4.9-stable review patch. If anyone has any objections, please let me know.
------------------
From: Mathieu Desnoyers <mathieu.desnoy...@efficios.com>
commit 907565337ebf998a68cb5c5b2174ce5e5da065eb upstream.
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.desnoy...@efficios.com>
CC: Josh Triplett <j...@joshtriplett.org>
CC: Steven Rostedt <rost...@goodmis.org>
Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweis...@gmail.com>
Cc: Chris Metcalf <cmetc...@mellanox.com>
Cc: Rik van Riel <r...@redhat.com>
Acked-by: Lai Jiangshan <jiangshan...@gmail.com>
Reviewed-by: Josh Triplett <j...@joshtriplett.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
kernel/membarrier.c | 4 ++++
1 file changed, 4 insertions(+)
--- 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) {
