mirror of https://github.com/Qortal/Brooklyn
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
70 lines
2.5 KiB
70 lines
2.5 KiB
/* |
|
* Copyright (C) 2010, 2015 Mathieu Desnoyers <[email protected]> |
|
* |
|
* 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> |
|
|
|
/* |
|
* Bitmask made from a "or" of all commands within enum membarrier_cmd, |
|
* except MEMBARRIER_CMD_QUERY. |
|
*/ |
|
#define MEMBARRIER_CMD_BITMASK (MEMBARRIER_CMD_SHARED) |
|
|
|
/** |
|
* 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, 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) |
|
{ |
|
/* MEMBARRIER_CMD_SHARED is not compatible with nohz_full. */ |
|
if (tick_nohz_full_enabled()) |
|
return -ENOSYS; |
|
if (unlikely(flags)) |
|
return -EINVAL; |
|
switch (cmd) { |
|
case MEMBARRIER_CMD_QUERY: |
|
return MEMBARRIER_CMD_BITMASK; |
|
case MEMBARRIER_CMD_SHARED: |
|
if (num_online_cpus() > 1) |
|
synchronize_sched(); |
|
return 0; |
|
default: |
|
return -EINVAL; |
|
} |
|
}
|
|
|