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>

accel/tcg/cpu-exec.c

@@ -558,8 +558,8 @@ static void cpu_exec_longjmp_cleanup(CPUState *cpu)
         tcg_ctx->gen_tb = NULL;
     }
 #endif
-    if (qemu_mutex_iothread_locked()) {
-        qemu_mutex_unlock_iothread();
+    if (bql_locked()) {
+        bql_unlock();
     }
     assert_no_pages_locked();
 }
@@ -680,10 +680,10 @@ static inline bool cpu_handle_halt(CPUState *cpu)
 #if defined(TARGET_I386)
         if (cpu->interrupt_request & CPU_INTERRUPT_POLL) {
             X86CPU *x86_cpu = X86_CPU(cpu);
-            qemu_mutex_lock_iothread();
+            bql_lock();
             apic_poll_irq(x86_cpu->apic_state);
             cpu_reset_interrupt(cpu, CPU_INTERRUPT_POLL);
-            qemu_mutex_unlock_iothread();
+            bql_unlock();
         }
 #endif /* TARGET_I386 */
         if (!cpu_has_work(cpu)) {
@@ -749,9 +749,9 @@ static inline bool cpu_handle_exception(CPUState *cpu, int *ret)
 #else
         if (replay_exception()) {
             CPUClass *cc = CPU_GET_CLASS(cpu);
-            qemu_mutex_lock_iothread();
+            bql_lock();
             cc->tcg_ops->do_interrupt(cpu);
-            qemu_mutex_unlock_iothread();
+            bql_unlock();
             cpu->exception_index = -1;
 
             if (unlikely(cpu->singlestep_enabled)) {
@@ -812,7 +812,7 @@ static inline bool cpu_handle_interrupt(CPUState *cpu,
 
     if (unlikely(qatomic_read(&cpu->interrupt_request))) {
         int interrupt_request;
-        qemu_mutex_lock_iothread();
+        bql_lock();
         interrupt_request = cpu->interrupt_request;
         if (unlikely(cpu->singlestep_enabled & SSTEP_NOIRQ)) {
             /* Mask out external interrupts for this step. */
@@ -821,7 +821,7 @@ static inline bool cpu_handle_interrupt(CPUState *cpu,
         if (interrupt_request & CPU_INTERRUPT_DEBUG) {
             cpu->interrupt_request &= ~CPU_INTERRUPT_DEBUG;
             cpu->exception_index = EXCP_DEBUG;
-            qemu_mutex_unlock_iothread();
+            bql_unlock();
             return true;
         }
 #if !defined(CONFIG_USER_ONLY)
@@ -832,7 +832,7 @@ static inline bool cpu_handle_interrupt(CPUState *cpu,
             cpu->interrupt_request &= ~CPU_INTERRUPT_HALT;
             cpu->halted = 1;
             cpu->exception_index = EXCP_HLT;
-            qemu_mutex_unlock_iothread();
+            bql_unlock();
             return true;
         }
 #if defined(TARGET_I386)
@@ -843,14 +843,14 @@ static inline bool cpu_handle_interrupt(CPUState *cpu,
             cpu_svm_check_intercept_param(env, SVM_EXIT_INIT, 0, 0);
             do_cpu_init(x86_cpu);
             cpu->exception_index = EXCP_HALTED;
-            qemu_mutex_unlock_iothread();
+            bql_unlock();
             return true;
         }
 #else
         else if (interrupt_request & CPU_INTERRUPT_RESET) {
             replay_interrupt();
             cpu_reset(cpu);
-            qemu_mutex_unlock_iothread();
+            bql_unlock();
             return true;
         }
 #endif /* !TARGET_I386 */
@@ -873,7 +873,7 @@ static inline bool cpu_handle_interrupt(CPUState *cpu,
                  */
                 if (unlikely(cpu->singlestep_enabled)) {
                     cpu->exception_index = EXCP_DEBUG;
-                    qemu_mutex_unlock_iothread();
+                    bql_unlock();
                     return true;
                 }
                 cpu->exception_index = -1;
@@ -892,7 +892,7 @@ static inline bool cpu_handle_interrupt(CPUState *cpu,
         }
 
         /* If we exit via cpu_loop_exit/longjmp it is reset in cpu_exec */
-        qemu_mutex_unlock_iothread();
+        bql_unlock();
     }
 
     /* Finally, check if we need to exit to the main loop.  */

accel/tcg/cputlb.c

@@ -2030,10 +2030,10 @@ static uint64_t do_ld_mmio_beN(CPUState *cpu, CPUTLBEntryFull *full,
     section = io_prepare(&mr_offset, cpu, full->xlat_section, attrs, addr, ra);
     mr = section->mr;
 
-    qemu_mutex_lock_iothread();
+    bql_lock();
     ret = int_ld_mmio_beN(cpu, full, ret_be, addr, size, mmu_idx,
                           type, ra, mr, mr_offset);
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
 
     return ret;
 }
@@ -2054,12 +2054,12 @@ static Int128 do_ld16_mmio_beN(CPUState *cpu, CPUTLBEntryFull *full,
     section = io_prepare(&mr_offset, cpu, full->xlat_section, attrs, addr, ra);
     mr = section->mr;
 
-    qemu_mutex_lock_iothread();
+    bql_lock();
     a = int_ld_mmio_beN(cpu, full, ret_be, addr, size - 8, mmu_idx,
                         MMU_DATA_LOAD, ra, mr, mr_offset);
     b = int_ld_mmio_beN(cpu, full, ret_be, addr + size - 8, 8, mmu_idx,
                         MMU_DATA_LOAD, ra, mr, mr_offset + size - 8);
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
 
     return int128_make128(b, a);
 }
@@ -2577,10 +2577,10 @@ static uint64_t do_st_mmio_leN(CPUState *cpu, CPUTLBEntryFull *full,
     section = io_prepare(&mr_offset, cpu, full->xlat_section, attrs, addr, ra);
     mr = section->mr;
 
-    qemu_mutex_lock_iothread();
+    bql_lock();
     ret = int_st_mmio_leN(cpu, full, val_le, addr, size, mmu_idx,
                           ra, mr, mr_offset);
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
 
     return ret;
 }
@@ -2601,12 +2601,12 @@ static uint64_t do_st16_mmio_leN(CPUState *cpu, CPUTLBEntryFull *full,
     section = io_prepare(&mr_offset, cpu, full->xlat_section, attrs, addr, ra);
     mr = section->mr;
 
-    qemu_mutex_lock_iothread();
+    bql_lock();
     int_st_mmio_leN(cpu, full, int128_getlo(val_le), addr, 8,
                     mmu_idx, ra, mr, mr_offset);
     ret = int_st_mmio_leN(cpu, full, int128_gethi(val_le), addr + 8,
                           size - 8, mmu_idx, ra, mr, mr_offset + 8);
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
 
     return ret;
 }

accel/tcg/tcg-accel-ops-icount.c

@@ -126,9 +126,9 @@ void icount_prepare_for_run(CPUState *cpu, int64_t cpu_budget)
          * We're called without the iothread lock, so must take it while
          * we're calling timer handlers.
          */
-        qemu_mutex_lock_iothread();
+        bql_lock();
         icount_notify_aio_contexts();
-        qemu_mutex_unlock_iothread();
+        bql_unlock();
     }
 }
 

accel/tcg/tcg-accel-ops-mttcg.c

@@ -76,7 +76,7 @@ static void *mttcg_cpu_thread_fn(void *arg)
     rcu_add_force_rcu_notifier(&force_rcu.notifier);
     tcg_register_thread();
 
-    qemu_mutex_lock_iothread();
+    bql_lock();
     qemu_thread_get_self(cpu->thread);
 
     cpu->thread_id = qemu_get_thread_id();
@@ -91,9 +91,9 @@ static void *mttcg_cpu_thread_fn(void *arg)
     do {
         if (cpu_can_run(cpu)) {
             int r;
-            qemu_mutex_unlock_iothread();
+            bql_unlock();
             r = tcg_cpus_exec(cpu);
-            qemu_mutex_lock_iothread();
+            bql_lock();
             switch (r) {
             case EXCP_DEBUG:
                 cpu_handle_guest_debug(cpu);
@@ -105,9 +105,9 @@ static void *mttcg_cpu_thread_fn(void *arg)
                  */
                 break;
             case EXCP_ATOMIC:
-                qemu_mutex_unlock_iothread();
+                bql_unlock();
                 cpu_exec_step_atomic(cpu);
-                qemu_mutex_lock_iothread();
+                bql_lock();
             default:
                 /* Ignore everything else? */
                 break;
@@ -119,7 +119,7 @@ static void *mttcg_cpu_thread_fn(void *arg)
     } while (!cpu->unplug || cpu_can_run(cpu));
 
     tcg_cpus_destroy(cpu);
-    qemu_mutex_unlock_iothread();
+    bql_unlock();
     rcu_remove_force_rcu_notifier(&force_rcu.notifier);
     rcu_unregister_thread();
     return NULL;

accel/tcg/tcg-accel-ops-rr.c

@@ -188,7 +188,7 @@ static void *rr_cpu_thread_fn(void *arg)
     rcu_add_force_rcu_notifier(&force_rcu);
     tcg_register_thread();
 
-    qemu_mutex_lock_iothread();
+    bql_lock();
     qemu_thread_get_self(cpu->thread);
 
     cpu->thread_id = qemu_get_thread_id();
@@ -218,9 +218,9 @@ static void *rr_cpu_thread_fn(void *arg)
         /* Only used for icount_enabled() */
         int64_t cpu_budget = 0;
 
-        qemu_mutex_unlock_iothread();
+        bql_unlock();
         replay_mutex_lock();
-        qemu_mutex_lock_iothread();
+        bql_lock();
 
         if (icount_enabled()) {
             int cpu_count = rr_cpu_count();
@@ -254,7 +254,7 @@ static void *rr_cpu_thread_fn(void *arg)
             if (cpu_can_run(cpu)) {
                 int r;
 
-                qemu_mutex_unlock_iothread();
+                bql_unlock();
                 if (icount_enabled()) {
                     icount_prepare_for_run(cpu, cpu_budget);
                 }
@@ -262,15 +262,15 @@ static void *rr_cpu_thread_fn(void *arg)
                 if (icount_enabled()) {
                     icount_process_data(cpu);
                 }
-                qemu_mutex_lock_iothread();
+                bql_lock();
 
                 if (r == EXCP_DEBUG) {
                     cpu_handle_guest_debug(cpu);
                     break;
                 } else if (r == EXCP_ATOMIC) {
-                    qemu_mutex_unlock_iothread();
+                    bql_unlock();
                     cpu_exec_step_atomic(cpu);
-                    qemu_mutex_lock_iothread();
+                    bql_lock();
                     break;
                 }
             } else if (cpu->stop) {

accel/tcg/tcg-accel-ops.c

@@ -88,7 +88,7 @@ static void tcg_cpu_reset_hold(CPUState *cpu)
 /* mask must never be zero, except for A20 change call */
 void tcg_handle_interrupt(CPUState *cpu, int mask)
 {
-    g_assert(qemu_mutex_iothread_locked());
+    g_assert(bql_locked());
 
     cpu->interrupt_request |= mask;
 

accel/tcg/translate-all.c

@@ -649,7 +649,7 @@ void cpu_io_recompile(CPUState *cpu, uintptr_t retaddr)
 
 void cpu_interrupt(CPUState *cpu, int mask)
 {
-    g_assert(qemu_mutex_iothread_locked());
+    g_assert(bql_locked());
     cpu->interrupt_request |= mask;
     qatomic_set(&cpu->neg.icount_decr.u16.high, -1);
 }