From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: linux-kernel@vger.kernel.org,
Josh Triplett <josh@joshtriplett.org>,
Steven Rostedt <rostedt@goodmis.org>,
Lai Jiangshan <jiangshanlai@gmail.com>,
stable@vger.kernel.org
Subject: Re: [PATCH] Fix: disable sys_membarrier when nohz_full is enabled
Date: Thu, 3 Nov 2016 10:49:11 -0700 [thread overview]
Message-ID: <20161103174911.GL3716@linux.vnet.ibm.com> (raw)
In-Reply-To: <1478190568-5829-1-git-send-email-mathieu.desnoyers@efficios.com>
On Thu, Nov 03, 2016 at 10:29:28AM -0600, Mathieu Desnoyers wrote:
> 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: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Acked-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
> CC: Josh Triplett <josh@joshtriplett.org>
> CC: Steven Rostedt <rostedt@goodmis.org>
> CC: Lai Jiangshan <jiangshanlai@gmail.com>
> CC: <stable@vger.kernel.org> [3.10+]
> ---
> kernel/membarrier.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/kernel/membarrier.c b/kernel/membarrier.c
> index 536c727..9f9284f 100644
> --- a/kernel/membarrier.c
> +++ b/kernel/membarrier.c
> @@ -16,6 +16,7 @@
>
> #include <linux/syscalls.h>
> #include <linux/membarrier.h>
> +#include <linux/tick.h>
>
> /*
> * Bitmask made from a "or" of all commands within enum membarrier_cmd,
> @@ -51,6 +52,9 @@
> */
> 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) {
> --
> 2.1.4
>
next prev parent reply other threads:[~2016-11-03 17:49 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-03 16:29 [PATCH] Fix: disable sys_membarrier when nohz_full is enabled Mathieu Desnoyers
2016-11-03 17:49 ` Paul E. McKenney [this message]
2016-11-07 17:08 ` Mathieu Desnoyers
2016-11-07 18:06 ` Paul E. McKenney
2016-11-07 18:10 ` Mathieu Desnoyers
2016-11-07 20:03 ` Paul E. McKenney
2016-11-08 11:15 ` Mathieu Desnoyers
2016-11-12 17:58 ` Paul E. McKenney
2016-11-17 6:51 ` Lai Jiangshan
2016-11-17 11:46 ` Mathieu Desnoyers
2016-11-17 13:40 ` Paul E. McKenney
2016-11-17 13:54 ` Mathieu Desnoyers
2016-11-17 14:09 ` Paul E. McKenney
2016-11-17 14:50 ` Steven Rostedt
2016-11-17 15:02 ` Mathieu Desnoyers
2016-11-17 15:17 ` Steven Rostedt
2016-11-17 16:02 ` Paul E. McKenney
2016-11-17 13:38 ` Paul E. McKenney
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