Commit 90756533 authored Nov 03, 2016 by Mathieu Desnoyers Committed by Paul E. McKenney Jan 23, 2017

Fix: Disable sys_membarrier when nohz_full is enabled



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>

parent 4d4f88fa

kernel/membarrier.c

+4 −0

Original line number	Diff line number	Diff line
		@@ -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) {

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