|
@@ -0,0 +1,152 @@
|
|
|
+/*
|
|
|
+ * 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 <linux/syscalls.h>
|
|
|
+#include <linux/membarrier.h>
|
|
|
+#include <linux/tick.h>
|
|
|
+#include <linux/cpumask.h>
|
|
|
+
|
|
|
+#include "sched.h" /* for cpu_rq(). */
|
|
|
+
|
|
|
+/*
|
|
|
+ * Bitmask made from a "or" of all commands within enum membarrier_cmd,
|
|
|
+ * except MEMBARRIER_CMD_QUERY.
|
|
|
+ */
|
|
|
+#define MEMBARRIER_CMD_BITMASK \
|
|
|
+ (MEMBARRIER_CMD_SHARED | MEMBARRIER_CMD_PRIVATE_EXPEDITED)
|
|
|
+
|
|
|
+static void ipi_mb(void *info)
|
|
|
+{
|
|
|
+ smp_mb(); /* IPIs should be serializing but paranoid. */
|
|
|
+}
|
|
|
+
|
|
|
+static void membarrier_private_expedited(void)
|
|
|
+{
|
|
|
+ int cpu;
|
|
|
+ bool fallback = false;
|
|
|
+ cpumask_var_t tmpmask;
|
|
|
+
|
|
|
+ if (num_online_cpus() == 1)
|
|
|
+ return;
|
|
|
+
|
|
|
+ /*
|
|
|
+ * 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) {
|
|
|
+ smp_call_function_many(tmpmask, ipi_mb, NULL, 1);
|
|
|
+ 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 */
|
|
|
+}
|
|
|
+
|
|
|
+/**
|
|
|
+ * 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_SHARED;
|
|
|
+ return cmd_mask;
|
|
|
+ }
|
|
|
+ case MEMBARRIER_CMD_SHARED:
|
|
|
+ /* MEMBARRIER_CMD_SHARED 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_PRIVATE_EXPEDITED:
|
|
|
+ membarrier_private_expedited();
|
|
|
+ return 0;
|
|
|
+ default:
|
|
|
+ return -EINVAL;
|
|
|
+ }
|
|
|
+}
|