This is part of a series of changes to remove the implied BQL
from the common code of cpu_handle_interrupt and
cpu_handle_exception.  As part of removing the implied BQL
from the common code, we are pushing the BQL holding
down into the per-arch implementation functions of
do_interrupt and cpu_exec_interrupt.

The purpose of this set of changes is to set the groundwork
so that an arch could move towards removing
the BQL from the cpu_handle_interrupt/exception paths.

This approach was suggested by Paolo Bonzini.
For reference, here are two key posts in the discussion, explaining
the reasoning/benefits of this approach.
https://lists.gnu.org/archive/html/qemu-devel/2020-07/msg08731.html
https://lists.gnu.org/archive/html/qemu-devel/2020-08/msg00044.html

Signed-off-by: Robert Foley <robert.foley@linaro.org>
---
 target/lm32/helper.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/target/lm32/helper.c b/target/lm32/helper.c
index 1130fc8884..4439b06ecc 100644
--- a/target/lm32/helper.c
+++ b/target/lm32/helper.c
@@ -152,6 +152,10 @@ void lm32_cpu_do_interrupt(CPUState *cs)
 {
     LM32CPU *cpu = LM32_CPU(cs);
     CPULM32State *env = &cpu->env;
+    bool bql = !qemu_mutex_iothread_locked();
+    if (bql) {
+        qemu_mutex_lock_iothread();
+    }
 
     qemu_log_mask(CPU_LOG_INT,
             "exception at pc=%x type=%x\n", env->pc, cs->exception_index);
@@ -196,18 +200,24 @@ void lm32_cpu_do_interrupt(CPUState *cs)
                   cs->exception_index);
         break;
     }
+    if (bql) {
+        qemu_mutex_unlock_iothread();
+    }
 }
 
 bool lm32_cpu_exec_interrupt(CPUState *cs, int interrupt_request)
 {
     LM32CPU *cpu = LM32_CPU(cs);
     CPULM32State *env = &cpu->env;
+    qemu_mutex_lock_iothread();
 
     if ((interrupt_request & CPU_INTERRUPT_HARD) && (env->ie & IE_IE)) {
         cs->exception_index = EXCP_IRQ;
         lm32_cpu_do_interrupt(cs);
+        qemu_mutex_unlock_iothread();
         return true;
     }
+    qemu_mutex_unlock_iothread();
     return false;
 }
 
-- 
2.17.1