diff --git a/MAINTAINERS b/MAINTAINERS
index 310da4295c7026e27698e9f8b980adcc1893b774..e77bc84dc580bd4635e96b91194a3f0adb2693ab 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -6789,6 +6789,14 @@ W: http://www.mellanox.com
Q: http://patchwork.ozlabs.org/project/netdev/list/
F: drivers/net/ethernet/mellanox/mlxsw/
+MEMBARRIER SUPPORT
+M: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+M: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
+L: linux-kernel@vger.kernel.org
+S: Supported
+F: kernel/membarrier.c
+F: include/uapi/linux/membarrier.h
+
MEMORY MANAGEMENT
L: linux-mm@kvack.org
W: http://www.linux-mm.org
diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index 477bfa6db370783294e858210a8064b295da3082..7663c455b9f650f67292e5a2c4664606fb1dbacb 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -381,3 +381,4 @@
372 i386 recvmsg sys_recvmsg compat_sys_recvmsg
373 i386 shutdown sys_shutdown
374 i386 userfaultfd sys_userfaultfd
+375 i386 membarrier sys_membarrier
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index 81c490634db994ba810984f8f6dab052a54c8139..278842fdf1f6393d58ea0ac09abe60ef09e8ce79 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -330,6 +330,7 @@
321 common bpf sys_bpf
322 64 execveat stub_execveat
323 common userfaultfd sys_userfaultfd
+324 common membarrier sys_membarrier
#
# x32-specific system call numbers start at 512 to avoid cache impact
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 08001317aee7376babb542aa9bb15936d38ef533..a460e2ef28437237d2b4bc2d09486b794290f21d 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -885,4 +885,6 @@ asmlinkage long sys_execveat(int dfd, const char __user *filename,
const char __user *const __user *argv,
const char __user *const __user *envp, int flags);
+asmlinkage long sys_membarrier(int cmd, int flags);
+
#endif
diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
index e016bd9b1a049686da0ee465fd561a8062156ff6..8da542a2874d6c3490860eec0092ac26998a303d 100644
--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h
@@ -709,9 +709,11 @@ __SYSCALL(__NR_memfd_create, sys_memfd_create)
__SYSCALL(__NR_bpf, sys_bpf)
#define __NR_execveat 281
__SC_COMP(__NR_execveat, sys_execveat, compat_sys_execveat)
+#define __NR_membarrier 282
+__SYSCALL(__NR_membarrier, sys_membarrier)
#undef __NR_syscalls
-#define __NR_syscalls 282
+#define __NR_syscalls 283
/*
* All syscalls below here should go away really,
diff --git a/include/uapi/linux/Kbuild b/include/uapi/linux/Kbuild
index 70ff1d9abf0ddab0055d64b1d9ec70b8f488fd9f..f7b2db44eb4b07a910d0097e63a657c1e4a37816 100644
--- a/include/uapi/linux/Kbuild
+++ b/include/uapi/linux/Kbuild
@@ -252,6 +252,7 @@ header-y += mdio.h
header-y += media.h
header-y += media-bus-format.h
header-y += mei.h
+header-y += membarrier.h
header-y += memfd.h
header-y += mempolicy.h
header-y += meye.h
diff --git a/include/uapi/linux/membarrier.h b/include/uapi/linux/membarrier.h
new file mode 100644
index 0000000000000000000000000000000000000000..e0b108bd2624de3765538fe61f5c2852ca766593
--- /dev/null
+++ b/include/uapi/linux/membarrier.h
@@ -0,0 +1,53 @@
+#ifndef _UAPI_LINUX_MEMBARRIER_H
+#define _UAPI_LINUX_MEMBARRIER_H
+
+/*
+ * linux/membarrier.h
+ *
+ * membarrier system call API
+ *
+ * Copyright (c) 2010, 2015 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+/**
+ * enum membarrier_cmd - membarrier system call command
+ * @MEMBARRIER_CMD_QUERY: Query the set of supported commands. It returns
+ * a bitmask of valid commands.
+ * @MEMBARRIER_CMD_SHARED: Execute a memory barrier on all running threads.
+ * Upon return from system call, the caller thread
+ * is ensured that all running threads have passed
+ * through a state where all memory accesses to
+ * user-space addresses match program order between
+ * entry to and return from the system call
+ * (non-running threads are de facto in such a
+ * state). This covers threads from all processes
+ * running on the system. This command returns 0.
+ *
+ * Command to be passed to the membarrier system call. The commands need to
+ * be a single bit each, except for MEMBARRIER_CMD_QUERY which is assigned to
+ * the value 0.
+ */
+enum membarrier_cmd {
+ MEMBARRIER_CMD_QUERY = 0,
+ MEMBARRIER_CMD_SHARED = (1 << 0),
+};
+
+#endif /* _UAPI_LINUX_MEMBARRIER_H */
diff --git a/init/Kconfig b/init/Kconfig
index 02da9f1fd9df16ee1e6c6bdcf5cbc8c2e05c52d5..c24b6f767bf0f2a4d8a873388a5fbd59ba01c562 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1602,6 +1602,18 @@ config PCI_QUIRKS
bugs/quirks. Disable this only if your target machine is
unaffected by PCI quirks.
+config MEMBARRIER
+ bool "Enable membarrier() system call" if EXPERT
+ default y
+ help
+ Enable the membarrier() system call that allows issuing memory
+ barriers across all running threads, which can be used to distribute
+ the cost of user-space memory barriers asymmetrically by transforming
+ pairs of memory barriers into pairs consisting of membarrier() and a
+ compiler barrier.
+
+ If unsure, say Y.
+
config EMBEDDED
bool "Embedded system"
option allnoconfig_y
diff --git a/kernel/Makefile b/kernel/Makefile
index d4988410b410a6ae802b5d796b99e73d80393dc1..53abf008ecb39758e1812f7a593323d65e7fd304 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -100,6 +100,7 @@ obj-$(CONFIG_CRASH_DUMP) += crash_dump.o
obj-$(CONFIG_JUMP_LABEL) += jump_label.o
obj-$(CONFIG_CONTEXT_TRACKING) += context_tracking.o
obj-$(CONFIG_TORTURE_TEST) += torture.o
+obj-$(CONFIG_MEMBARRIER) += membarrier.o
obj-$(CONFIG_HAS_IOMEM) += memremap.o
diff --git a/kernel/membarrier.c b/kernel/membarrier.c
new file mode 100644
index 0000000000000000000000000000000000000000..536c727a56e975e2e310fb3fb82474f07a1b916f
--- /dev/null
+++ b/kernel/membarrier.c
@@ -0,0 +1,66 @@
+/*
+ * Copyright (C) 2010, 2015 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ *
+ * membarrier system call
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ */
+
+#include <linux/syscalls.h>
+#include <linux/membarrier.h>
+
+/*
+ * Bitmask made from a "or" of all commands within enum membarrier_cmd,
+ * except MEMBARRIER_CMD_QUERY.
+ */
+#define MEMBARRIER_CMD_BITMASK (MEMBARRIER_CMD_SHARED)
+
+/**
+ * sys_membarrier - issue memory barriers on a set of threads
+ * @cmd: Takes command values defined in enum membarrier_cmd.
+ * @flags: Currently needs to be 0. For future extensions.
+ *
+ * If this system call is not implemented, -ENOSYS is returned. If the
+ * command specified does not exist, or if the command argument is invalid,
+ * this system call returns -EINVAL. For a given command, with flags argument
+ * set to 0, this system call is guaranteed to always return the same value
+ * until reboot.
+ *
+ * All memory accesses performed in program order from each targeted thread
+ * is guaranteed to be ordered with respect to sys_membarrier(). If we use
+ * the semantic "barrier()" to represent a compiler barrier forcing memory
+ * accesses to be performed in program order across the barrier, and
+ * smp_mb() to represent explicit memory barriers forcing full memory
+ * ordering across the barrier, we have the following ordering table for
+ * each pair of barrier(), sys_membarrier() and smp_mb():
+ *
+ * The pair ordering is detailed as (O: ordered, X: not ordered):
+ *
+ * barrier() smp_mb() sys_membarrier()
+ * barrier() X X O
+ * smp_mb() X O O
+ * sys_membarrier() O O O
+ */
+SYSCALL_DEFINE2(membarrier, int, cmd, int, flags)
+{
+ if (unlikely(flags))
+ return -EINVAL;
+ switch (cmd) {
+ case MEMBARRIER_CMD_QUERY:
+ return MEMBARRIER_CMD_BITMASK;
+ case MEMBARRIER_CMD_SHARED:
+ if (num_online_cpus() > 1)
+ synchronize_sched();
+ return 0;
+ default:
+ return -EINVAL;
+ }
+}
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index 03c3875d995898b2af39ac593379085cb250c242..a02decf155832fa03117ce6e6ebf89e6a0b2809f 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -245,3 +245,6 @@ cond_syscall(sys_bpf);
/* execveat */
cond_syscall(sys_execveat);
+
+/* membarrier */
+cond_syscall(sys_membarrier);