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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>
This commit is contained in:
Mathieu Desnoyers 2016-11-03 10:29:28 -06:00 committed by Paul E. McKenney
parent 4d4f88fa23
commit 907565337e
1 changed files with 4 additions and 0 deletions
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4
kernel/membarrier.c
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@ -16,6 +16,7 @@
#include <linux/syscalls.h> #include <linux/syscalls.h>
#include <linux/membarrier.h> #include <linux/membarrier.h>
#include <linux/tick.h>
/* /*
* Bitmask made from a "or" of all commands within enum membarrier_cmd, * Bitmask made from a "or" of all commands within enum membarrier_cmd,
@ -51,6 +52,9 @@
*/ */
SYSCALL_DEFINE2(membarrier, int, cmd, int, flags) 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)) if (unlikely(flags))
return -EINVAL; return -EINVAL;
switch (cmd) { switch (cmd) {