Merge branch 'akpm' (patches from Andrew)

Merge fourth patch-bomb from Andrew Morton:

 - sys_membarier syscall

 - seq_file interface changes

 - a few misc fixups

* emailed patches from Andrew Morton <akpm@linux-foundation.org>:
  revert "ocfs2/dlm: use list_for_each_entry instead of list_for_each"
  mm/early_ioremap: add explicit #include of asm/early_ioremap.h
  fs/seq_file: convert int seq_vprint/seq_printf/etc... returns to void
  selftests: enhance membarrier syscall test
  selftests: add membarrier syscall test
  sys_membarrier(): system-wide memory barrier (generic, x86)
  MODSIGN: fix a compilation warning in extract-cert

22 files changed, 336 insertions, 54 deletions

diff --git a/MAINTAINERS b/MAINTAINERS
index 030d8724b476..7ba7ab749c85 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 477bfa6db370..7663c455b9f6 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 81c490634db9..278842fdf1f6 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/drivers/iommu/omap-iommu-debug.c b/drivers/iommu/omap-iommu-debug.c
index 0717aa96ce39..9bc20e2119a3 100644
--- a/drivers/iommu/omap-iommu-debug.c
+++ b/drivers/iommu/omap-iommu-debug.c
@@ -135,8 +135,9 @@ __dump_tlb_entries(struct omap_iommu *obj, struct cr_regs *crs, int num)
 static ssize_t iotlb_dump_cr(struct omap_iommu *obj, struct cr_regs *cr,
 			     struct seq_file *s)
 {
-	return seq_printf(s, "%08x %08x %01x\n", cr->cam, cr->ram,
+	seq_printf(s, "%08x %08x %01x\n", cr->cam, cr->ram,
 			  (cr->cam & MMU_CAM_P) ? 1 : 0);
+	return 0;
 }
 
 static size_t omap_dump_tlb_entries(struct omap_iommu *obj, struct seq_file *s)
diff --git a/fs/nsfs.c b/fs/nsfs.c
index e4905fbf3396..8f20d6016e20 100644
--- a/fs/nsfs.c
+++ b/fs/nsfs.c
@@ -142,7 +142,8 @@ static int nsfs_show_path(struct seq_file *seq, struct dentry *dentry)
 	struct inode *inode = d_inode(dentry);
 	const struct proc_ns_operations *ns_ops = dentry->d_fsdata;
 
-	return seq_printf(seq, "%s:[%lu]", ns_ops->name, inode->i_ino);
+	seq_printf(seq, "%s:[%lu]", ns_ops->name, inode->i_ino);
+	return 0;
 }
 
 static const struct super_operations nsfs_ops = {
diff --git a/fs/ocfs2/dlm/dlmrecovery.c b/fs/ocfs2/dlm/dlmrecovery.c
index d0e436dc6437..ce12e0b1a31f 100644
--- a/fs/ocfs2/dlm/dlmrecovery.c
+++ b/fs/ocfs2/dlm/dlmrecovery.c
@@ -1776,7 +1776,7 @@ static int dlm_process_recovery_data(struct dlm_ctxt *dlm,
 				     struct dlm_migratable_lockres *mres)
 {
 	struct dlm_migratable_lock *ml;
-	struct list_head *queue;
+	struct list_head *queue, *iter;
 	struct list_head *tmpq = NULL;
 	struct dlm_lock *newlock = NULL;
 	struct dlm_lockstatus *lksb = NULL;
@@ -1821,7 +1821,9 @@ static int dlm_process_recovery_data(struct dlm_ctxt *dlm,
 			spin_lock(&res->spinlock);
 			for (j = DLM_GRANTED_LIST; j <= DLM_BLOCKED_LIST; j++) {
 				tmpq = dlm_list_idx_to_ptr(res, j);
-				list_for_each_entry(lock, tmpq, list) {
+				list_for_each(iter, tmpq) {
+					lock = list_entry(iter,
+						  struct dlm_lock, list);
 					if (lock->ml.cookie == ml->cookie)
 						break;
 					lock = NULL;
diff --git a/fs/seq_file.c b/fs/seq_file.c
index 263b125dbcf4..225586e141ca 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -372,16 +372,16 @@ EXPORT_SYMBOL(seq_release);
  *	@esc:	set of characters that need escaping
  *
  *	Puts string into buffer, replacing each occurrence of character from
- *	@esc with usual octal escape.  Returns 0 in case of success, -1 - in
- *	case of overflow.
+ *	@esc with usual octal escape.
+ *	Use seq_has_overflowed() to check for errors.
  */
-int seq_escape(struct seq_file *m, const char *s, const char *esc)
+void seq_escape(struct seq_file *m, const char *s, const char *esc)
 {
 	char *end = m->buf + m->size;
-        char *p;
+	char *p;
 	char c;
 
-        for (p = m->buf + m->count; (c = *s) != '\0' && p < end; s++) {
+	for (p = m->buf + m->count; (c = *s) != '\0' && p < end; s++) {
 		if (!strchr(esc, c)) {
 			*p++ = c;
 			continue;
@@ -394,14 +394,13 @@ int seq_escape(struct seq_file *m, const char *s, const char *esc)
 			continue;
 		}
 		seq_set_overflow(m);
-		return -1;
-        }
+		return;
+	}
 	m->count = p - m->buf;
-        return 0;
 }
 EXPORT_SYMBOL(seq_escape);
 
-int seq_vprintf(struct seq_file *m, const char *f, va_list args)
+void seq_vprintf(struct seq_file *m, const char *f, va_list args)
 {
 	int len;
 
@@ -409,24 +408,20 @@ int seq_vprintf(struct seq_file *m, const char *f, va_list args)
 		len = vsnprintf(m->buf + m->count, m->size - m->count, f, args);
 		if (m->count + len < m->size) {
 			m->count += len;
-			return 0;
+			return;
 		}
 	}
 	seq_set_overflow(m);
-	return -1;
 }
 EXPORT_SYMBOL(seq_vprintf);
 
-int seq_printf(struct seq_file *m, const char *f, ...)
+void seq_printf(struct seq_file *m, const char *f, ...)
 {
-	int ret;
 	va_list args;
 
 	va_start(args, f);
-	ret = seq_vprintf(m, f, args);
+	seq_vprintf(m, f, args);
 	va_end(args);
-
-	return ret;
 }
 EXPORT_SYMBOL(seq_printf);
 
@@ -664,26 +659,25 @@ int seq_open_private(struct file *filp, const struct seq_operations *ops,
 }
 EXPORT_SYMBOL(seq_open_private);
 
-int seq_putc(struct seq_file *m, char c)
+void seq_putc(struct seq_file *m, char c)
 {
-	if (m->count < m->size) {
-		m->buf[m->count++] = c;
-		return 0;
-	}
-	return -1;
+	if (m->count >= m->size)
+		return;
+
+	m->buf[m->count++] = c;
 }
 EXPORT_SYMBOL(seq_putc);
 
-int seq_puts(struct seq_file *m, const char *s)
+void seq_puts(struct seq_file *m, const char *s)
 {
 	int len = strlen(s);
-	if (m->count + len < m->size) {
-		memcpy(m->buf + m->count, s, len);
-		m->count += len;
-		return 0;
+
+	if (m->count + len >= m->size) {
+		seq_set_overflow(m);
+		return;
 	}
-	seq_set_overflow(m);
-	return -1;
+	memcpy(m->buf + m->count, s, len);
+	m->count += len;
 }
 EXPORT_SYMBOL(seq_puts);
 
@@ -694,8 +688,8 @@ EXPORT_SYMBOL(seq_puts);
  * This routine is very quick when you show lots of numbers.
  * In usual cases, it will be better to use seq_printf(). It's easier to read.
  */
-int seq_put_decimal_ull(struct seq_file *m, char delimiter,
-			unsigned long long num)
+void seq_put_decimal_ull(struct seq_file *m, char delimiter,
+			 unsigned long long num)
 {
 	int len;
 
@@ -707,35 +701,33 @@ int seq_put_decimal_ull(struct seq_file *m, char delimiter,
 
 	if (num < 10) {
 		m->buf[m->count++] = num + '0';
-		return 0;
+		return;
 	}
 
 	len = num_to_str(m->buf + m->count, m->size - m->count, num);
 	if (!len)
 		goto overflow;
 	m->count += len;
-	return 0;
+	return;
+
 overflow:
 	seq_set_overflow(m);
-	return -1;
 }
 EXPORT_SYMBOL(seq_put_decimal_ull);
 
-int seq_put_decimal_ll(struct seq_file *m, char delimiter,
-			long long num)
+void seq_put_decimal_ll(struct seq_file *m, char delimiter, long long num)
 {
 	if (num < 0) {
 		if (m->count + 3 >= m->size) {
 			seq_set_overflow(m);
-			return -1;
+			return;
 		}
 		if (delimiter)
 			m->buf[m->count++] = delimiter;
 		num = -num;
 		delimiter = '-';
 	}
-	return seq_put_decimal_ull(m, delimiter, num);
-
+	seq_put_decimal_ull(m, delimiter, num);
 }
 EXPORT_SYMBOL(seq_put_decimal_ll);
 
diff --git a/include/linux/seq_file.h b/include/linux/seq_file.h
index adeadbd6d7bf..dde00defbaa5 100644
--- a/include/linux/seq_file.h
+++ b/include/linux/seq_file.h
@@ -114,13 +114,18 @@ int seq_open(struct file *, const struct seq_operations *);
 ssize_t seq_read(struct file *, char __user *, size_t, loff_t *);
 loff_t seq_lseek(struct file *, loff_t, int);
 int seq_release(struct inode *, struct file *);
-int seq_escape(struct seq_file *, const char *, const char *);
-int seq_putc(struct seq_file *m, char c);
-int seq_puts(struct seq_file *m, const char *s);
 int seq_write(struct seq_file *seq, const void *data, size_t len);
 
-__printf(2, 3) int seq_printf(struct seq_file *, const char *, ...);
-__printf(2, 0) int seq_vprintf(struct seq_file *, const char *, va_list args);
+__printf(2, 0)
+void seq_vprintf(struct seq_file *m, const char *fmt, va_list args);
+__printf(2, 3)
+void seq_printf(struct seq_file *m, const char *fmt, ...);
+void seq_putc(struct seq_file *m, char c);
+void seq_puts(struct seq_file *m, const char *s);
+void seq_put_decimal_ull(struct seq_file *m, char delimiter,
+			 unsigned long long num);
+void seq_put_decimal_ll(struct seq_file *m, char delimiter, long long num);
+void seq_escape(struct seq_file *m, const char *s, const char *esc);
 
 void seq_hex_dump(struct seq_file *m, const char *prefix_str, int prefix_type,
 		  int rowsize, int groupsize, const void *buf, size_t len,
@@ -138,10 +143,6 @@ int single_release(struct inode *, struct file *);
 void *__seq_open_private(struct file *, const struct seq_operations *, int);
 int seq_open_private(struct file *, const struct seq_operations *, int);
 int seq_release_private(struct inode *, struct file *);
-int seq_put_decimal_ull(struct seq_file *m, char delimiter,
-			unsigned long long num);
-int seq_put_decimal_ll(struct seq_file *m, char delimiter,
-			long long num);
 
 static inline struct user_namespace *seq_user_ns(struct seq_file *seq)
 {
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 08001317aee7..a460e2ef2843 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 e016bd9b1a04..8da542a2874d 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 70ff1d9abf0d..f7b2db44eb4b 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 000000000000..e0b108bd2624
--- /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 02da9f1fd9df..c24b6f767bf0 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 d4988410b410..53abf008ecb3 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 000000000000..536c727a56e9
--- /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 03c3875d9958..a02decf15583 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);
diff --git a/mm/early_ioremap.c b/mm/early_ioremap.c
index 23f744d77ce0..17ae14b5aefa 100644
--- a/mm/early_ioremap.c
+++ b/mm/early_ioremap.c
@@ -15,6 +15,7 @@
 #include <linux/mm.h>
 #include <linux/vmalloc.h>
 #include <asm/fixmap.h>
+#include <asm/early_ioremap.h>
 
 #ifdef CONFIG_MMU
 static int early_ioremap_debug __initdata;
diff --git a/scripts/extract-cert.c b/scripts/extract-cert.c
index fd0db015c65c..10d23ca9f617 100644
--- a/scripts/extract-cert.c
+++ b/scripts/extract-cert.c
@@ -86,7 +86,7 @@ static void write_cert(X509 *x509)
 		ERR(!wb, "%s", cert_dst);
 	}
 	X509_NAME_oneline(X509_get_subject_name(x509), buf, sizeof(buf));
-	ERR(!i2d_X509_bio(wb, x509), cert_dst);
+	ERR(!i2d_X509_bio(wb, x509), "%s", cert_dst);
 	if (kbuild_verbose)
 		fprintf(stderr, "Extracted cert: %s\n", buf);
 }
diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
index 050151144596..89b05e2222c9 100644
--- a/tools/testing/selftests/Makefile
+++ b/tools/testing/selftests/Makefile
@@ -6,6 +6,7 @@ TARGETS += firmware
 TARGETS += ftrace
 TARGETS += futex
 TARGETS += kcmp
+TARGETS += membarrier
 TARGETS += memfd
 TARGETS += memory-hotplug
 TARGETS += mount
diff --git a/tools/testing/selftests/membarrier/.gitignore b/tools/testing/selftests/membarrier/.gitignore
new file mode 100644
index 000000000000..020c44f49a9e
--- /dev/null
+++ b/tools/testing/selftests/membarrier/.gitignore
@@ -0,0 +1 @@
+membarrier_test
diff --git a/tools/testing/selftests/membarrier/Makefile b/tools/testing/selftests/membarrier/Makefile
new file mode 100644
index 000000000000..877a50355d7f
--- /dev/null
+++ b/tools/testing/selftests/membarrier/Makefile
@@ -0,0 +1,11 @@
+CFLAGS += -g -I../../../../usr/include/
+
+all:
+	$(CC) $(CFLAGS) membarrier_test.c -o membarrier_test
+
+TEST_PROGS := membarrier_test
+
+include ../lib.mk
+
+clean:
+	$(RM) membarrier_test
diff --git a/tools/testing/selftests/membarrier/membarrier_test.c b/tools/testing/selftests/membarrier/membarrier_test.c
new file mode 100644
index 000000000000..dde312508007
--- /dev/null
+++ b/tools/testing/selftests/membarrier/membarrier_test.c
@@ -0,0 +1,121 @@
+#define _GNU_SOURCE
+#define __EXPORTED_HEADERS__
+
+#include <linux/membarrier.h>
+#include <asm-generic/unistd.h>
+#include <sys/syscall.h>
+#include <stdio.h>
+#include <errno.h>
+#include <string.h>
+
+#include "../kselftest.h"
+
+enum test_membarrier_status {
+	TEST_MEMBARRIER_PASS = 0,
+	TEST_MEMBARRIER_FAIL,
+	TEST_MEMBARRIER_SKIP,
+};
+
+static int sys_membarrier(int cmd, int flags)
+{
+	return syscall(__NR_membarrier, cmd, flags);
+}
+
+static enum test_membarrier_status test_membarrier_cmd_fail(void)
+{
+	int cmd = -1, flags = 0;
+
+	if (sys_membarrier(cmd, flags) != -1) {
+		printf("membarrier: Wrong command should fail but passed.\n");
+		return TEST_MEMBARRIER_FAIL;
+	}
+	return TEST_MEMBARRIER_PASS;
+}
+
+static enum test_membarrier_status test_membarrier_flags_fail(void)
+{
+	int cmd = MEMBARRIER_CMD_QUERY, flags = 1;
+
+	if (sys_membarrier(cmd, flags) != -1) {
+		printf("membarrier: Wrong flags should fail but passed.\n");
+		return TEST_MEMBARRIER_FAIL;
+	}
+	return TEST_MEMBARRIER_PASS;
+}
+
+static enum test_membarrier_status test_membarrier_success(void)
+{
+	int cmd = MEMBARRIER_CMD_SHARED, flags = 0;
+
+	if (sys_membarrier(cmd, flags) != 0) {
+		printf("membarrier: Executing MEMBARRIER_CMD_SHARED failed. %s.\n",
+				strerror(errno));
+		return TEST_MEMBARRIER_FAIL;
+	}
+
+	printf("membarrier: MEMBARRIER_CMD_SHARED success.\n");
+	return TEST_MEMBARRIER_PASS;
+}
+
+static enum test_membarrier_status test_membarrier(void)
+{
+	enum test_membarrier_status status;
+
+	status = test_membarrier_cmd_fail();
+	if (status)
+		return status;
+	status = test_membarrier_flags_fail();
+	if (status)
+		return status;
+	status = test_membarrier_success();
+	if (status)
+		return status;
+	return TEST_MEMBARRIER_PASS;
+}
+
+static enum test_membarrier_status test_membarrier_query(void)
+{
+	int flags = 0, ret;
+
+	printf("membarrier MEMBARRIER_CMD_QUERY ");
+	ret = sys_membarrier(MEMBARRIER_CMD_QUERY, flags);
+	if (ret < 0) {
+		printf("failed. %s.\n", strerror(errno));
+		switch (errno) {
+		case ENOSYS:
+			/*
+			 * It is valid to build a kernel with
+			 * CONFIG_MEMBARRIER=n. However, this skips the tests.
+			 */
+			return TEST_MEMBARRIER_SKIP;
+		case EINVAL:
+		default:
+			return TEST_MEMBARRIER_FAIL;
+		}
+	}
+	if (!(ret & MEMBARRIER_CMD_SHARED)) {
+		printf("command MEMBARRIER_CMD_SHARED is not supported.\n");
+		return TEST_MEMBARRIER_FAIL;
+	}
+	printf("syscall available.\n");
+	return TEST_MEMBARRIER_PASS;
+}
+
+int main(int argc, char **argv)
+{
+	switch (test_membarrier_query()) {
+	case TEST_MEMBARRIER_FAIL:
+		return ksft_exit_fail();
+	case TEST_MEMBARRIER_SKIP:
+		return ksft_exit_skip();
+	}
+	switch (test_membarrier()) {
+	case TEST_MEMBARRIER_FAIL:
+		return ksft_exit_fail();
+	case TEST_MEMBARRIER_SKIP:
+		return ksft_exit_skip();
+	}
+
+	printf("membarrier: tests done!\n");
+	return ksft_exit_pass();
+}