOV - code coverage report
Current view: top level - kernel/sched - membarrier.c (source / functions) Hit Total Coverage
Test: gcov_data_raspi2_real_modules_combined.info Lines: 4 90 4.4 %
Date: 2020-09-30 20:25:40 Functions: 1 10 10.0 %
Branches: 0 65 0.0 %

           Branch data     Line data    Source code
       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                 :            : #define MEMBARRIER_CMD_BITMASK                                          \
      22                 :            :         (MEMBARRIER_CMD_GLOBAL | MEMBARRIER_CMD_GLOBAL_EXPEDITED        \
      23                 :            :         | MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED                      \
      24                 :            :         | MEMBARRIER_CMD_PRIVATE_EXPEDITED                              \
      25                 :            :         | MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED                     \
      26                 :            :         | MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK)
      27                 :            : 
      28                 :          0 : static void ipi_mb(void *info)
      29                 :            : {
      30                 :          0 :         smp_mb();       /* IPIs should be serializing but paranoid. */
      31                 :          0 : }
      32                 :            : 
      33                 :          0 : static void ipi_sync_rq_state(void *info)
      34                 :            : {
      35                 :            :         struct mm_struct *mm = (struct mm_struct *) info;
      36                 :            : 
      37         [ #  # ]:          0 :         if (current->mm != mm)
      38                 :          0 :                 return;
      39                 :          0 :         this_cpu_write(runqueues.membarrier_state,
      40                 :            :                        atomic_read(&mm->membarrier_state));
      41                 :            :         /*
      42                 :            :          * Issue a memory barrier after setting
      43                 :            :          * MEMBARRIER_STATE_GLOBAL_EXPEDITED in the current runqueue to
      44                 :            :          * guarantee that no memory access following registration is reordered
      45                 :            :          * before registration.
      46                 :            :          */
      47                 :          0 :         smp_mb();
      48                 :            : }
      49                 :            : 
      50                 :     151742 : void membarrier_exec_mmap(struct mm_struct *mm)
      51                 :            : {
      52                 :            :         /*
      53                 :            :          * Issue a memory barrier before clearing membarrier_state to
      54                 :            :          * guarantee that no memory access prior to exec is reordered after
      55                 :            :          * clearing this state.
      56                 :            :          */
      57                 :     151742 :         smp_mb();
      58                 :            :         atomic_set(&mm->membarrier_state, 0);
      59                 :            :         /*
      60                 :            :          * Keep the runqueue membarrier_state in sync with this mm
      61                 :            :          * membarrier_state.
      62                 :            :          */
      63                 :     303102 :         this_cpu_write(runqueues.membarrier_state, 0);
      64                 :     151647 : }
      65                 :            : 
      66                 :          0 : static int membarrier_global_expedited(void)
      67                 :            : {
      68                 :            :         int cpu;
      69                 :            :         cpumask_var_t tmpmask;
      70                 :            : 
      71         [ #  # ]:          0 :         if (num_online_cpus() == 1)
      72                 :            :                 return 0;
      73                 :            : 
      74                 :            :         /*
      75                 :            :          * Matches memory barriers around rq->curr modification in
      76                 :            :          * scheduler.
      77                 :            :          */
      78                 :          0 :         smp_mb();       /* system call entry is not a mb. */
      79                 :            : 
      80                 :            :         if (!zalloc_cpumask_var(&tmpmask, GFP_KERNEL))
      81                 :            :                 return -ENOMEM;
      82                 :            : 
      83                 :            :         cpus_read_lock();
      84                 :            :         rcu_read_lock();
      85         [ #  # ]:          0 :         for_each_online_cpu(cpu) {
      86                 :            :                 struct task_struct *p;
      87                 :            : 
      88                 :            :                 /*
      89                 :            :                  * Skipping the current CPU is OK even through we can be
      90                 :            :                  * migrated at any point. The current CPU, at the point
      91                 :            :                  * where we read raw_smp_processor_id(), is ensured to
      92                 :            :                  * be in program order with respect to the caller
      93                 :            :                  * thread. Therefore, we can skip this CPU from the
      94                 :            :                  * iteration.
      95                 :            :                  */
      96         [ #  # ]:          0 :                 if (cpu == raw_smp_processor_id())
      97                 :          0 :                         continue;
      98                 :            : 
      99         [ #  # ]:          0 :                 if (!(READ_ONCE(cpu_rq(cpu)->membarrier_state) &
     100                 :            :                     MEMBARRIER_STATE_GLOBAL_EXPEDITED))
     101                 :          0 :                         continue;
     102                 :            : 
     103                 :            :                 /*
     104                 :            :                  * Skip the CPU if it runs a kernel thread. The scheduler
     105                 :            :                  * leaves the prior task mm in place as an optimization when
     106                 :            :                  * scheduling a kthread.
     107                 :            :                  */
     108                 :          0 :                 p = rcu_dereference(cpu_rq(cpu)->curr);
     109         [ #  # ]:          0 :                 if (p->flags & PF_KTHREAD)
     110                 :          0 :                         continue;
     111                 :            : 
     112                 :            :                 __cpumask_set_cpu(cpu, tmpmask);
     113                 :            :         }
     114                 :            :         rcu_read_unlock();
     115                 :            : 
     116                 :          0 :         preempt_disable();
     117                 :          0 :         smp_call_function_many(tmpmask, ipi_mb, NULL, 1);
     118                 :          0 :         preempt_enable();
     119                 :            : 
     120                 :            :         free_cpumask_var(tmpmask);
     121                 :            :         cpus_read_unlock();
     122                 :            : 
     123                 :            :         /*
     124                 :            :          * Memory barrier on the caller thread _after_ we finished
     125                 :            :          * waiting for the last IPI. Matches memory barriers around
     126                 :            :          * rq->curr modification in scheduler.
     127                 :            :          */
     128                 :          0 :         smp_mb();       /* exit from system call is not a mb */
     129                 :          0 :         return 0;
     130                 :            : }
     131                 :            : 
     132                 :          0 : static int membarrier_private_expedited(int flags)
     133                 :            : {
     134                 :            :         int cpu;
     135                 :            :         cpumask_var_t tmpmask;
     136                 :          0 :         struct mm_struct *mm = current->mm;
     137                 :            : 
     138         [ #  # ]:          0 :         if (flags & MEMBARRIER_FLAG_SYNC_CORE) {
     139                 :            :                 if (!IS_ENABLED(CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE))
     140                 :            :                         return -EINVAL;
     141         [ #  # ]:          0 :                 if (!(atomic_read(&mm->membarrier_state) &
     142                 :            :                       MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY))
     143                 :            :                         return -EPERM;
     144                 :            :         } else {
     145         [ #  # ]:          0 :                 if (!(atomic_read(&mm->membarrier_state) &
     146                 :            :                       MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY))
     147                 :            :                         return -EPERM;
     148                 :            :         }
     149                 :            : 
     150   [ #  #  #  # ]:          0 :         if (atomic_read(&mm->mm_users) == 1 || num_online_cpus() == 1)
     151                 :            :                 return 0;
     152                 :            : 
     153                 :            :         /*
     154                 :            :          * Matches memory barriers around rq->curr modification in
     155                 :            :          * scheduler.
     156                 :            :          */
     157                 :          0 :         smp_mb();       /* system call entry is not a mb. */
     158                 :            : 
     159                 :            :         if (!zalloc_cpumask_var(&tmpmask, GFP_KERNEL))
     160                 :            :                 return -ENOMEM;
     161                 :            : 
     162                 :            :         cpus_read_lock();
     163                 :            :         rcu_read_lock();
     164         [ #  # ]:          0 :         for_each_online_cpu(cpu) {
     165                 :            :                 struct task_struct *p;
     166                 :            : 
     167                 :            :                 /*
     168                 :            :                  * Skipping the current CPU is OK even through we can be
     169                 :            :                  * migrated at any point. The current CPU, at the point
     170                 :            :                  * where we read raw_smp_processor_id(), is ensured to
     171                 :            :                  * be in program order with respect to the caller
     172                 :            :                  * thread. Therefore, we can skip this CPU from the
     173                 :            :                  * iteration.
     174                 :            :                  */
     175         [ #  # ]:          0 :                 if (cpu == raw_smp_processor_id())
     176                 :          0 :                         continue;
     177                 :          0 :                 p = rcu_dereference(cpu_rq(cpu)->curr);
     178   [ #  #  #  # ]:          0 :                 if (p && p->mm == mm)
     179                 :            :                         __cpumask_set_cpu(cpu, tmpmask);
     180                 :            :         }
     181                 :            :         rcu_read_unlock();
     182                 :            : 
     183                 :          0 :         preempt_disable();
     184                 :          0 :         smp_call_function_many(tmpmask, ipi_mb, NULL, 1);
     185                 :          0 :         preempt_enable();
     186                 :            : 
     187                 :            :         free_cpumask_var(tmpmask);
     188                 :            :         cpus_read_unlock();
     189                 :            : 
     190                 :            :         /*
     191                 :            :          * Memory barrier on the caller thread _after_ we finished
     192                 :            :          * waiting for the last IPI. Matches memory barriers around
     193                 :            :          * rq->curr modification in scheduler.
     194                 :            :          */
     195                 :          0 :         smp_mb();       /* exit from system call is not a mb */
     196                 :            : 
     197                 :          0 :         return 0;
     198                 :            : }
     199                 :            : 
     200                 :          0 : static int sync_runqueues_membarrier_state(struct mm_struct *mm)
     201                 :            : {
     202                 :          0 :         int membarrier_state = atomic_read(&mm->membarrier_state);
     203                 :            :         cpumask_var_t tmpmask;
     204                 :            :         int cpu;
     205                 :            : 
     206   [ #  #  #  # ]:          0 :         if (atomic_read(&mm->mm_users) == 1 || num_online_cpus() == 1) {
     207                 :          0 :                 this_cpu_write(runqueues.membarrier_state, membarrier_state);
     208                 :            : 
     209                 :            :                 /*
     210                 :            :                  * For single mm user, we can simply issue a memory barrier
     211                 :            :                  * after setting MEMBARRIER_STATE_GLOBAL_EXPEDITED in the
     212                 :            :                  * mm and in the current runqueue to guarantee that no memory
     213                 :            :                  * access following registration is reordered before
     214                 :            :                  * registration.
     215                 :            :                  */
     216                 :          0 :                 smp_mb();
     217                 :          0 :                 return 0;
     218                 :            :         }
     219                 :            : 
     220                 :            :         if (!zalloc_cpumask_var(&tmpmask, GFP_KERNEL))
     221                 :            :                 return -ENOMEM;
     222                 :            : 
     223                 :            :         /*
     224                 :            :          * For mm with multiple users, we need to ensure all future
     225                 :            :          * scheduler executions will observe @mm's new membarrier
     226                 :            :          * state.
     227                 :            :          */
     228                 :          0 :         synchronize_rcu();
     229                 :            : 
     230                 :            :         /*
     231                 :            :          * For each cpu runqueue, if the task's mm match @mm, ensure that all
     232                 :            :          * @mm's membarrier state set bits are also set in in the runqueue's
     233                 :            :          * membarrier state. This ensures that a runqueue scheduling
     234                 :            :          * between threads which are users of @mm has its membarrier state
     235                 :            :          * updated.
     236                 :            :          */
     237                 :            :         cpus_read_lock();
     238                 :            :         rcu_read_lock();
     239         [ #  # ]:          0 :         for_each_online_cpu(cpu) {
     240                 :          0 :                 struct rq *rq = cpu_rq(cpu);
     241                 :            :                 struct task_struct *p;
     242                 :            : 
     243                 :          0 :                 p = rcu_dereference(rq->curr);
     244   [ #  #  #  # ]:          0 :                 if (p && p->mm == mm)
     245                 :            :                         __cpumask_set_cpu(cpu, tmpmask);
     246                 :            :         }
     247                 :            :         rcu_read_unlock();
     248                 :            : 
     249                 :          0 :         preempt_disable();
     250                 :          0 :         smp_call_function_many(tmpmask, ipi_sync_rq_state, mm, 1);
     251                 :          0 :         preempt_enable();
     252                 :            : 
     253                 :            :         free_cpumask_var(tmpmask);
     254                 :            :         cpus_read_unlock();
     255                 :            : 
     256                 :          0 :         return 0;
     257                 :            : }
     258                 :            : 
     259                 :          0 : static int membarrier_register_global_expedited(void)
     260                 :            : {
     261                 :          0 :         struct task_struct *p = current;
     262                 :          0 :         struct mm_struct *mm = p->mm;
     263                 :            :         int ret;
     264                 :            : 
     265         [ #  # ]:          0 :         if (atomic_read(&mm->membarrier_state) &
     266                 :            :             MEMBARRIER_STATE_GLOBAL_EXPEDITED_READY)
     267                 :            :                 return 0;
     268                 :          0 :         atomic_or(MEMBARRIER_STATE_GLOBAL_EXPEDITED, &mm->membarrier_state);
     269                 :          0 :         ret = sync_runqueues_membarrier_state(mm);
     270         [ #  # ]:          0 :         if (ret)
     271                 :            :                 return ret;
     272                 :            :         atomic_or(MEMBARRIER_STATE_GLOBAL_EXPEDITED_READY,
     273                 :            :                   &mm->membarrier_state);
     274                 :            : 
     275                 :          0 :         return 0;
     276                 :            : }
     277                 :            : 
     278                 :          0 : static int membarrier_register_private_expedited(int flags)
     279                 :            : {
     280                 :          0 :         struct task_struct *p = current;
     281                 :          0 :         struct mm_struct *mm = p->mm;
     282                 :            :         int ready_state = MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY,
     283                 :            :             set_state = MEMBARRIER_STATE_PRIVATE_EXPEDITED,
     284                 :            :             ret;
     285                 :            : 
     286         [ #  # ]:          0 :         if (flags & MEMBARRIER_FLAG_SYNC_CORE) {
     287                 :            :                 if (!IS_ENABLED(CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE))
     288                 :            :                         return -EINVAL;
     289                 :            :                 ready_state =
     290                 :            :                         MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY;
     291                 :            :         }
     292                 :            : 
     293                 :            :         /*
     294                 :            :          * We need to consider threads belonging to different thread
     295                 :            :          * groups, which use the same mm. (CLONE_VM but not
     296                 :            :          * CLONE_THREAD).
     297                 :            :          */
     298         [ #  # ]:          0 :         if ((atomic_read(&mm->membarrier_state) & ready_state) == ready_state)
     299                 :            :                 return 0;
     300         [ #  # ]:          0 :         if (flags & MEMBARRIER_FLAG_SYNC_CORE)
     301                 :            :                 set_state |= MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE;
     302                 :          0 :         atomic_or(set_state, &mm->membarrier_state);
     303                 :          0 :         ret = sync_runqueues_membarrier_state(mm);
     304         [ #  # ]:          0 :         if (ret)
     305                 :            :                 return ret;
     306                 :            :         atomic_or(ready_state, &mm->membarrier_state);
     307                 :            : 
     308                 :          0 :         return 0;
     309                 :            : }
     310                 :            : 
     311                 :            : /**
     312                 :            :  * sys_membarrier - issue memory barriers on a set of threads
     313                 :            :  * @cmd:   Takes command values defined in enum membarrier_cmd.
     314                 :            :  * @flags: Currently needs to be 0. For future extensions.
     315                 :            :  *
     316                 :            :  * If this system call is not implemented, -ENOSYS is returned. If the
     317                 :            :  * command specified does not exist, not available on the running
     318                 :            :  * kernel, or if the command argument is invalid, this system call
     319                 :            :  * returns -EINVAL. For a given command, with flags argument set to 0,
     320                 :            :  * if this system call returns -ENOSYS or -EINVAL, it is guaranteed to
     321                 :            :  * always return the same value until reboot. In addition, it can return
     322                 :            :  * -ENOMEM if there is not enough memory available to perform the system
     323                 :            :  * call.
     324                 :            :  *
     325                 :            :  * All memory accesses performed in program order from each targeted thread
     326                 :            :  * is guaranteed to be ordered with respect to sys_membarrier(). If we use
     327                 :            :  * the semantic "barrier()" to represent a compiler barrier forcing memory
     328                 :            :  * accesses to be performed in program order across the barrier, and
     329                 :            :  * smp_mb() to represent explicit memory barriers forcing full memory
     330                 :            :  * ordering across the barrier, we have the following ordering table for
     331                 :            :  * each pair of barrier(), sys_membarrier() and smp_mb():
     332                 :            :  *
     333                 :            :  * The pair ordering is detailed as (O: ordered, X: not ordered):
     334                 :            :  *
     335                 :            :  *                        barrier()   smp_mb() sys_membarrier()
     336                 :            :  *        barrier()          X           X            O
     337                 :            :  *        smp_mb()           X           O            O
     338                 :            :  *        sys_membarrier()   O           O            O
     339                 :            :  */
     340                 :          0 : SYSCALL_DEFINE2(membarrier, int, cmd, int, flags)
     341                 :            : {
     342         [ #  # ]:          0 :         if (unlikely(flags))
     343                 :            :                 return -EINVAL;
     344   [ #  #  #  #  :          0 :         switch (cmd) {
             #  #  #  #  
                      # ]
     345                 :            :         case MEMBARRIER_CMD_QUERY:
     346                 :            :         {
     347                 :            :                 int cmd_mask = MEMBARRIER_CMD_BITMASK;
     348                 :            : 
     349                 :            :                 if (tick_nohz_full_enabled())
     350                 :            :                         cmd_mask &= ~MEMBARRIER_CMD_GLOBAL;
     351                 :            :                 return cmd_mask;
     352                 :            :         }
     353                 :            :         case MEMBARRIER_CMD_GLOBAL:
     354                 :            :                 /* MEMBARRIER_CMD_GLOBAL is not compatible with nohz_full. */
     355                 :            :                 if (tick_nohz_full_enabled())
     356                 :            :                         return -EINVAL;
     357         [ #  # ]:          0 :                 if (num_online_cpus() > 1)
     358                 :          0 :                         synchronize_rcu();
     359                 :            :                 return 0;
     360                 :            :         case MEMBARRIER_CMD_GLOBAL_EXPEDITED:
     361                 :          0 :                 return membarrier_global_expedited();
     362                 :            :         case MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED:
     363                 :          0 :                 return membarrier_register_global_expedited();
     364                 :            :         case MEMBARRIER_CMD_PRIVATE_EXPEDITED:
     365                 :          0 :                 return membarrier_private_expedited(0);
     366                 :            :         case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED:
     367                 :          0 :                 return membarrier_register_private_expedited(0);
     368                 :            :         case MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE:
     369                 :          0 :                 return membarrier_private_expedited(MEMBARRIER_FLAG_SYNC_CORE);
     370                 :            :         case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE:
     371                 :          0 :                 return membarrier_register_private_expedited(MEMBARRIER_FLAG_SYNC_CORE);
     372                 :            :         default:
     373                 :          0 :                 return -EINVAL;
     374                 :            :         }
     375                 :            : }

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