a59629fcc6
If QEMU forks after the CPU threads have been created, qemu_mutex_lock_iothread will not be able to do qemu_cpu_kick_thread. There is no solution other than assuming that forks after the CPU threads have been created will end up in an exec. Forks before the CPU threads have been created (such as -daemonize) have to call rcu_after_fork manually. Notably, the oxygen theme for GTK+ forks and shows a "No such process" error without this patch. This patch can be reverted once the iothread loses the "kick the TCG thread" magic. User-mode emulation does not use the iothread, so it can also call rcu_after_fork. Reported by: Dr. David Alan Gilbert <dgilbert@redhat.com> Tested by: Dr. David Alan Gilbert <dgilbert@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
157 lines
4.4 KiB
C
157 lines
4.4 KiB
C
#ifndef QEMU_RCU_H
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#define QEMU_RCU_H
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/*
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* urcu-mb.h
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*
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* Userspace RCU header with explicit memory barrier.
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*
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* IBM's contributions to this file may be relicensed under LGPLv2 or later.
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*/
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#include <stdlib.h>
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#include <assert.h>
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#include <limits.h>
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#include <unistd.h>
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#include <stdint.h>
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#include <stdbool.h>
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#include <glib.h>
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#include "qemu/compiler.h"
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#include "qemu/thread.h"
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#include "qemu/queue.h"
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#include "qemu/atomic.h"
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#ifdef __cplusplus
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extern "C" {
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#endif
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/*
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* Important !
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*
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* Each thread containing read-side critical sections must be registered
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* with rcu_register_thread() before calling rcu_read_lock().
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* rcu_unregister_thread() should be called before the thread exits.
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*/
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#ifdef DEBUG_RCU
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#define rcu_assert(args...) assert(args)
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#else
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#define rcu_assert(args...)
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#endif
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/*
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* Global quiescent period counter with low-order bits unused.
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* Using a int rather than a char to eliminate false register dependencies
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* causing stalls on some architectures.
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*/
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extern unsigned long rcu_gp_ctr;
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extern QemuEvent rcu_gp_event;
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struct rcu_reader_data {
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/* Data used by both reader and synchronize_rcu() */
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unsigned long ctr;
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bool waiting;
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/* Data used by reader only */
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unsigned depth;
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/* Data used for registry, protected by rcu_gp_lock */
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QLIST_ENTRY(rcu_reader_data) node;
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};
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extern __thread struct rcu_reader_data rcu_reader;
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static inline void rcu_read_lock(void)
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{
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struct rcu_reader_data *p_rcu_reader = &rcu_reader;
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unsigned ctr;
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if (p_rcu_reader->depth++ > 0) {
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return;
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}
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ctr = atomic_read(&rcu_gp_ctr);
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atomic_xchg(&p_rcu_reader->ctr, ctr);
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if (atomic_read(&p_rcu_reader->waiting)) {
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atomic_set(&p_rcu_reader->waiting, false);
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qemu_event_set(&rcu_gp_event);
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}
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}
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static inline void rcu_read_unlock(void)
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{
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struct rcu_reader_data *p_rcu_reader = &rcu_reader;
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assert(p_rcu_reader->depth != 0);
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if (--p_rcu_reader->depth > 0) {
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return;
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}
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atomic_xchg(&p_rcu_reader->ctr, 0);
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if (atomic_read(&p_rcu_reader->waiting)) {
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atomic_set(&p_rcu_reader->waiting, false);
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qemu_event_set(&rcu_gp_event);
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}
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}
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extern void synchronize_rcu(void);
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/*
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* Reader thread registration.
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*/
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extern void rcu_register_thread(void);
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extern void rcu_unregister_thread(void);
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extern void rcu_after_fork(void);
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struct rcu_head;
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typedef void RCUCBFunc(struct rcu_head *head);
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struct rcu_head {
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struct rcu_head *next;
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RCUCBFunc *func;
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};
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extern void call_rcu1(struct rcu_head *head, RCUCBFunc *func);
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/* The operands of the minus operator must have the same type,
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* which must be the one that we specify in the cast.
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*/
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#define call_rcu(head, func, field) \
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call_rcu1(({ \
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char __attribute__((unused)) \
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offset_must_be_zero[-offsetof(typeof(*(head)), field)], \
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func_type_invalid = (func) - (void (*)(typeof(head)))(func); \
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&(head)->field; \
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}), \
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(RCUCBFunc *)(func))
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#define g_free_rcu(obj, field) \
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call_rcu1(({ \
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char __attribute__((unused)) \
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offset_must_be_zero[-offsetof(typeof(*(obj)), field)]; \
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&(obj)->field; \
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}), \
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(RCUCBFunc *)g_free);
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#ifdef __cplusplus
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}
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#endif
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#endif /* QEMU_RCU_H */
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