v4.19.13 snapshot.
diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c
new file mode 100644
index 0000000..76e0eaf
--- /dev/null
+++ b/kernel/sched/membarrier.c
@@ -0,0 +1,318 @@
+/*
+ * Copyright (C) 2010-2017 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 "sched.h"
+
+/*
+ * Bitmask made from a "or" of all commands within enum membarrier_cmd,
+ * except MEMBARRIER_CMD_QUERY.
+ */
+#ifdef CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE
+#define MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK \
+ (MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE \
+ | MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE)
+#else
+#define MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK 0
+#endif
+
+#define MEMBARRIER_CMD_BITMASK \
+ (MEMBARRIER_CMD_GLOBAL | MEMBARRIER_CMD_GLOBAL_EXPEDITED \
+ | MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED \
+ | MEMBARRIER_CMD_PRIVATE_EXPEDITED \
+ | MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED \
+ | MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK)
+
+static void ipi_mb(void *info)
+{
+ smp_mb(); /* IPIs should be serializing but paranoid. */
+}
+
+static int membarrier_global_expedited(void)
+{
+ int cpu;
+ bool fallback = false;
+ cpumask_var_t tmpmask;
+
+ if (num_online_cpus() == 1)
+ return 0;
+
+ /*
+ * Matches memory barriers around rq->curr modification in
+ * scheduler.
+ */
+ smp_mb(); /* system call entry is not a mb. */
+
+ /*
+ * Expedited membarrier commands guarantee that they won't
+ * block, hence the GFP_NOWAIT allocation flag and fallback
+ * implementation.
+ */
+ if (!zalloc_cpumask_var(&tmpmask, GFP_NOWAIT)) {
+ /* Fallback for OOM. */
+ fallback = true;
+ }
+
+ cpus_read_lock();
+ for_each_online_cpu(cpu) {
+ struct task_struct *p;
+
+ /*
+ * Skipping the current CPU is OK even through we can be
+ * migrated at any point. The current CPU, at the point
+ * where we read raw_smp_processor_id(), is ensured to
+ * be in program order with respect to the caller
+ * thread. Therefore, we can skip this CPU from the
+ * iteration.
+ */
+ if (cpu == raw_smp_processor_id())
+ continue;
+
+ rcu_read_lock();
+ p = task_rcu_dereference(&cpu_rq(cpu)->curr);
+ if (p && p->mm && (atomic_read(&p->mm->membarrier_state) &
+ MEMBARRIER_STATE_GLOBAL_EXPEDITED)) {
+ if (!fallback)
+ __cpumask_set_cpu(cpu, tmpmask);
+ else
+ smp_call_function_single(cpu, ipi_mb, NULL, 1);
+ }
+ rcu_read_unlock();
+ }
+ if (!fallback) {
+ preempt_disable();
+ smp_call_function_many(tmpmask, ipi_mb, NULL, 1);
+ preempt_enable();
+ free_cpumask_var(tmpmask);
+ }
+ cpus_read_unlock();
+
+ /*
+ * Memory barrier on the caller thread _after_ we finished
+ * waiting for the last IPI. Matches memory barriers around
+ * rq->curr modification in scheduler.
+ */
+ smp_mb(); /* exit from system call is not a mb */
+ return 0;
+}
+
+static int membarrier_private_expedited(int flags)
+{
+ int cpu;
+ bool fallback = false;
+ cpumask_var_t tmpmask;
+
+ if (flags & MEMBARRIER_FLAG_SYNC_CORE) {
+ if (!IS_ENABLED(CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE))
+ return -EINVAL;
+ if (!(atomic_read(¤t->mm->membarrier_state) &
+ MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY))
+ return -EPERM;
+ } else {
+ if (!(atomic_read(¤t->mm->membarrier_state) &
+ MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY))
+ return -EPERM;
+ }
+
+ if (num_online_cpus() == 1)
+ return 0;
+
+ /*
+ * Matches memory barriers around rq->curr modification in
+ * scheduler.
+ */
+ smp_mb(); /* system call entry is not a mb. */
+
+ /*
+ * Expedited membarrier commands guarantee that they won't
+ * block, hence the GFP_NOWAIT allocation flag and fallback
+ * implementation.
+ */
+ if (!zalloc_cpumask_var(&tmpmask, GFP_NOWAIT)) {
+ /* Fallback for OOM. */
+ fallback = true;
+ }
+
+ cpus_read_lock();
+ for_each_online_cpu(cpu) {
+ struct task_struct *p;
+
+ /*
+ * Skipping the current CPU is OK even through we can be
+ * migrated at any point. The current CPU, at the point
+ * where we read raw_smp_processor_id(), is ensured to
+ * be in program order with respect to the caller
+ * thread. Therefore, we can skip this CPU from the
+ * iteration.
+ */
+ if (cpu == raw_smp_processor_id())
+ continue;
+ rcu_read_lock();
+ p = task_rcu_dereference(&cpu_rq(cpu)->curr);
+ if (p && p->mm == current->mm) {
+ if (!fallback)
+ __cpumask_set_cpu(cpu, tmpmask);
+ else
+ smp_call_function_single(cpu, ipi_mb, NULL, 1);
+ }
+ rcu_read_unlock();
+ }
+ if (!fallback) {
+ preempt_disable();
+ smp_call_function_many(tmpmask, ipi_mb, NULL, 1);
+ preempt_enable();
+ free_cpumask_var(tmpmask);
+ }
+ cpus_read_unlock();
+
+ /*
+ * Memory barrier on the caller thread _after_ we finished
+ * waiting for the last IPI. Matches memory barriers around
+ * rq->curr modification in scheduler.
+ */
+ smp_mb(); /* exit from system call is not a mb */
+
+ return 0;
+}
+
+static int membarrier_register_global_expedited(void)
+{
+ struct task_struct *p = current;
+ struct mm_struct *mm = p->mm;
+
+ if (atomic_read(&mm->membarrier_state) &
+ MEMBARRIER_STATE_GLOBAL_EXPEDITED_READY)
+ return 0;
+ atomic_or(MEMBARRIER_STATE_GLOBAL_EXPEDITED, &mm->membarrier_state);
+ if (atomic_read(&mm->mm_users) == 1 && get_nr_threads(p) == 1) {
+ /*
+ * For single mm user, single threaded process, we can
+ * simply issue a memory barrier after setting
+ * MEMBARRIER_STATE_GLOBAL_EXPEDITED to guarantee that
+ * no memory access following registration is reordered
+ * before registration.
+ */
+ smp_mb();
+ } else {
+ /*
+ * For multi-mm user threads, we need to ensure all
+ * future scheduler executions will observe the new
+ * thread flag state for this mm.
+ */
+ synchronize_sched();
+ }
+ atomic_or(MEMBARRIER_STATE_GLOBAL_EXPEDITED_READY,
+ &mm->membarrier_state);
+
+ return 0;
+}
+
+static int membarrier_register_private_expedited(int flags)
+{
+ struct task_struct *p = current;
+ struct mm_struct *mm = p->mm;
+ int state = MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY;
+
+ if (flags & MEMBARRIER_FLAG_SYNC_CORE) {
+ if (!IS_ENABLED(CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE))
+ return -EINVAL;
+ state = MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY;
+ }
+
+ /*
+ * We need to consider threads belonging to different thread
+ * groups, which use the same mm. (CLONE_VM but not
+ * CLONE_THREAD).
+ */
+ if (atomic_read(&mm->membarrier_state) & state)
+ return 0;
+ atomic_or(MEMBARRIER_STATE_PRIVATE_EXPEDITED, &mm->membarrier_state);
+ if (flags & MEMBARRIER_FLAG_SYNC_CORE)
+ atomic_or(MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE,
+ &mm->membarrier_state);
+ if (!(atomic_read(&mm->mm_users) == 1 && get_nr_threads(p) == 1)) {
+ /*
+ * Ensure all future scheduler executions will observe the
+ * new thread flag state for this process.
+ */
+ synchronize_sched();
+ }
+ atomic_or(state, &mm->membarrier_state);
+
+ return 0;
+}
+
+/**
+ * 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, not available on the running
+ * kernel, 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:
+ {
+ int cmd_mask = MEMBARRIER_CMD_BITMASK;
+
+ if (tick_nohz_full_enabled())
+ cmd_mask &= ~MEMBARRIER_CMD_GLOBAL;
+ return cmd_mask;
+ }
+ case MEMBARRIER_CMD_GLOBAL:
+ /* MEMBARRIER_CMD_GLOBAL is not compatible with nohz_full. */
+ if (tick_nohz_full_enabled())
+ return -EINVAL;
+ if (num_online_cpus() > 1)
+ synchronize_sched();
+ return 0;
+ case MEMBARRIER_CMD_GLOBAL_EXPEDITED:
+ return membarrier_global_expedited();
+ case MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED:
+ return membarrier_register_global_expedited();
+ case MEMBARRIER_CMD_PRIVATE_EXPEDITED:
+ return membarrier_private_expedited(0);
+ case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED:
+ return membarrier_register_private_expedited(0);
+ case MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE:
+ return membarrier_private_expedited(MEMBARRIER_FLAG_SYNC_CORE);
+ case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE:
+ return membarrier_register_private_expedited(MEMBARRIER_FLAG_SYNC_CORE);
+ default:
+ return -EINVAL;
+ }
+}