[PULL 26/31] migration/postcopy: Replace QemuSemaphore with QemuEvent

[Paolo Bonzini <pbonzini@redhat.com>]

From: Akihiko Odaki <akihiko.odaki@daynix.com>

thread_sync_sem is an one-shot event so it can be converted into
QemuEvent, which is more lightweight.

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20250529-event-v5-9-53b285203794@daynix.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 migration/migration.h    |  4 ++--
 migration/postcopy-ram.c | 10 +++++-----
 migration/savevm.c       |  2 +-
 3 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/migration/migration.h b/migration/migration.h
index aaec471c00f..739289de934 100644
--- a/migration/migration.h
+++ b/migration/migration.h
@@ -98,9 +98,9 @@ struct MigrationIncomingState {
     void (*transport_cleanup)(void *data);
     /*
      * Used to sync thread creations.  Note that we can't create threads in
-     * parallel with this sem.
+     * parallel with this event.
      */
-    QemuSemaphore  thread_sync_sem;
+    QemuEvent  thread_sync_event;
     /*
      * Free at the start of the main state load, set as the main thread finishes
      * loading state.
diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
index 995614b38c9..75fd310fb2b 100644
--- a/migration/postcopy-ram.c
+++ b/migration/postcopy-ram.c
@@ -90,10 +90,10 @@ void postcopy_thread_create(MigrationIncomingState *mis,
                             QemuThread *thread, const char *name,
                             void *(*fn)(void *), int joinable)
 {
-    qemu_sem_init(&mis->thread_sync_sem, 0);
+    qemu_event_init(&mis->thread_sync_event, false);
     qemu_thread_create(thread, name, fn, mis, joinable);
-    qemu_sem_wait(&mis->thread_sync_sem);
-    qemu_sem_destroy(&mis->thread_sync_sem);
+    qemu_event_wait(&mis->thread_sync_event);
+    qemu_event_destroy(&mis->thread_sync_event);
 }
 
 /* Postcopy needs to detect accesses to pages that haven't yet been copied
@@ -964,7 +964,7 @@ static void *postcopy_ram_fault_thread(void *opaque)
     trace_postcopy_ram_fault_thread_entry();
     rcu_register_thread();
     mis->last_rb = NULL; /* last RAMBlock we sent part of */
-    qemu_sem_post(&mis->thread_sync_sem);
+    qemu_event_set(&mis->thread_sync_event);
 
     struct pollfd *pfd;
     size_t pfd_len = 2 + mis->postcopy_remote_fds->len;
@@ -1716,7 +1716,7 @@ void *postcopy_preempt_thread(void *opaque)
 
     rcu_register_thread();
 
-    qemu_sem_post(&mis->thread_sync_sem);
+    qemu_event_set(&mis->thread_sync_event);
 
     /*
      * The preempt channel is established in asynchronous way.  Wait
diff --git a/migration/savevm.c b/migration/savevm.c
index 006514c3e30..52105dd2f10 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -2078,7 +2078,7 @@ static void *postcopy_ram_listen_thread(void *opaque)
 
     migrate_set_state(&mis->state, MIGRATION_STATUS_ACTIVE,
                                    MIGRATION_STATUS_POSTCOPY_ACTIVE);
-    qemu_sem_post(&mis->thread_sync_sem);
+    qemu_event_set(&mis->thread_sync_event);
     trace_postcopy_ram_listen_thread_start();
 
     rcu_register_thread();
-- 
2.49.0