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authorLinus Torvalds <torvalds@linux-foundation.org>2017-09-04 08:13:52 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2017-09-04 08:13:52 -0700
commit0081a0ce809b611c1f37da5d6ae5bc8027ffd1c4 (patch)
tree600b4fc3b74d5142fe4a2c2f72d934e6204ca432 /kernel/sched
parentfea1543760351e10e9c573ddf8861c2f23f5b866 (diff)
parent94edf6f3c20c9c8ee301bde04150a91bab4bf32c (diff)
Merge branch 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull RCU updates from Ingo Molnad: "The main RCU related changes in this cycle were: - Removal of spin_unlock_wait() - SRCU updates - RCU torture-test updates - RCU Documentation updates - Extend the sys_membarrier() ABI with the MEMBARRIER_CMD_PRIVATE_EXPEDITED variant - Miscellaneous RCU fixes - CPU-hotplug fixes" * 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (63 commits) arch: Remove spin_unlock_wait() arch-specific definitions locking: Remove spin_unlock_wait() generic definitions drivers/ata: Replace spin_unlock_wait() with lock/unlock pair ipc: Replace spin_unlock_wait() with lock/unlock pair exit: Replace spin_unlock_wait() with lock/unlock pair completion: Replace spin_unlock_wait() with lock/unlock pair doc: Set down RCU's scheduling-clock-interrupt needs doc: No longer allowed to use rcu_dereference on non-pointers doc: Add RCU files to docbook-generation files doc: Update memory-barriers.txt for read-to-write dependencies doc: Update RCU documentation membarrier: Provide expedited private command rcu: Remove exports from rcu_idle_exit() and rcu_idle_enter() rcu: Add warning to rcu_idle_enter() for irqs enabled rcu: Make rcu_idle_enter() rely on callers disabling irqs rcu: Add assertions verifying blocked-tasks list rcu/tracing: Set disable_rcu_irq_enter on rcu_eqs_exit() rcu: Add TPS() protection for _rcu_barrier_trace strings rcu: Use idle versions of swait to make idle-hack clear swait: Add idle variants which don't contribute to load average ...
Diffstat (limited to 'kernel/sched')
-rw-r--r--kernel/sched/Makefile1
-rw-r--r--kernel/sched/completion.c11
-rw-r--r--kernel/sched/core.c38
-rw-r--r--kernel/sched/membarrier.c152
4 files changed, 191 insertions, 11 deletions
diff --git a/kernel/sched/Makefile b/kernel/sched/Makefile
index 53f0164ed362..78f54932ea1d 100644
--- a/kernel/sched/Makefile
+++ b/kernel/sched/Makefile
@@ -25,3 +25,4 @@ obj-$(CONFIG_SCHED_DEBUG) += debug.o
obj-$(CONFIG_CGROUP_CPUACCT) += cpuacct.o
obj-$(CONFIG_CPU_FREQ) += cpufreq.o
obj-$(CONFIG_CPU_FREQ_GOV_SCHEDUTIL) += cpufreq_schedutil.o
+obj-$(CONFIG_MEMBARRIER) += membarrier.o
diff --git a/kernel/sched/completion.c b/kernel/sched/completion.c
index 13fc5ae9bf2f..c9524d2d9316 100644
--- a/kernel/sched/completion.c
+++ b/kernel/sched/completion.c
@@ -300,6 +300,8 @@ EXPORT_SYMBOL(try_wait_for_completion);
*/
bool completion_done(struct completion *x)
{
+ unsigned long flags;
+
if (!READ_ONCE(x->done))
return false;
@@ -307,14 +309,9 @@ bool completion_done(struct completion *x)
* If ->done, we need to wait for complete() to release ->wait.lock
* otherwise we can end up freeing the completion before complete()
* is done referencing it.
- *
- * The RMB pairs with complete()'s RELEASE of ->wait.lock and orders
- * the loads of ->done and ->wait.lock such that we cannot observe
- * the lock before complete() acquires it while observing the ->done
- * after it's acquired the lock.
*/
- smp_rmb();
- spin_unlock_wait(&x->wait.lock);
+ spin_lock_irqsave(&x->wait.lock, flags);
+ spin_unlock_irqrestore(&x->wait.lock, flags);
return true;
}
EXPORT_SYMBOL(completion_done);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0869b20fba81..e053c31d96da 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -951,8 +951,13 @@ struct migration_arg {
static struct rq *__migrate_task(struct rq *rq, struct rq_flags *rf,
struct task_struct *p, int dest_cpu)
{
- if (unlikely(!cpu_active(dest_cpu)))
- return rq;
+ if (p->flags & PF_KTHREAD) {
+ if (unlikely(!cpu_online(dest_cpu)))
+ return rq;
+ } else {
+ if (unlikely(!cpu_active(dest_cpu)))
+ return rq;
+ }
/* Affinity changed (again). */
if (!cpumask_test_cpu(dest_cpu, &p->cpus_allowed))
@@ -2635,6 +2640,16 @@ static struct rq *finish_task_switch(struct task_struct *prev)
prev_state = prev->state;
vtime_task_switch(prev);
perf_event_task_sched_in(prev, current);
+ /*
+ * The membarrier system call requires a full memory barrier
+ * after storing to rq->curr, before going back to user-space.
+ *
+ * TODO: This smp_mb__after_unlock_lock can go away if PPC end
+ * up adding a full barrier to switch_mm(), or we should figure
+ * out if a smp_mb__after_unlock_lock is really the proper API
+ * to use.
+ */
+ smp_mb__after_unlock_lock();
finish_lock_switch(rq, prev);
finish_arch_post_lock_switch();
@@ -3324,6 +3339,21 @@ static void __sched notrace __schedule(bool preempt)
if (likely(prev != next)) {
rq->nr_switches++;
rq->curr = next;
+ /*
+ * The membarrier system call requires each architecture
+ * to have a full memory barrier after updating
+ * rq->curr, before returning to user-space. For TSO
+ * (e.g. x86), the architecture must provide its own
+ * barrier in switch_mm(). For weakly ordered machines
+ * for which spin_unlock() acts as a full memory
+ * barrier, finish_lock_switch() in common code takes
+ * care of this barrier. For weakly ordered machines for
+ * which spin_unlock() acts as a RELEASE barrier (only
+ * arm64 and PowerPC), arm64 has a full barrier in
+ * switch_to(), and PowerPC has
+ * smp_mb__after_unlock_lock() before
+ * finish_lock_switch().
+ */
++*switch_count;
trace_sched_switch(preempt, prev, next);
@@ -3352,8 +3382,8 @@ void __noreturn do_task_dead(void)
* To avoid it, we have to wait for releasing tsk->pi_lock which
* is held by try_to_wake_up()
*/
- smp_mb();
- raw_spin_unlock_wait(&current->pi_lock);
+ raw_spin_lock_irq(&current->pi_lock);
+ raw_spin_unlock_irq(&current->pi_lock);
/* Causes final put_task_struct in finish_task_switch(): */
__set_current_state(TASK_DEAD);
diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c
new file mode 100644
index 000000000000..a92fddc22747
--- /dev/null
+++ b/kernel/sched/membarrier.c
@@ -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;
+ }
+}