mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-08-27 03:10:12 +00:00
![Mathieu Desnoyers](/assets/img/avatar_default.png)
Userspace applications should be allowed to expect the membarrier system call with MEMBARRIER_CMD_SHARED command to issue memory barriers on nohz_full CPUs, but synchronize_sched() does not take those into account. Given that we do not want unrelated processes to be able to affect real-time sensitive nohz_full CPUs, simply return ENOSYS when membarrier is invoked on a kernel with enabled nohz_full CPUs. Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> CC: Josh Triplett <josh@joshtriplett.org> CC: Steven Rostedt <rostedt@goodmis.org> CC: <stable@vger.kernel.org> [3.10+] Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Chris Metcalf <cmetcalf@mellanox.com> Cc: Rik van Riel <riel@redhat.com> Acked-by: Lai Jiangshan <jiangshanlai@gmail.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
70 lines
2.5 KiB
C
70 lines
2.5 KiB
C
/*
|
|
* Copyright (C) 2010, 2015 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>
|
|
|
|
/*
|
|
* 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;
|
|
}
|
|
}
|