319 lines
9.3 KiB
C
319 lines
9.3 KiB
C
/*
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* Copyright (C) 2010-2017 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
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*
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* membarrier system call
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*/
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#include "sched.h"
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/*
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* Bitmask made from a "or" of all commands within enum membarrier_cmd,
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* except MEMBARRIER_CMD_QUERY.
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*/
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#ifdef CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE
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#define MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK \
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(MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE \
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| MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE)
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#else
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#define MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK 0
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#endif
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#define MEMBARRIER_CMD_BITMASK \
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(MEMBARRIER_CMD_GLOBAL | MEMBARRIER_CMD_GLOBAL_EXPEDITED \
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| MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED \
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| MEMBARRIER_CMD_PRIVATE_EXPEDITED \
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| MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED \
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| MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK)
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static void ipi_mb(void *info)
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{
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smp_mb(); /* IPIs should be serializing but paranoid. */
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}
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static int membarrier_global_expedited(void)
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{
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int cpu;
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bool fallback = false;
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cpumask_var_t tmpmask;
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if (num_online_cpus() == 1)
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return 0;
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/*
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* Matches memory barriers around rq->curr modification in
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* scheduler.
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*/
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smp_mb(); /* system call entry is not a mb. */
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/*
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* Expedited membarrier commands guarantee that they won't
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* block, hence the GFP_NOWAIT allocation flag and fallback
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* implementation.
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*/
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if (!zalloc_cpumask_var(&tmpmask, GFP_NOWAIT)) {
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/* Fallback for OOM. */
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fallback = true;
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}
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cpus_read_lock();
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for_each_online_cpu(cpu) {
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struct task_struct *p;
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/*
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* Skipping the current CPU is OK even through we can be
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* migrated at any point. The current CPU, at the point
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* where we read raw_smp_processor_id(), is ensured to
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* be in program order with respect to the caller
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* thread. Therefore, we can skip this CPU from the
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* iteration.
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*/
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if (cpu == raw_smp_processor_id())
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continue;
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rcu_read_lock();
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p = task_rcu_dereference(&cpu_rq(cpu)->curr);
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if (p && p->mm && (atomic_read(&p->mm->membarrier_state) &
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MEMBARRIER_STATE_GLOBAL_EXPEDITED)) {
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if (!fallback)
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__cpumask_set_cpu(cpu, tmpmask);
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else
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smp_call_function_single(cpu, ipi_mb, NULL, 1);
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}
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rcu_read_unlock();
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}
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if (!fallback) {
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preempt_disable();
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smp_call_function_many(tmpmask, ipi_mb, NULL, 1);
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preempt_enable();
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free_cpumask_var(tmpmask);
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}
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cpus_read_unlock();
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/*
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* Memory barrier on the caller thread _after_ we finished
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* waiting for the last IPI. Matches memory barriers around
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* rq->curr modification in scheduler.
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*/
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smp_mb(); /* exit from system call is not a mb */
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return 0;
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}
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static int membarrier_private_expedited(int flags)
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{
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int cpu;
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bool fallback = false;
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cpumask_var_t tmpmask;
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if (flags & MEMBARRIER_FLAG_SYNC_CORE) {
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if (!IS_ENABLED(CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE))
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return -EINVAL;
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if (!(atomic_read(¤t->mm->membarrier_state) &
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MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY))
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return -EPERM;
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} else {
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if (!(atomic_read(¤t->mm->membarrier_state) &
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MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY))
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return -EPERM;
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}
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if (num_online_cpus() == 1)
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return 0;
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/*
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* Matches memory barriers around rq->curr modification in
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* scheduler.
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*/
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smp_mb(); /* system call entry is not a mb. */
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/*
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* Expedited membarrier commands guarantee that they won't
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* block, hence the GFP_NOWAIT allocation flag and fallback
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* implementation.
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*/
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if (!zalloc_cpumask_var(&tmpmask, GFP_NOWAIT)) {
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/* Fallback for OOM. */
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fallback = true;
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}
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cpus_read_lock();
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for_each_online_cpu(cpu) {
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struct task_struct *p;
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/*
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* Skipping the current CPU is OK even through we can be
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* migrated at any point. The current CPU, at the point
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* where we read raw_smp_processor_id(), is ensured to
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* be in program order with respect to the caller
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* thread. Therefore, we can skip this CPU from the
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* iteration.
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*/
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if (cpu == raw_smp_processor_id())
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continue;
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rcu_read_lock();
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p = task_rcu_dereference(&cpu_rq(cpu)->curr);
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if (p && p->mm == current->mm) {
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if (!fallback)
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__cpumask_set_cpu(cpu, tmpmask);
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else
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smp_call_function_single(cpu, ipi_mb, NULL, 1);
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}
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rcu_read_unlock();
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}
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if (!fallback) {
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preempt_disable();
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smp_call_function_many(tmpmask, ipi_mb, NULL, 1);
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preempt_enable();
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free_cpumask_var(tmpmask);
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}
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cpus_read_unlock();
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/*
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* Memory barrier on the caller thread _after_ we finished
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* waiting for the last IPI. Matches memory barriers around
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* rq->curr modification in scheduler.
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*/
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smp_mb(); /* exit from system call is not a mb */
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return 0;
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}
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static int membarrier_register_global_expedited(void)
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{
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struct task_struct *p = current;
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struct mm_struct *mm = p->mm;
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if (atomic_read(&mm->membarrier_state) &
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MEMBARRIER_STATE_GLOBAL_EXPEDITED_READY)
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return 0;
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atomic_or(MEMBARRIER_STATE_GLOBAL_EXPEDITED, &mm->membarrier_state);
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if (atomic_read(&mm->mm_users) == 1 && get_nr_threads(p) == 1) {
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/*
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* For single mm user, single threaded process, we can
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* simply issue a memory barrier after setting
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* MEMBARRIER_STATE_GLOBAL_EXPEDITED to guarantee that
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* no memory access following registration is reordered
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* before registration.
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*/
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smp_mb();
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} else {
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/*
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* For multi-mm user threads, we need to ensure all
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* future scheduler executions will observe the new
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* thread flag state for this mm.
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*/
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synchronize_rcu();
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}
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atomic_or(MEMBARRIER_STATE_GLOBAL_EXPEDITED_READY,
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&mm->membarrier_state);
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return 0;
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}
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static int membarrier_register_private_expedited(int flags)
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{
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struct task_struct *p = current;
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struct mm_struct *mm = p->mm;
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int state = MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY;
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if (flags & MEMBARRIER_FLAG_SYNC_CORE) {
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if (!IS_ENABLED(CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE))
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return -EINVAL;
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state = MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY;
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}
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/*
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* We need to consider threads belonging to different thread
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* groups, which use the same mm. (CLONE_VM but not
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* CLONE_THREAD).
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*/
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if (atomic_read(&mm->membarrier_state) & state)
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return 0;
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atomic_or(MEMBARRIER_STATE_PRIVATE_EXPEDITED, &mm->membarrier_state);
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if (flags & MEMBARRIER_FLAG_SYNC_CORE)
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atomic_or(MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE,
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&mm->membarrier_state);
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if (!(atomic_read(&mm->mm_users) == 1 && get_nr_threads(p) == 1)) {
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/*
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* Ensure all future scheduler executions will observe the
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* new thread flag state for this process.
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*/
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synchronize_rcu();
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}
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atomic_or(state, &mm->membarrier_state);
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return 0;
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}
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/**
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* sys_membarrier - issue memory barriers on a set of threads
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* @cmd: Takes command values defined in enum membarrier_cmd.
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* @flags: Currently needs to be 0. For future extensions.
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*
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* If this system call is not implemented, -ENOSYS is returned. If the
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* command specified does not exist, not available on the running
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* kernel, or if the command argument is invalid, this system call
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* returns -EINVAL. For a given command, with flags argument set to 0,
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* this system call is guaranteed to always return the same value until
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* reboot.
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*
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* All memory accesses performed in program order from each targeted thread
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* is guaranteed to be ordered with respect to sys_membarrier(). If we use
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* the semantic "barrier()" to represent a compiler barrier forcing memory
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* accesses to be performed in program order across the barrier, and
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* smp_mb() to represent explicit memory barriers forcing full memory
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* ordering across the barrier, we have the following ordering table for
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* each pair of barrier(), sys_membarrier() and smp_mb():
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*
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* The pair ordering is detailed as (O: ordered, X: not ordered):
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*
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* barrier() smp_mb() sys_membarrier()
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* barrier() X X O
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* smp_mb() X O O
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* sys_membarrier() O O O
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*/
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SYSCALL_DEFINE2(membarrier, int, cmd, int, flags)
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{
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if (unlikely(flags))
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return -EINVAL;
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switch (cmd) {
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case MEMBARRIER_CMD_QUERY:
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{
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int cmd_mask = MEMBARRIER_CMD_BITMASK;
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if (tick_nohz_full_enabled())
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cmd_mask &= ~MEMBARRIER_CMD_GLOBAL;
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return cmd_mask;
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}
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case MEMBARRIER_CMD_GLOBAL:
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/* MEMBARRIER_CMD_GLOBAL is not compatible with nohz_full. */
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if (tick_nohz_full_enabled())
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return -EINVAL;
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if (num_online_cpus() > 1)
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synchronize_rcu();
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return 0;
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case MEMBARRIER_CMD_GLOBAL_EXPEDITED:
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return membarrier_global_expedited();
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case MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED:
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return membarrier_register_global_expedited();
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case MEMBARRIER_CMD_PRIVATE_EXPEDITED:
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return membarrier_private_expedited(0);
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case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED:
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return membarrier_register_private_expedited(0);
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case MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE:
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return membarrier_private_expedited(MEMBARRIER_FLAG_SYNC_CORE);
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case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE:
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return membarrier_register_private_expedited(MEMBARRIER_FLAG_SYNC_CORE);
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default:
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return -EINVAL;
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}
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}
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