Patch "Fix: Disable sys_membarrier when nohz_full is enabled" has been added to the 4.10-stable tree

This is a note to let you know that I've just added the patch titled

Fix: Disable sys_membarrier when nohz_full is enabled

to the 4.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
fix-disable-sys_membarrier-when-nohz_full-is-enabled.patch
and it can be found in the queue-4.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Mathieu Desnoyers <[email protected]>
Date: Thu, 3 Nov 2016 10:29:28 -0600
Subject: Fix: Disable sys_membarrier when nohz_full is enabled

From: Mathieu Desnoyers <[email protected]>

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.

---
 kernel/membarrier.c |    4 ++++
 1 file changed, 4 insertions(+)

@@ -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) {

Patches currently in stable-queue which might be from [email protected] are

queue-4.10/fix-disable-sys_membarrier-when-nohz_full-is-enabled.patch