Fix: Disable sys_membarrier when nohz_full is enabled
authorMathieu Desnoyers <mathieu.desnoyers@efficios.com>
Thu, 3 Nov 2016 16:29:28 +0000 (10:29 -0600)
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Mon, 23 Jan 2017 19:32:16 +0000 (11:32 -0800)
commit907565337ebf998a68cb5c5b2174ce5e5da065eb
tree5e5e3a5e43b3755f906bbc26bd20da6dd1dbe878
parent4d4f88fa235f7f9ef8213564dc1804144332238b
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>
kernel/membarrier.c