system/cpus: rename qemu_mutex_lock_iothread() to bql_lock()

The Big QEMU Lock (BQL) has many names and they are confusing. The
actual QemuMutex variable is called qemu_global_mutex but it's commonly
referred to as the BQL in discussions and some code comments. The
locking APIs, however, are called qemu_mutex_lock_iothread() and
qemu_mutex_unlock_iothread().

The "iothread" name is historic and comes from when the main thread was
split into into KVM vcpu threads and the "iothread" (now called the main
loop thread). I have contributed to the confusion myself by introducing
a separate --object iothread, a separate concept unrelated to the BQL.

The "iothread" name is no longer appropriate for the BQL. Rename the
locking APIs to:
- void bql_lock(void)
- void bql_unlock(void)
- bool bql_locked(void)

There are more APIs with "iothread" in their names. Subsequent patches
will rename them. There are also comments and documentation that will be
updated in later patches.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Paul Durrant <paul@xen.org>
Acked-by: Fabiano Rosas <farosas@suse.de>
Acked-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Acked-by: Peter Xu <peterx@redhat.com>
Acked-by: Eric Farman <farman@linux.ibm.com>
Reviewed-by: Harsh Prateek Bora <harshpb@linux.ibm.com>
Acked-by: Hyman Huang <yong.huang@smartx.com>
Reviewed-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Message-id: 20240102153529.486531-2-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

6 files changed, 78 insertions, 78 deletions

diff --git a/migration/block-dirty-bitmap.c b/migration/block-dirty-bitmap.c
index 24347ab..92e031b 100644
--- a/migration/block-dirty-bitmap.c
+++ b/migration/block-dirty-bitmap.c
@@ -774,7 +774,7 @@ static void dirty_bitmap_state_pending(void *opaque,
     SaveBitmapState *dbms;
     uint64_t pending = 0;
 
-    qemu_mutex_lock_iothread();
+    bql_lock();
 
     QSIMPLEQ_FOREACH(dbms, &s->dbms_list, entry) {
         uint64_t gran = bdrv_dirty_bitmap_granularity(dbms->bitmap);
@@ -784,7 +784,7 @@ static void dirty_bitmap_state_pending(void *opaque,
         pending += DIV_ROUND_UP(sectors * BDRV_SECTOR_SIZE, gran);
     }
 
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
 
     trace_dirty_bitmap_state_pending(pending);
 
diff --git a/migration/block.c b/migration/block.c
index 6ec6a1d..b731d7d 100644
--- a/migration/block.c
+++ b/migration/block.c
@@ -269,7 +269,7 @@ static int mig_save_device_bulk(QEMUFile *f, BlkMigDevState *bmds)
     int64_t count;
 
     if (bmds->shared_base) {
-        qemu_mutex_lock_iothread();
+        bql_lock();
         /* Skip unallocated sectors; intentionally treats failure or
          * partial sector as an allocated sector */
         while (cur_sector < total_sectors &&
@@ -280,7 +280,7 @@ static int mig_save_device_bulk(QEMUFile *f, BlkMigDevState *bmds)
             }
             cur_sector += count >> BDRV_SECTOR_BITS;
         }
-        qemu_mutex_unlock_iothread();
+        bql_unlock();
     }
 
     if (cur_sector >= total_sectors) {
@@ -316,12 +316,12 @@ static int mig_save_device_bulk(QEMUFile *f, BlkMigDevState *bmds)
      * I/O runs in the main loop AioContext (see
      * qemu_get_current_aio_context()).
      */
-    qemu_mutex_lock_iothread();
+    bql_lock();
     bdrv_reset_dirty_bitmap(bmds->dirty_bitmap, cur_sector * BDRV_SECTOR_SIZE,
                             nr_sectors * BDRV_SECTOR_SIZE);
     blk->aiocb = blk_aio_preadv(bb, cur_sector * BDRV_SECTOR_SIZE, &blk->qiov,
                                 0, blk_mig_read_cb, blk);
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
 
     bmds->cur_sector = cur_sector + nr_sectors;
     return (bmds->cur_sector >= total_sectors);
@@ -770,9 +770,9 @@ static int block_save_iterate(QEMUFile *f, void *opaque)
             /* Always called with iothread lock taken for
              * simplicity, block_save_complete also calls it.
              */
-            qemu_mutex_lock_iothread();
+            bql_lock();
             ret = blk_mig_save_dirty_block(f, 1);
-            qemu_mutex_unlock_iothread();
+            bql_unlock();
         }
         if (ret < 0) {
             return ret;
@@ -844,9 +844,9 @@ static void block_state_pending(void *opaque, uint64_t *must_precopy,
     /* Estimate pending number of bytes to send */
     uint64_t pending;
 
-    qemu_mutex_lock_iothread();
+    bql_lock();
     pending = get_remaining_dirty();
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
 
     blk_mig_lock();
     pending += block_mig_state.submitted * BLK_MIG_BLOCK_SIZE +
diff --git a/migration/colo.c b/migration/colo.c
index 4447e34..2a74efd 100644
--- a/migration/colo.c
+++ b/migration/colo.c
@@ -420,13 +420,13 @@ static int colo_do_checkpoint_transaction(MigrationState *s,
     qio_channel_io_seek(QIO_CHANNEL(bioc), 0, 0, NULL);
     bioc->usage = 0;
 
-    qemu_mutex_lock_iothread();
+    bql_lock();
     if (failover_get_state() != FAILOVER_STATUS_NONE) {
-        qemu_mutex_unlock_iothread();
+        bql_unlock();
         goto out;
     }
     vm_stop_force_state(RUN_STATE_COLO);
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
     trace_colo_vm_state_change("run", "stop");
     /*
      * Failover request bh could be called after vm_stop_force_state(),
@@ -435,23 +435,23 @@ static int colo_do_checkpoint_transaction(MigrationState *s,
     if (failover_get_state() != FAILOVER_STATUS_NONE) {
         goto out;
     }
-    qemu_mutex_lock_iothread();
+    bql_lock();
 
     replication_do_checkpoint_all(&local_err);
     if (local_err) {
-        qemu_mutex_unlock_iothread();
+        bql_unlock();
         goto out;
     }
 
     colo_send_message(s->to_dst_file, COLO_MESSAGE_VMSTATE_SEND, &local_err);
     if (local_err) {
-        qemu_mutex_unlock_iothread();
+        bql_unlock();
         goto out;
     }
     /* Note: device state is saved into buffer */
     ret = qemu_save_device_state(fb);
 
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
     if (ret < 0) {
         goto out;
     }
@@ -504,9 +504,9 @@ static int colo_do_checkpoint_transaction(MigrationState *s,
 
     ret = 0;
 
-    qemu_mutex_lock_iothread();
+    bql_lock();
     vm_start();
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
     trace_colo_vm_state_change("stop", "run");
 
 out:
@@ -557,15 +557,15 @@ static void colo_process_checkpoint(MigrationState *s)
     fb = qemu_file_new_output(QIO_CHANNEL(bioc));
     object_unref(OBJECT(bioc));
 
-    qemu_mutex_lock_iothread();
+    bql_lock();
     replication_start_all(REPLICATION_MODE_PRIMARY, &local_err);
     if (local_err) {
-        qemu_mutex_unlock_iothread();
+        bql_unlock();
         goto out;
     }
 
     vm_start();
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
     trace_colo_vm_state_change("stop", "run");
 
     timer_mod(s->colo_delay_timer, qemu_clock_get_ms(QEMU_CLOCK_HOST) +
@@ -639,14 +639,14 @@ out:
 
 void migrate_start_colo_process(MigrationState *s)
 {
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
     qemu_event_init(&s->colo_checkpoint_event, false);
     s->colo_delay_timer =  timer_new_ms(QEMU_CLOCK_HOST,
                                 colo_checkpoint_notify, s);
 
     qemu_sem_init(&s->colo_exit_sem, 0);
     colo_process_checkpoint(s);
-    qemu_mutex_lock_iothread();
+    bql_lock();
 }
 
 static void colo_incoming_process_checkpoint(MigrationIncomingState *mis,
@@ -657,9 +657,9 @@ static void colo_incoming_process_checkpoint(MigrationIncomingState *mis,
     Error *local_err = NULL;
     int ret;
 
-    qemu_mutex_lock_iothread();
+    bql_lock();
     vm_stop_force_state(RUN_STATE_COLO);
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
     trace_colo_vm_state_change("run", "stop");
 
     /* FIXME: This is unnecessary for periodic checkpoint mode */
@@ -677,10 +677,10 @@ static void colo_incoming_process_checkpoint(MigrationIncomingState *mis,
         return;
     }
 
-    qemu_mutex_lock_iothread();
+    bql_lock();
     cpu_synchronize_all_states();
     ret = qemu_loadvm_state_main(mis->from_src_file, mis);
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
 
     if (ret < 0) {
         error_setg(errp, "Load VM's live state (ram) error");
@@ -719,14 +719,14 @@ static void colo_incoming_process_checkpoint(MigrationIncomingState *mis,
         return;
     }
 
-    qemu_mutex_lock_iothread();
+    bql_lock();
     vmstate_loading = true;
     colo_flush_ram_cache();
     ret = qemu_load_device_state(fb);
     if (ret < 0) {
         error_setg(errp, "COLO: load device state failed");
         vmstate_loading = false;
-        qemu_mutex_unlock_iothread();
+        bql_unlock();
         return;
     }
 
@@ -734,7 +734,7 @@ static void colo_incoming_process_checkpoint(MigrationIncomingState *mis,
     if (local_err) {
         error_propagate(errp, local_err);
         vmstate_loading = false;
-        qemu_mutex_unlock_iothread();
+        bql_unlock();
         return;
     }
 
@@ -743,7 +743,7 @@ static void colo_incoming_process_checkpoint(MigrationIncomingState *mis,
     if (local_err) {
         error_propagate(errp, local_err);
         vmstate_loading = false;
-        qemu_mutex_unlock_iothread();
+        bql_unlock();
         return;
     }
     /* Notify all filters of all NIC to do checkpoint */
@@ -752,13 +752,13 @@ static void colo_incoming_process_checkpoint(MigrationIncomingState *mis,
     if (local_err) {
         error_propagate(errp, local_err);
         vmstate_loading = false;
-        qemu_mutex_unlock_iothread();
+        bql_unlock();
         return;
     }
 
     vmstate_loading = false;
     vm_start();
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
     trace_colo_vm_state_change("stop", "run");
 
     if (failover_get_state() == FAILOVER_STATUS_RELAUNCH) {
@@ -851,14 +851,14 @@ static void *colo_process_incoming_thread(void *opaque)
     fb = qemu_file_new_input(QIO_CHANNEL(bioc));
     object_unref(OBJECT(bioc));
 
-    qemu_mutex_lock_iothread();
+    bql_lock();
     replication_start_all(REPLICATION_MODE_SECONDARY, &local_err);
     if (local_err) {
-        qemu_mutex_unlock_iothread();
+        bql_unlock();
         goto out;
     }
     vm_start();
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
     trace_colo_vm_state_change("stop", "run");
 
     colo_send_message(mis->to_src_file, COLO_MESSAGE_CHECKPOINT_READY,
@@ -920,7 +920,7 @@ int coroutine_fn colo_incoming_co(void)
     Error *local_err = NULL;
     QemuThread th;
 
-    assert(qemu_mutex_iothread_locked());
+    assert(bql_locked());
 
     if (!migration_incoming_colo_enabled()) {
         return 0;
@@ -940,10 +940,10 @@ int coroutine_fn colo_incoming_co(void)
     qemu_coroutine_yield();
     mis->colo_incoming_co = NULL;
 
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
     /* Wait checkpoint incoming thread exit before free resource */
     qemu_thread_join(&th);
-    qemu_mutex_lock_iothread();
+    bql_lock();
 
     /* We hold the global iothread lock, so it is safe here */
     colo_release_ram_cache();
diff --git a/migration/dirtyrate.c b/migration/dirtyrate.c
index 62d86b8..1d2e857 100644
--- a/migration/dirtyrate.c
+++ b/migration/dirtyrate.c
@@ -90,13 +90,13 @@ static int64_t do_calculate_dirtyrate(DirtyPageRecord dirty_pages,
 
 void global_dirty_log_change(unsigned int flag, bool start)
 {
-    qemu_mutex_lock_iothread();
+    bql_lock();
     if (start) {
         memory_global_dirty_log_start(flag);
     } else {
         memory_global_dirty_log_stop(flag);
     }
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
 }
 
 /*
@@ -106,12 +106,12 @@ void global_dirty_log_change(unsigned int flag, bool start)
  */
 static void global_dirty_log_sync(unsigned int flag, bool one_shot)
 {
-    qemu_mutex_lock_iothread();
+    bql_lock();
     memory_global_dirty_log_sync(false);
     if (one_shot) {
         memory_global_dirty_log_stop(flag);
     }
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
 }
 
 static DirtyPageRecord *vcpu_dirty_stat_alloc(VcpuStat *stat)
@@ -609,7 +609,7 @@ static void calculate_dirtyrate_dirty_bitmap(struct DirtyRateConfig config)
     int64_t start_time;
     DirtyPageRecord dirty_pages;
 
-    qemu_mutex_lock_iothread();
+    bql_lock();
     memory_global_dirty_log_start(GLOBAL_DIRTY_DIRTY_RATE);
 
     /*
@@ -626,7 +626,7 @@ static void calculate_dirtyrate_dirty_bitmap(struct DirtyRateConfig config)
      * KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE cap is enabled.
      */
     dirtyrate_manual_reset_protect();
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
 
     record_dirtypages_bitmap(&dirty_pages, true);
 
diff --git a/migration/migration.c b/migration/migration.c
index 454cd4e..be173cd 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -1283,12 +1283,12 @@ static void migrate_fd_cleanup(MigrationState *s)
         QEMUFile *tmp;
 
         trace_migrate_fd_cleanup();
-        qemu_mutex_unlock_iothread();
+        bql_unlock();
         if (s->migration_thread_running) {
             qemu_thread_join(&s->thread);
             s->migration_thread_running = false;
         }
-        qemu_mutex_lock_iothread();
+        bql_lock();
 
         multifd_save_cleanup();
         qemu_mutex_lock(&s->qemu_file_lock);
@@ -2396,7 +2396,7 @@ static int postcopy_start(MigrationState *ms, Error **errp)
     }
 
     trace_postcopy_start();
-    qemu_mutex_lock_iothread();
+    bql_lock();
     trace_postcopy_start_set_run();
 
     migration_downtime_start(ms);
@@ -2504,7 +2504,7 @@ static int postcopy_start(MigrationState *ms, Error **errp)
 
     migration_downtime_end(ms);
 
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
 
     if (migrate_postcopy_ram()) {
         /*
@@ -2545,7 +2545,7 @@ fail:
             error_report_err(local_err);
         }
     }
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
     return -1;
 }
 
@@ -2579,14 +2579,14 @@ static int migration_maybe_pause(MigrationState *s,
      * wait for the 'pause_sem' semaphore.
      */
     if (s->state != MIGRATION_STATUS_CANCELLING) {
-        qemu_mutex_unlock_iothread();
+        bql_unlock();
         migrate_set_state(&s->state, *current_active_state,
                           MIGRATION_STATUS_PRE_SWITCHOVER);
         qemu_sem_wait(&s->pause_sem);
         migrate_set_state(&s->state, MIGRATION_STATUS_PRE_SWITCHOVER,
                           new_state);
         *current_active_state = new_state;
-        qemu_mutex_lock_iothread();
+        bql_lock();
     }
 
     return s->state == new_state ? 0 : -EINVAL;
@@ -2597,7 +2597,7 @@ static int migration_completion_precopy(MigrationState *s,
 {
     int ret;
 
-    qemu_mutex_lock_iothread();
+    bql_lock();
     migration_downtime_start(s);
 
     s->vm_old_state = runstate_get();
@@ -2624,7 +2624,7 @@ static int migration_completion_precopy(MigrationState *s,
     ret = qemu_savevm_state_complete_precopy(s->to_dst_file, false,
                                              s->block_inactive);
 out_unlock:
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
     return ret;
 }
 
@@ -2632,9 +2632,9 @@ static void migration_completion_postcopy(MigrationState *s)
 {
     trace_migration_completion_postcopy_end();
 
-    qemu_mutex_lock_iothread();
+    bql_lock();
     qemu_savevm_state_complete_postcopy(s->to_dst_file);
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
 
     /*
      * Shutdown the postcopy fast path thread.  This is only needed when dest
@@ -2658,14 +2658,14 @@ static void migration_completion_failed(MigrationState *s,
          */
         Error *local_err = NULL;
 
-        qemu_mutex_lock_iothread();
+        bql_lock();
         bdrv_activate_all(&local_err);
         if (local_err) {
             error_report_err(local_err);
         } else {
             s->block_inactive = false;
         }
-        qemu_mutex_unlock_iothread();
+        bql_unlock();
     }
 
     migrate_set_state(&s->state, current_active_state,
@@ -3105,7 +3105,7 @@ static void migration_iteration_finish(MigrationState *s)
     /* If we enabled cpu throttling for auto-converge, turn it off. */
     cpu_throttle_stop();
 
-    qemu_mutex_lock_iothread();
+    bql_lock();
     switch (s->state) {
     case MIGRATION_STATUS_COMPLETED:
         migration_calculate_complete(s);
@@ -3136,7 +3136,7 @@ static void migration_iteration_finish(MigrationState *s)
         break;
     }
     migrate_fd_cleanup_schedule(s);
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
 }
 
 static void bg_migration_iteration_finish(MigrationState *s)
@@ -3148,7 +3148,7 @@ static void bg_migration_iteration_finish(MigrationState *s)
      */
     ram_write_tracking_stop();
 
-    qemu_mutex_lock_iothread();
+    bql_lock();
     switch (s->state) {
     case MIGRATION_STATUS_COMPLETED:
         migration_calculate_complete(s);
@@ -3167,7 +3167,7 @@ static void bg_migration_iteration_finish(MigrationState *s)
     }
 
     migrate_fd_cleanup_schedule(s);
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
 }
 
 /*
@@ -3289,9 +3289,9 @@ static void *migration_thread(void *opaque)
     object_ref(OBJECT(s));
     update_iteration_initial_status(s);
 
-    qemu_mutex_lock_iothread();
+    bql_lock();
     qemu_savevm_state_header(s->to_dst_file);
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
 
     /*
      * If we opened the return path, we need to make sure dst has it
@@ -3319,9 +3319,9 @@ static void *migration_thread(void *opaque)
         qemu_savevm_send_colo_enable(s->to_dst_file);
     }
 
-    qemu_mutex_lock_iothread();
+    bql_lock();
     qemu_savevm_state_setup(s->to_dst_file);
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
 
     qemu_savevm_wait_unplug(s, MIGRATION_STATUS_SETUP,
                                MIGRATION_STATUS_ACTIVE);
@@ -3432,10 +3432,10 @@ static void *bg_migration_thread(void *opaque)
     ram_write_tracking_prepare();
 #endif
 
-    qemu_mutex_lock_iothread();
+    bql_lock();
     qemu_savevm_state_header(s->to_dst_file);
     qemu_savevm_state_setup(s->to_dst_file);
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
 
     qemu_savevm_wait_unplug(s, MIGRATION_STATUS_SETUP,
                                MIGRATION_STATUS_ACTIVE);
@@ -3445,7 +3445,7 @@ static void *bg_migration_thread(void *opaque)
     trace_migration_thread_setup_complete();
     migration_downtime_start(s);
 
-    qemu_mutex_lock_iothread();
+    bql_lock();
 
     s->vm_old_state = runstate_get();
 
@@ -3483,7 +3483,7 @@ static void *bg_migration_thread(void *opaque)
     s->vm_start_bh = qemu_bh_new(bg_migration_vm_start_bh, s);
     qemu_bh_schedule(s->vm_start_bh);
 
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
 
     while (migration_is_active(s)) {
         MigIterateState iter_state = bg_migration_iteration_run(s);
@@ -3512,7 +3512,7 @@ fail:
     if (early_fail) {
         migrate_set_state(&s->state, MIGRATION_STATUS_ACTIVE,
                 MIGRATION_STATUS_FAILED);
-        qemu_mutex_unlock_iothread();
+        bql_unlock();
     }
 
     bg_migration_iteration_finish(s);
diff --git a/migration/ram.c b/migration/ram.c
index 8c7886a..08dc7e2 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -2984,9 +2984,9 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
     migration_ops = g_malloc0(sizeof(MigrationOps));
     migration_ops->ram_save_target_page = ram_save_target_page_legacy;
 
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
     ret = multifd_send_sync_main(f);
-    qemu_mutex_lock_iothread();
+    bql_lock();
     if (ret < 0) {
         return ret;
     }
@@ -3221,11 +3221,11 @@ static void ram_state_pending_exact(void *opaque, uint64_t *must_precopy,
     uint64_t remaining_size = rs->migration_dirty_pages * TARGET_PAGE_SIZE;
 
     if (!migration_in_postcopy() && remaining_size < s->threshold_size) {
-        qemu_mutex_lock_iothread();
+        bql_lock();
         WITH_RCU_READ_LOCK_GUARD() {
             migration_bitmap_sync_precopy(rs, false);
         }
-        qemu_mutex_unlock_iothread();
+        bql_unlock();
         remaining_size = rs->migration_dirty_pages * TARGET_PAGE_SIZE;
     }
 
@@ -3453,7 +3453,7 @@ void colo_incoming_start_dirty_log(void)
 {
     RAMBlock *block = NULL;
     /* For memory_global_dirty_log_start below. */
-    qemu_mutex_lock_iothread();
+    bql_lock();
     qemu_mutex_lock_ramlist();
 
     memory_global_dirty_log_sync(false);
@@ -3467,7 +3467,7 @@ void colo_incoming_start_dirty_log(void)
     }
     ram_state->migration_dirty_pages = 0;
     qemu_mutex_unlock_ramlist();
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
 }
 
 /* It is need to hold the global lock to call this helper */