forked from Minki/linux
70216e18e5
Provide core serializing membarrier command to support memory reclaim by JIT. Each architecture needs to explicitly opt into that support by documenting in their architecture code how they provide the core serializing instructions required when returning from the membarrier IPI, and after the scheduler has updated the curr->mm pointer (before going back to user-space). They should then select ARCH_HAS_MEMBARRIER_SYNC_CORE to enable support for that command on their architecture. Architectures selecting this feature need to either document that they issue core serializing instructions when returning to user-space, or implement their architecture-specific sync_core_before_usermode(). Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Acked-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Andrea Parri <parri.andrea@gmail.com> Cc: Andrew Hunter <ahh@google.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Avi Kivity <avi@scylladb.com> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Boqun Feng <boqun.feng@gmail.com> Cc: Dave Watson <davejwatson@fb.com> Cc: David Sehr <sehr@google.com> Cc: Greg Hackmann <ghackmann@google.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Maged Michael <maged.michael@gmail.com> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Paul Mackerras <paulus@samba.org> Cc: Russell King <linux@armlinux.org.uk> Cc: Will Deacon <will.deacon@arm.com> Cc: linux-api@vger.kernel.org Cc: linux-arch@vger.kernel.org Link: http://lkml.kernel.org/r/20180129202020.8515-9-mathieu.desnoyers@efficios.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
322 lines
9.4 KiB
C
322 lines
9.4 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 <linux/syscalls.h>
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#include <linux/membarrier.h>
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#include <linux/tick.h>
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#include <linux/cpumask.h>
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#include <linux/atomic.h>
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#include "sched.h" /* for cpu_rq(). */
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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_sched();
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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_sched();
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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_sched();
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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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