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https://gitlab.com/qemu-project/qemu
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![Paolo Bonzini](/assets/img/avatar_default.png)
QemuEvent is currently broken on ARM due to missing memory barriers after qatomic_*(). Apart from adding the memory barrier, a closer look reveals some unpaired memory barriers too. Document more clearly what is going on. Reviewed-by: Richard Henderson <richard.henderson@linaro.org> Reviewed-by: David Hildenbrand <david@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
687 lines
17 KiB
C
687 lines
17 KiB
C
/*
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* Wrappers around mutex/cond/thread functions
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*
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* Copyright Red Hat, Inc. 2009
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*
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* Author:
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* Marcelo Tosatti <mtosatti@redhat.com>
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*
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* This work is licensed under the terms of the GNU GPL, version 2 or later.
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* See the COPYING file in the top-level directory.
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*
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*/
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#include "qemu/osdep.h"
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#include "qemu/thread.h"
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#include "qemu/atomic.h"
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#include "qemu/notify.h"
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#include "qemu-thread-common.h"
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#include "qemu/tsan.h"
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#include "qemu/bitmap.h"
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#ifdef CONFIG_PTHREAD_SET_NAME_NP
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#include <pthread_np.h>
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#endif
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static bool name_threads;
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void qemu_thread_naming(bool enable)
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{
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name_threads = enable;
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#if !defined CONFIG_PTHREAD_SETNAME_NP_W_TID && \
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!defined CONFIG_PTHREAD_SETNAME_NP_WO_TID && \
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!defined CONFIG_PTHREAD_SET_NAME_NP
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/* This is a debugging option, not fatal */
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if (enable) {
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fprintf(stderr, "qemu: thread naming not supported on this host\n");
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}
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#endif
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}
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static void error_exit(int err, const char *msg)
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{
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fprintf(stderr, "qemu: %s: %s\n", msg, strerror(err));
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abort();
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}
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static inline clockid_t qemu_timedwait_clockid(void)
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{
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#ifdef CONFIG_PTHREAD_CONDATTR_SETCLOCK
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return CLOCK_MONOTONIC;
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#else
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return CLOCK_REALTIME;
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#endif
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}
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static void compute_abs_deadline(struct timespec *ts, int ms)
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{
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clock_gettime(qemu_timedwait_clockid(), ts);
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ts->tv_nsec += (ms % 1000) * 1000000;
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ts->tv_sec += ms / 1000;
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if (ts->tv_nsec >= 1000000000) {
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ts->tv_sec++;
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ts->tv_nsec -= 1000000000;
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}
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}
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void qemu_mutex_init(QemuMutex *mutex)
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{
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int err;
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err = pthread_mutex_init(&mutex->lock, NULL);
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if (err)
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error_exit(err, __func__);
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qemu_mutex_post_init(mutex);
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}
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void qemu_mutex_destroy(QemuMutex *mutex)
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{
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int err;
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assert(mutex->initialized);
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mutex->initialized = false;
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err = pthread_mutex_destroy(&mutex->lock);
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if (err)
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error_exit(err, __func__);
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}
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void qemu_mutex_lock_impl(QemuMutex *mutex, const char *file, const int line)
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{
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int err;
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assert(mutex->initialized);
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qemu_mutex_pre_lock(mutex, file, line);
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err = pthread_mutex_lock(&mutex->lock);
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if (err)
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error_exit(err, __func__);
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qemu_mutex_post_lock(mutex, file, line);
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}
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int qemu_mutex_trylock_impl(QemuMutex *mutex, const char *file, const int line)
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{
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int err;
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assert(mutex->initialized);
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err = pthread_mutex_trylock(&mutex->lock);
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if (err == 0) {
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qemu_mutex_post_lock(mutex, file, line);
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return 0;
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}
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if (err != EBUSY) {
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error_exit(err, __func__);
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}
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return -EBUSY;
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}
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void qemu_mutex_unlock_impl(QemuMutex *mutex, const char *file, const int line)
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{
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int err;
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assert(mutex->initialized);
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qemu_mutex_pre_unlock(mutex, file, line);
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err = pthread_mutex_unlock(&mutex->lock);
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if (err)
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error_exit(err, __func__);
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}
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void qemu_rec_mutex_init(QemuRecMutex *mutex)
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{
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int err;
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pthread_mutexattr_t attr;
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pthread_mutexattr_init(&attr);
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pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE);
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err = pthread_mutex_init(&mutex->m.lock, &attr);
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pthread_mutexattr_destroy(&attr);
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if (err) {
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error_exit(err, __func__);
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}
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mutex->m.initialized = true;
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}
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void qemu_rec_mutex_destroy(QemuRecMutex *mutex)
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{
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qemu_mutex_destroy(&mutex->m);
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}
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void qemu_rec_mutex_lock_impl(QemuRecMutex *mutex, const char *file, int line)
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{
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qemu_mutex_lock_impl(&mutex->m, file, line);
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}
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int qemu_rec_mutex_trylock_impl(QemuRecMutex *mutex, const char *file, int line)
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{
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return qemu_mutex_trylock_impl(&mutex->m, file, line);
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}
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void qemu_rec_mutex_unlock_impl(QemuRecMutex *mutex, const char *file, int line)
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{
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qemu_mutex_unlock_impl(&mutex->m, file, line);
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}
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void qemu_cond_init(QemuCond *cond)
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{
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pthread_condattr_t attr;
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int err;
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err = pthread_condattr_init(&attr);
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if (err) {
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error_exit(err, __func__);
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}
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#ifdef CONFIG_PTHREAD_CONDATTR_SETCLOCK
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err = pthread_condattr_setclock(&attr, qemu_timedwait_clockid());
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if (err) {
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error_exit(err, __func__);
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}
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#endif
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err = pthread_cond_init(&cond->cond, &attr);
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if (err) {
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error_exit(err, __func__);
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}
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err = pthread_condattr_destroy(&attr);
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if (err) {
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error_exit(err, __func__);
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}
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cond->initialized = true;
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}
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void qemu_cond_destroy(QemuCond *cond)
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{
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int err;
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assert(cond->initialized);
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cond->initialized = false;
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err = pthread_cond_destroy(&cond->cond);
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if (err)
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error_exit(err, __func__);
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}
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void qemu_cond_signal(QemuCond *cond)
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{
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int err;
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assert(cond->initialized);
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err = pthread_cond_signal(&cond->cond);
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if (err)
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error_exit(err, __func__);
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}
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void qemu_cond_broadcast(QemuCond *cond)
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{
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int err;
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assert(cond->initialized);
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err = pthread_cond_broadcast(&cond->cond);
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if (err)
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error_exit(err, __func__);
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}
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void qemu_cond_wait_impl(QemuCond *cond, QemuMutex *mutex, const char *file, const int line)
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{
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int err;
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assert(cond->initialized);
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qemu_mutex_pre_unlock(mutex, file, line);
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err = pthread_cond_wait(&cond->cond, &mutex->lock);
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qemu_mutex_post_lock(mutex, file, line);
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if (err)
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error_exit(err, __func__);
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}
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static bool TSA_NO_TSA
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qemu_cond_timedwait_ts(QemuCond *cond, QemuMutex *mutex, struct timespec *ts,
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const char *file, const int line)
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{
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int err;
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assert(cond->initialized);
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trace_qemu_mutex_unlock(mutex, file, line);
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err = pthread_cond_timedwait(&cond->cond, &mutex->lock, ts);
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trace_qemu_mutex_locked(mutex, file, line);
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if (err && err != ETIMEDOUT) {
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error_exit(err, __func__);
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}
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return err != ETIMEDOUT;
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}
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bool qemu_cond_timedwait_impl(QemuCond *cond, QemuMutex *mutex, int ms,
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const char *file, const int line)
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{
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struct timespec ts;
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compute_abs_deadline(&ts, ms);
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return qemu_cond_timedwait_ts(cond, mutex, &ts, file, line);
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}
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void qemu_sem_init(QemuSemaphore *sem, int init)
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{
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qemu_mutex_init(&sem->mutex);
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qemu_cond_init(&sem->cond);
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if (init < 0) {
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error_exit(EINVAL, __func__);
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}
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sem->count = init;
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}
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void qemu_sem_destroy(QemuSemaphore *sem)
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{
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qemu_cond_destroy(&sem->cond);
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qemu_mutex_destroy(&sem->mutex);
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}
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void qemu_sem_post(QemuSemaphore *sem)
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{
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qemu_mutex_lock(&sem->mutex);
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if (sem->count == UINT_MAX) {
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error_exit(EINVAL, __func__);
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} else {
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sem->count++;
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qemu_cond_signal(&sem->cond);
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}
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qemu_mutex_unlock(&sem->mutex);
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}
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int qemu_sem_timedwait(QemuSemaphore *sem, int ms)
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{
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bool rc = true;
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struct timespec ts;
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compute_abs_deadline(&ts, ms);
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qemu_mutex_lock(&sem->mutex);
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while (sem->count == 0) {
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if (ms == 0) {
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rc = false;
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} else {
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rc = qemu_cond_timedwait_ts(&sem->cond, &sem->mutex, &ts,
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__FILE__, __LINE__);
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}
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if (!rc) { /* timeout */
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break;
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}
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}
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if (rc) {
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--sem->count;
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}
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qemu_mutex_unlock(&sem->mutex);
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return (rc ? 0 : -1);
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}
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void qemu_sem_wait(QemuSemaphore *sem)
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{
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qemu_mutex_lock(&sem->mutex);
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while (sem->count == 0) {
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qemu_cond_wait(&sem->cond, &sem->mutex);
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}
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--sem->count;
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qemu_mutex_unlock(&sem->mutex);
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}
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#ifdef __linux__
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#include "qemu/futex.h"
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#else
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static inline void qemu_futex_wake(QemuEvent *ev, int n)
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{
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assert(ev->initialized);
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pthread_mutex_lock(&ev->lock);
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if (n == 1) {
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pthread_cond_signal(&ev->cond);
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} else {
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pthread_cond_broadcast(&ev->cond);
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}
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pthread_mutex_unlock(&ev->lock);
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}
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static inline void qemu_futex_wait(QemuEvent *ev, unsigned val)
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{
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assert(ev->initialized);
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pthread_mutex_lock(&ev->lock);
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if (ev->value == val) {
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pthread_cond_wait(&ev->cond, &ev->lock);
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}
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pthread_mutex_unlock(&ev->lock);
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}
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#endif
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/* Valid transitions:
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* - free->set, when setting the event
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* - busy->set, when setting the event, followed by qemu_futex_wake
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* - set->free, when resetting the event
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* - free->busy, when waiting
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*
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* set->busy does not happen (it can be observed from the outside but
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* it really is set->free->busy).
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*
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* busy->free provably cannot happen; to enforce it, the set->free transition
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* is done with an OR, which becomes a no-op if the event has concurrently
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* transitioned to free or busy.
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*/
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#define EV_SET 0
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#define EV_FREE 1
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#define EV_BUSY -1
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void qemu_event_init(QemuEvent *ev, bool init)
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{
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#ifndef __linux__
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pthread_mutex_init(&ev->lock, NULL);
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pthread_cond_init(&ev->cond, NULL);
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#endif
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ev->value = (init ? EV_SET : EV_FREE);
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ev->initialized = true;
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}
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void qemu_event_destroy(QemuEvent *ev)
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{
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assert(ev->initialized);
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ev->initialized = false;
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#ifndef __linux__
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pthread_mutex_destroy(&ev->lock);
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pthread_cond_destroy(&ev->cond);
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#endif
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}
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void qemu_event_set(QemuEvent *ev)
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{
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assert(ev->initialized);
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/*
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* Pairs with both qemu_event_reset() and qemu_event_wait().
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*
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* qemu_event_set has release semantics, but because it *loads*
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* ev->value we need a full memory barrier here.
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*/
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smp_mb();
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if (qatomic_read(&ev->value) != EV_SET) {
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int old = qatomic_xchg(&ev->value, EV_SET);
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/* Pairs with memory barrier in kernel futex_wait system call. */
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smp_mb__after_rmw();
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if (old == EV_BUSY) {
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/* There were waiters, wake them up. */
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qemu_futex_wake(ev, INT_MAX);
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}
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}
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}
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void qemu_event_reset(QemuEvent *ev)
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{
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assert(ev->initialized);
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/*
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* If there was a concurrent reset (or even reset+wait),
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* do nothing. Otherwise change EV_SET->EV_FREE.
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*/
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qatomic_or(&ev->value, EV_FREE);
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/*
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* Order reset before checking the condition in the caller.
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* Pairs with the first memory barrier in qemu_event_set().
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*/
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smp_mb__after_rmw();
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}
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void qemu_event_wait(QemuEvent *ev)
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{
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unsigned value;
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assert(ev->initialized);
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/*
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* qemu_event_wait must synchronize with qemu_event_set even if it does
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* not go down the slow path, so this load-acquire is needed that
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* synchronizes with the first memory barrier in qemu_event_set().
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*
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* If we do go down the slow path, there is no requirement at all: we
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* might miss a qemu_event_set() here but ultimately the memory barrier in
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* qemu_futex_wait() will ensure the check is done correctly.
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*/
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value = qatomic_load_acquire(&ev->value);
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if (value != EV_SET) {
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if (value == EV_FREE) {
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/*
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* Leave the event reset and tell qemu_event_set that there are
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* waiters. No need to retry, because there cannot be a concurrent
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* busy->free transition. After the CAS, the event will be either
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* set or busy.
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*
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* This cmpxchg doesn't have particular ordering requirements if it
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* succeeds (moving the store earlier can only cause qemu_event_set()
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* to issue _more_ wakeups), the failing case needs acquire semantics
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* like the load above.
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*/
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if (qatomic_cmpxchg(&ev->value, EV_FREE, EV_BUSY) == EV_SET) {
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return;
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}
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}
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/*
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* This is the final check for a concurrent set, so it does need
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* a smp_mb() pairing with the second barrier of qemu_event_set().
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* The barrier is inside the FUTEX_WAIT system call.
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*/
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qemu_futex_wait(ev, EV_BUSY);
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}
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}
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static __thread NotifierList thread_exit;
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/*
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* Note that in this implementation you can register a thread-exit
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* notifier for the main thread, but it will never be called.
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* This is OK because main thread exit can only happen when the
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* entire process is exiting, and the API allows notifiers to not
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* be called on process exit.
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*/
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void qemu_thread_atexit_add(Notifier *notifier)
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{
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notifier_list_add(&thread_exit, notifier);
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}
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void qemu_thread_atexit_remove(Notifier *notifier)
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{
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notifier_remove(notifier);
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}
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static void qemu_thread_atexit_notify(void *arg)
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{
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/*
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* Called when non-main thread exits (via qemu_thread_exit()
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* or by returning from its start routine.)
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*/
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notifier_list_notify(&thread_exit, NULL);
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}
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typedef struct {
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void *(*start_routine)(void *);
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void *arg;
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char *name;
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} QemuThreadArgs;
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static void *qemu_thread_start(void *args)
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{
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QemuThreadArgs *qemu_thread_args = args;
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void *(*start_routine)(void *) = qemu_thread_args->start_routine;
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void *arg = qemu_thread_args->arg;
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void *r;
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/* Attempt to set the threads name; note that this is for debug, so
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* we're not going to fail if we can't set it.
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*/
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if (name_threads && qemu_thread_args->name) {
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# if defined(CONFIG_PTHREAD_SETNAME_NP_W_TID)
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pthread_setname_np(pthread_self(), qemu_thread_args->name);
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# elif defined(CONFIG_PTHREAD_SETNAME_NP_WO_TID)
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pthread_setname_np(qemu_thread_args->name);
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# elif defined(CONFIG_PTHREAD_SET_NAME_NP)
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pthread_set_name_np(pthread_self(), qemu_thread_args->name);
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# endif
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}
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QEMU_TSAN_ANNOTATE_THREAD_NAME(qemu_thread_args->name);
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g_free(qemu_thread_args->name);
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g_free(qemu_thread_args);
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/*
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* GCC 11 with glibc 2.17 on PowerPC reports
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*
|
||
* qemu-thread-posix.c:540:5: error: ‘__sigsetjmp’ accessing 656 bytes
|
||
* in a region of size 528 [-Werror=stringop-overflow=]
|
||
* 540 | pthread_cleanup_push(qemu_thread_atexit_notify, NULL);
|
||
* | ^~~~~~~~~~~~~~~~~~~~
|
||
*
|
||
* which is clearly nonsense.
|
||
*/
|
||
#pragma GCC diagnostic push
|
||
#ifndef __clang__
|
||
#pragma GCC diagnostic ignored "-Wstringop-overflow"
|
||
#endif
|
||
|
||
pthread_cleanup_push(qemu_thread_atexit_notify, NULL);
|
||
r = start_routine(arg);
|
||
pthread_cleanup_pop(1);
|
||
|
||
#pragma GCC diagnostic pop
|
||
|
||
return r;
|
||
}
|
||
|
||
void qemu_thread_create(QemuThread *thread, const char *name,
|
||
void *(*start_routine)(void*),
|
||
void *arg, int mode)
|
||
{
|
||
sigset_t set, oldset;
|
||
int err;
|
||
pthread_attr_t attr;
|
||
QemuThreadArgs *qemu_thread_args;
|
||
|
||
err = pthread_attr_init(&attr);
|
||
if (err) {
|
||
error_exit(err, __func__);
|
||
}
|
||
|
||
if (mode == QEMU_THREAD_DETACHED) {
|
||
pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
|
||
}
|
||
|
||
/* Leave signal handling to the iothread. */
|
||
sigfillset(&set);
|
||
/* Blocking the signals can result in undefined behaviour. */
|
||
sigdelset(&set, SIGSEGV);
|
||
sigdelset(&set, SIGFPE);
|
||
sigdelset(&set, SIGILL);
|
||
/* TODO avoid SIGBUS loss on macOS */
|
||
pthread_sigmask(SIG_SETMASK, &set, &oldset);
|
||
|
||
qemu_thread_args = g_new0(QemuThreadArgs, 1);
|
||
qemu_thread_args->name = g_strdup(name);
|
||
qemu_thread_args->start_routine = start_routine;
|
||
qemu_thread_args->arg = arg;
|
||
|
||
err = pthread_create(&thread->thread, &attr,
|
||
qemu_thread_start, qemu_thread_args);
|
||
|
||
if (err)
|
||
error_exit(err, __func__);
|
||
|
||
pthread_sigmask(SIG_SETMASK, &oldset, NULL);
|
||
|
||
pthread_attr_destroy(&attr);
|
||
}
|
||
|
||
int qemu_thread_set_affinity(QemuThread *thread, unsigned long *host_cpus,
|
||
unsigned long nbits)
|
||
{
|
||
#if defined(CONFIG_PTHREAD_AFFINITY_NP)
|
||
const size_t setsize = CPU_ALLOC_SIZE(nbits);
|
||
unsigned long value;
|
||
cpu_set_t *cpuset;
|
||
int err;
|
||
|
||
cpuset = CPU_ALLOC(nbits);
|
||
g_assert(cpuset);
|
||
|
||
CPU_ZERO_S(setsize, cpuset);
|
||
value = find_first_bit(host_cpus, nbits);
|
||
while (value < nbits) {
|
||
CPU_SET_S(value, setsize, cpuset);
|
||
value = find_next_bit(host_cpus, nbits, value + 1);
|
||
}
|
||
|
||
err = pthread_setaffinity_np(thread->thread, setsize, cpuset);
|
||
CPU_FREE(cpuset);
|
||
return err;
|
||
#else
|
||
return -ENOSYS;
|
||
#endif
|
||
}
|
||
|
||
int qemu_thread_get_affinity(QemuThread *thread, unsigned long **host_cpus,
|
||
unsigned long *nbits)
|
||
{
|
||
#if defined(CONFIG_PTHREAD_AFFINITY_NP)
|
||
unsigned long tmpbits;
|
||
cpu_set_t *cpuset;
|
||
size_t setsize;
|
||
int i, err;
|
||
|
||
tmpbits = CPU_SETSIZE;
|
||
while (true) {
|
||
setsize = CPU_ALLOC_SIZE(tmpbits);
|
||
cpuset = CPU_ALLOC(tmpbits);
|
||
g_assert(cpuset);
|
||
|
||
err = pthread_getaffinity_np(thread->thread, setsize, cpuset);
|
||
if (err) {
|
||
CPU_FREE(cpuset);
|
||
if (err != -EINVAL) {
|
||
return err;
|
||
}
|
||
tmpbits *= 2;
|
||
} else {
|
||
break;
|
||
}
|
||
}
|
||
|
||
/* Convert the result into a proper bitmap. */
|
||
*nbits = tmpbits;
|
||
*host_cpus = bitmap_new(tmpbits);
|
||
for (i = 0; i < tmpbits; i++) {
|
||
if (CPU_ISSET(i, cpuset)) {
|
||
set_bit(i, *host_cpus);
|
||
}
|
||
}
|
||
CPU_FREE(cpuset);
|
||
return 0;
|
||
#else
|
||
return -ENOSYS;
|
||
#endif
|
||
}
|
||
|
||
void qemu_thread_get_self(QemuThread *thread)
|
||
{
|
||
thread->thread = pthread_self();
|
||
}
|
||
|
||
bool qemu_thread_is_self(QemuThread *thread)
|
||
{
|
||
return pthread_equal(pthread_self(), thread->thread);
|
||
}
|
||
|
||
void qemu_thread_exit(void *retval)
|
||
{
|
||
pthread_exit(retval);
|
||
}
|
||
|
||
void *qemu_thread_join(QemuThread *thread)
|
||
{
|
||
int err;
|
||
void *ret;
|
||
|
||
err = pthread_join(thread->thread, &ret);
|
||
if (err) {
|
||
error_exit(err, __func__);
|
||
}
|
||
return ret;
|
||
}
|