* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
- * version 2 of the License, or (at your option) any later version.
+ * version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
*/
#include "qemu/osdep.h"
+#include "qemu/main-loop.h"
#include "exec/cpu-common.h"
-#include "qom/cpu.h"
+#include "hw/core/cpu.h"
#include "sysemu/cpus.h"
+#include "qemu/lockable.h"
static QemuMutex qemu_cpu_list_lock;
static QemuCond exclusive_cond;
static QemuCond exclusive_resume;
static QemuCond qemu_work_cond;
+/* >= 1 if a thread is inside start_exclusive/end_exclusive. Written
+ * under qemu_cpu_list_lock, read with atomic operations.
+ */
static int pending_cpus;
void qemu_init_cpu_list(void)
static int cpu_get_free_index(void)
{
CPUState *some_cpu;
- int cpu_index = 0;
+ int max_cpu_index = 0;
cpu_index_auto_assigned = true;
CPU_FOREACH(some_cpu) {
- cpu_index++;
+ if (some_cpu->cpu_index >= max_cpu_index) {
+ max_cpu_index = some_cpu->cpu_index + 1;
+ }
}
- return cpu_index;
+ return max_cpu_index;
}
-static void finish_safe_work(CPUState *cpu)
-{
- cpu_exec_start(cpu);
- cpu_exec_end(cpu);
-}
+CPUTailQ cpus = QTAILQ_HEAD_INITIALIZER(cpus);
void cpu_list_add(CPUState *cpu)
{
- qemu_mutex_lock(&qemu_cpu_list_lock);
+ QEMU_LOCK_GUARD(&qemu_cpu_list_lock);
if (cpu->cpu_index == UNASSIGNED_CPU_INDEX) {
cpu->cpu_index = cpu_get_free_index();
assert(cpu->cpu_index != UNASSIGNED_CPU_INDEX);
} else {
assert(!cpu_index_auto_assigned);
}
- QTAILQ_INSERT_TAIL(&cpus, cpu, node);
- qemu_mutex_unlock(&qemu_cpu_list_lock);
-
- finish_safe_work(cpu);
+ QTAILQ_INSERT_TAIL_RCU(&cpus, cpu, node);
}
void cpu_list_remove(CPUState *cpu)
{
- qemu_mutex_lock(&qemu_cpu_list_lock);
+ QEMU_LOCK_GUARD(&qemu_cpu_list_lock);
if (!QTAILQ_IN_USE(cpu, node)) {
/* there is nothing to undo since cpu_exec_init() hasn't been called */
- qemu_mutex_unlock(&qemu_cpu_list_lock);
return;
}
- assert(!(cpu_index_auto_assigned && cpu != QTAILQ_LAST(&cpus, CPUTailQ)));
-
- QTAILQ_REMOVE(&cpus, cpu, node);
+ QTAILQ_REMOVE_RCU(&cpus, cpu, node);
cpu->cpu_index = UNASSIGNED_CPU_INDEX;
- qemu_mutex_unlock(&qemu_cpu_list_lock);
}
+CPUState *qemu_get_cpu(int index)
+{
+ CPUState *cpu;
+
+ CPU_FOREACH(cpu) {
+ if (cpu->cpu_index == index) {
+ return cpu;
+ }
+ }
+
+ return NULL;
+}
+
+/* current CPU in the current thread. It is only valid inside cpu_exec() */
+__thread CPUState *current_cpu;
+
struct qemu_work_item {
- struct qemu_work_item *next;
+ QSIMPLEQ_ENTRY(qemu_work_item) node;
run_on_cpu_func func;
- void *data;
- bool free, done;
+ run_on_cpu_data data;
+ bool free, exclusive, done;
};
static void queue_work_on_cpu(CPUState *cpu, struct qemu_work_item *wi)
{
qemu_mutex_lock(&cpu->work_mutex);
- if (cpu->queued_work_first == NULL) {
- cpu->queued_work_first = wi;
- } else {
- cpu->queued_work_last->next = wi;
- }
- cpu->queued_work_last = wi;
- wi->next = NULL;
+ QSIMPLEQ_INSERT_TAIL(&cpu->work_list, wi, node);
wi->done = false;
qemu_mutex_unlock(&cpu->work_mutex);
qemu_cpu_kick(cpu);
}
-void do_run_on_cpu(CPUState *cpu, run_on_cpu_func func, void *data,
+void do_run_on_cpu(CPUState *cpu, run_on_cpu_func func, run_on_cpu_data data,
QemuMutex *mutex)
{
struct qemu_work_item wi;
wi.data = data;
wi.done = false;
wi.free = false;
+ wi.exclusive = false;
queue_work_on_cpu(cpu, &wi);
- while (!atomic_mb_read(&wi.done)) {
+ while (!qatomic_mb_read(&wi.done)) {
CPUState *self_cpu = current_cpu;
qemu_cond_wait(&qemu_work_cond, mutex);
}
}
-void async_run_on_cpu(CPUState *cpu, run_on_cpu_func func, void *data)
+void async_run_on_cpu(CPUState *cpu, run_on_cpu_func func, run_on_cpu_data data)
{
struct qemu_work_item *wi;
}
/* Start an exclusive operation.
- Must only be called from outside cpu_exec, takes
- qemu_cpu_list_lock. */
+ Must only be called from outside cpu_exec. */
void start_exclusive(void)
{
CPUState *other_cpu;
+ int running_cpus;
qemu_mutex_lock(&qemu_cpu_list_lock);
exclusive_idle();
/* Make all other cpus stop executing. */
- pending_cpus = 1;
+ qatomic_set(&pending_cpus, 1);
+
+ /* Write pending_cpus before reading other_cpu->running. */
+ smp_mb();
+ running_cpus = 0;
CPU_FOREACH(other_cpu) {
- if (other_cpu->running) {
- pending_cpus++;
+ if (qatomic_read(&other_cpu->running)) {
+ other_cpu->has_waiter = true;
+ running_cpus++;
qemu_cpu_kick(other_cpu);
}
}
+
+ qatomic_set(&pending_cpus, running_cpus + 1);
while (pending_cpus > 1) {
qemu_cond_wait(&exclusive_cond, &qemu_cpu_list_lock);
}
+
+ /* Can release mutex, no one will enter another exclusive
+ * section until end_exclusive resets pending_cpus to 0.
+ */
+ qemu_mutex_unlock(&qemu_cpu_list_lock);
+
+ current_cpu->in_exclusive_context = true;
}
-/* Finish an exclusive operation. Releases qemu_cpu_list_lock. */
+/* Finish an exclusive operation. */
void end_exclusive(void)
{
- pending_cpus = 0;
+ current_cpu->in_exclusive_context = false;
+
+ qemu_mutex_lock(&qemu_cpu_list_lock);
+ qatomic_set(&pending_cpus, 0);
qemu_cond_broadcast(&exclusive_resume);
qemu_mutex_unlock(&qemu_cpu_list_lock);
}
/* Wait for exclusive ops to finish, and begin cpu execution. */
void cpu_exec_start(CPUState *cpu)
{
- qemu_mutex_lock(&qemu_cpu_list_lock);
- exclusive_idle();
- cpu->running = true;
- qemu_mutex_unlock(&qemu_cpu_list_lock);
+ qatomic_set(&cpu->running, true);
+
+ /* Write cpu->running before reading pending_cpus. */
+ smp_mb();
+
+ /* 1. start_exclusive saw cpu->running == true and pending_cpus >= 1.
+ * After taking the lock we'll see cpu->has_waiter == true and run---not
+ * for long because start_exclusive kicked us. cpu_exec_end will
+ * decrement pending_cpus and signal the waiter.
+ *
+ * 2. start_exclusive saw cpu->running == false but pending_cpus >= 1.
+ * This includes the case when an exclusive item is running now.
+ * Then we'll see cpu->has_waiter == false and wait for the item to
+ * complete.
+ *
+ * 3. pending_cpus == 0. Then start_exclusive is definitely going to
+ * see cpu->running == true, and it will kick the CPU.
+ */
+ if (unlikely(qatomic_read(&pending_cpus))) {
+ QEMU_LOCK_GUARD(&qemu_cpu_list_lock);
+ if (!cpu->has_waiter) {
+ /* Not counted in pending_cpus, let the exclusive item
+ * run. Since we have the lock, just set cpu->running to true
+ * while holding it; no need to check pending_cpus again.
+ */
+ qatomic_set(&cpu->running, false);
+ exclusive_idle();
+ /* Now pending_cpus is zero. */
+ qatomic_set(&cpu->running, true);
+ } else {
+ /* Counted in pending_cpus, go ahead and release the
+ * waiter at cpu_exec_end.
+ */
+ }
+ }
}
/* Mark cpu as not executing, and release pending exclusive ops. */
void cpu_exec_end(CPUState *cpu)
{
- qemu_mutex_lock(&qemu_cpu_list_lock);
- cpu->running = false;
- if (pending_cpus > 1) {
- pending_cpus--;
- if (pending_cpus == 1) {
- qemu_cond_signal(&exclusive_cond);
+ qatomic_set(&cpu->running, false);
+
+ /* Write cpu->running before reading pending_cpus. */
+ smp_mb();
+
+ /* 1. start_exclusive saw cpu->running == true. Then it will increment
+ * pending_cpus and wait for exclusive_cond. After taking the lock
+ * we'll see cpu->has_waiter == true.
+ *
+ * 2. start_exclusive saw cpu->running == false but here pending_cpus >= 1.
+ * This includes the case when an exclusive item started after setting
+ * cpu->running to false and before we read pending_cpus. Then we'll see
+ * cpu->has_waiter == false and not touch pending_cpus. The next call to
+ * cpu_exec_start will run exclusive_idle if still necessary, thus waiting
+ * for the item to complete.
+ *
+ * 3. pending_cpus == 0. Then start_exclusive is definitely going to
+ * see cpu->running == false, and it can ignore this CPU until the
+ * next cpu_exec_start.
+ */
+ if (unlikely(qatomic_read(&pending_cpus))) {
+ QEMU_LOCK_GUARD(&qemu_cpu_list_lock);
+ if (cpu->has_waiter) {
+ cpu->has_waiter = false;
+ qatomic_set(&pending_cpus, pending_cpus - 1);
+ if (pending_cpus == 1) {
+ qemu_cond_signal(&exclusive_cond);
+ }
}
}
- qemu_mutex_unlock(&qemu_cpu_list_lock);
+}
+
+void async_safe_run_on_cpu(CPUState *cpu, run_on_cpu_func func,
+ run_on_cpu_data data)
+{
+ struct qemu_work_item *wi;
+
+ wi = g_malloc0(sizeof(struct qemu_work_item));
+ wi->func = func;
+ wi->data = data;
+ wi->free = true;
+ wi->exclusive = true;
+
+ queue_work_on_cpu(cpu, wi);
}
void process_queued_cpu_work(CPUState *cpu)
{
struct qemu_work_item *wi;
- if (cpu->queued_work_first == NULL) {
+ qemu_mutex_lock(&cpu->work_mutex);
+ if (QSIMPLEQ_EMPTY(&cpu->work_list)) {
+ qemu_mutex_unlock(&cpu->work_mutex);
return;
}
-
- qemu_mutex_lock(&cpu->work_mutex);
- while (cpu->queued_work_first != NULL) {
- wi = cpu->queued_work_first;
- cpu->queued_work_first = wi->next;
- if (!cpu->queued_work_first) {
- cpu->queued_work_last = NULL;
- }
+ while (!QSIMPLEQ_EMPTY(&cpu->work_list)) {
+ wi = QSIMPLEQ_FIRST(&cpu->work_list);
+ QSIMPLEQ_REMOVE_HEAD(&cpu->work_list, node);
qemu_mutex_unlock(&cpu->work_mutex);
- wi->func(cpu, wi->data);
+ if (wi->exclusive) {
+ /* Running work items outside the BQL avoids the following deadlock:
+ * 1) start_exclusive() is called with the BQL taken while another
+ * CPU is running; 2) cpu_exec in the other CPU tries to takes the
+ * BQL, so it goes to sleep; start_exclusive() is sleeping too, so
+ * neither CPU can proceed.
+ */
+ qemu_mutex_unlock_iothread();
+ start_exclusive();
+ wi->func(cpu, wi->data);
+ end_exclusive();
+ qemu_mutex_lock_iothread();
+ } else {
+ wi->func(cpu, wi->data);
+ }
qemu_mutex_lock(&cpu->work_mutex);
if (wi->free) {
g_free(wi);
} else {
- atomic_mb_set(&wi->done, true);
+ qatomic_mb_set(&wi->done, true);
}
}
qemu_mutex_unlock(&cpu->work_mutex);
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