| From | "Paul E. McKenney" <> | Subject | [PATCH v2 tip/core/rcu 03/18] Fix: Disable sys_membarrier when nohz_full is enabled | Date | Tue, 17 Jan 2017 18:53:42 -0800 |
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From: Mathieu Desnoyers <mathieu.desnoyers@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.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> --- 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
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