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authorMathieu Desnoyers <mathieu.desnoyers@efficios.com>2016-11-03 10:29:28 -0600
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2017-03-12 06:37:26 +0100
commitc0ef1f537a9728a91475f8f73cf8b5764e7a9848 (patch)
tree5c13f17f5ab5b26fdeda83ceaefdc91859e93eaa
parentea240cfed99bda8fc1774801cb9da355e66dc7e1 (diff)
downloadlinux-linaro-stable-c0ef1f537a9728a91475f8f73cf8b5764e7a9848.tar.gz
Fix: Disable sys_membarrier when nohz_full is enabled
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.desnoyers@efficios.com> CC: Josh Triplett <josh@joshtriplett.org> CC: Steven Rostedt <rostedt@goodmis.org> 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> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--kernel/membarrier.c4
1 files changed, 4 insertions, 0 deletions
diff --git a/kernel/membarrier.c b/kernel/membarrier.c
index 536c727a56e9..9f9284f37f8d 100644
--- 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) {