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>

7 files changed, 38 insertions, 37 deletions

diff --git a/system/cpu-throttle.c b/system/cpu-throttle.c
index d9bb30a223..786a9a5639 100644
--- a/system/cpu-throttle.c
+++ b/system/cpu-throttle.c
@@ -57,9 +57,9 @@ static void cpu_throttle_thread(CPUState *cpu, run_on_cpu_data opaque)
             qemu_cond_timedwait_iothread(cpu->halt_cond,
                                          sleeptime_ns / SCALE_MS);
         } else {
-            qemu_mutex_unlock_iothread();
+            bql_unlock();
             g_usleep(sleeptime_ns / SCALE_US);
-            qemu_mutex_lock_iothread();
+            bql_lock();
         }
         sleeptime_ns = endtime_ns - qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
     }
diff --git a/system/cpus.c b/system/cpus.c
index 7d2c28b1d1..1ede629f1f 100644
--- a/system/cpus.c
+++ b/system/cpus.c
@@ -65,7 +65,8 @@
 
 #endif /* CONFIG_LINUX */
 
-static QemuMutex qemu_global_mutex;
+/* The Big QEMU Lock (BQL) */
+static QemuMutex bql;
 
 /*
  * The chosen accelerator is supposed to register this.
@@ -408,14 +409,14 @@ void qemu_init_cpu_loop(void)
     qemu_init_sigbus();
     qemu_cond_init(&qemu_cpu_cond);
     qemu_cond_init(&qemu_pause_cond);
-    qemu_mutex_init(&qemu_global_mutex);
+    qemu_mutex_init(&bql);
 
     qemu_thread_get_self(&io_thread);
 }
 
 void run_on_cpu(CPUState *cpu, run_on_cpu_func func, run_on_cpu_data data)
 {
-    do_run_on_cpu(cpu, func, data, &qemu_global_mutex);
+    do_run_on_cpu(cpu, func, data, &bql);
 }
 
 static void qemu_cpu_stop(CPUState *cpu, bool exit)
@@ -447,7 +448,7 @@ void qemu_wait_io_event(CPUState *cpu)
             slept = true;
             qemu_plugin_vcpu_idle_cb(cpu);
         }
-        qemu_cond_wait(cpu->halt_cond, &qemu_global_mutex);
+        qemu_cond_wait(cpu->halt_cond, &bql);
     }
     if (slept) {
         qemu_plugin_vcpu_resume_cb(cpu);
@@ -500,46 +501,46 @@ bool qemu_in_vcpu_thread(void)
     return current_cpu && qemu_cpu_is_self(current_cpu);
 }
 
-QEMU_DEFINE_STATIC_CO_TLS(bool, iothread_locked)
+QEMU_DEFINE_STATIC_CO_TLS(bool, bql_locked)
 
-bool qemu_mutex_iothread_locked(void)
+bool bql_locked(void)
 {
-    return get_iothread_locked();
+    return get_bql_locked();
 }
 
 bool qemu_in_main_thread(void)
 {
-    return qemu_mutex_iothread_locked();
+    return bql_locked();
 }
 
 /*
  * The BQL is taken from so many places that it is worth profiling the
  * callers directly, instead of funneling them all through a single function.
  */
-void qemu_mutex_lock_iothread_impl(const char *file, int line)
+void bql_lock_impl(const char *file, int line)
 {
-    QemuMutexLockFunc bql_lock = qatomic_read(&qemu_bql_mutex_lock_func);
+    QemuMutexLockFunc bql_lock_fn = qatomic_read(&bql_mutex_lock_func);
 
-    g_assert(!qemu_mutex_iothread_locked());
-    bql_lock(&qemu_global_mutex, file, line);
-    set_iothread_locked(true);
+    g_assert(!bql_locked());
+    bql_lock_fn(&bql, file, line);
+    set_bql_locked(true);
 }
 
-void qemu_mutex_unlock_iothread(void)
+void bql_unlock(void)
 {
-    g_assert(qemu_mutex_iothread_locked());
-    set_iothread_locked(false);
-    qemu_mutex_unlock(&qemu_global_mutex);
+    g_assert(bql_locked());
+    set_bql_locked(false);
+    qemu_mutex_unlock(&bql);
 }
 
 void qemu_cond_wait_iothread(QemuCond *cond)
 {
-    qemu_cond_wait(cond, &qemu_global_mutex);
+    qemu_cond_wait(cond, &bql);
 }
 
 void qemu_cond_timedwait_iothread(QemuCond *cond, int ms)
 {
-    qemu_cond_timedwait(cond, &qemu_global_mutex, ms);
+    qemu_cond_timedwait(cond, &bql, ms);
 }
 
 /* signal CPU creation */
@@ -590,15 +591,15 @@ void pause_all_vcpus(void)
     replay_mutex_unlock();
 
     while (!all_vcpus_paused()) {
-        qemu_cond_wait(&qemu_pause_cond, &qemu_global_mutex);
+        qemu_cond_wait(&qemu_pause_cond, &bql);
         CPU_FOREACH(cpu) {
             qemu_cpu_kick(cpu);
         }
     }
 
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
     replay_mutex_lock();
-    qemu_mutex_lock_iothread();
+    bql_lock();
 }
 
 void cpu_resume(CPUState *cpu)
@@ -627,9 +628,9 @@ void cpu_remove_sync(CPUState *cpu)
     cpu->stop = true;
     cpu->unplug = true;
     qemu_cpu_kick(cpu);
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
     qemu_thread_join(cpu->thread);
-    qemu_mutex_lock_iothread();
+    bql_lock();
 }
 
 void cpus_register_accel(const AccelOpsClass *ops)
@@ -668,7 +669,7 @@ void qemu_init_vcpu(CPUState *cpu)
     cpus_accel->create_vcpu_thread(cpu);
 
     while (!cpu->created) {
-        qemu_cond_wait(&qemu_cpu_cond, &qemu_global_mutex);
+        qemu_cond_wait(&qemu_cpu_cond, &bql);
     }
 }
 
diff --git a/system/dirtylimit.c b/system/dirtylimit.c
index 495c7a7082..b5607eb8c2 100644
--- a/system/dirtylimit.c
+++ b/system/dirtylimit.c
@@ -148,9 +148,9 @@ void vcpu_dirty_rate_stat_stop(void)
 {
     qatomic_set(&vcpu_dirty_rate_stat->running, 0);
     dirtylimit_state_unlock();
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
     qemu_thread_join(&vcpu_dirty_rate_stat->thread);
-    qemu_mutex_lock_iothread();
+    bql_lock();
     dirtylimit_state_lock();
 }
 
diff --git a/system/memory.c b/system/memory.c
index 9ceb229d28..a229a79988 100644
--- a/system/memory.c
+++ b/system/memory.c
@@ -1119,7 +1119,7 @@ void memory_region_transaction_commit(void)
     AddressSpace *as;
 
     assert(memory_region_transaction_depth);
-    assert(qemu_mutex_iothread_locked());
+    assert(bql_locked());
 
     --memory_region_transaction_depth;
     if (!memory_region_transaction_depth) {
diff --git a/system/physmem.c b/system/physmem.c
index a63853a7bc..4937e67bad 100644
--- a/system/physmem.c
+++ b/system/physmem.c
@@ -2639,8 +2639,8 @@ bool prepare_mmio_access(MemoryRegion *mr)
 {
     bool release_lock = false;
 
-    if (!qemu_mutex_iothread_locked()) {
-        qemu_mutex_lock_iothread();
+    if (!bql_locked()) {
+        bql_lock();
         release_lock = true;
     }
     if (mr->flush_coalesced_mmio) {
@@ -2721,7 +2721,7 @@ static MemTxResult flatview_write_continue(FlatView *fv, hwaddr addr,
         }
 
         if (release_lock) {
-            qemu_mutex_unlock_iothread();
+            bql_unlock();
             release_lock = false;
         }
 
@@ -2799,7 +2799,7 @@ MemTxResult flatview_read_continue(FlatView *fv, hwaddr addr,
         }
 
         if (release_lock) {
-            qemu_mutex_unlock_iothread();
+            bql_unlock();
             release_lock = false;
         }
 
diff --git a/system/runstate.c b/system/runstate.c
index 621a023120..fb07b7b71a 100644
--- a/system/runstate.c
+++ b/system/runstate.c
@@ -819,7 +819,7 @@ void qemu_init_subsystems(void)
 
     qemu_init_cpu_list();
     qemu_init_cpu_loop();
-    qemu_mutex_lock_iothread();
+    bql_lock();
 
     atexit(qemu_run_exit_notifiers);
 
diff --git a/system/watchpoint.c b/system/watchpoint.c
index ba5ad13352..b76007ebf6 100644
--- a/system/watchpoint.c
+++ b/system/watchpoint.c
@@ -155,9 +155,9 @@ void cpu_check_watchpoint(CPUState *cpu, vaddr addr, vaddr len,
          * Now raise the debug interrupt so that it will
          * trigger after the current instruction.
          */
-        qemu_mutex_lock_iothread();
+        bql_lock();
         cpu_interrupt(cpu, CPU_INTERRUPT_DEBUG);
-        qemu_mutex_unlock_iothread();
+        bql_unlock();
         return;
     }