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