From: Mathieu Desnoyers <mathieu.desnoy...@efficios.com> 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> CC: <sta...@vger.kernel.org> [3.10+] 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> --- kernel/membarrier.c | 4 ++++ 1 file changed, 4 insertions(+) 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) { -- 2.5.2