[Qemu-devel] [PATCH v7 00/73] per-CPU locks

[Emilio G. Cota]

v6: https://lists.gnu.org/archive/html/qemu-devel/2019-01/msg07650.html

All patches in the series have reviews now. Thanks everyone!

I've tested all patches with `make check-qtest -j' for all targets.
The series is checkpatch-clean (just some warnings about __COVERITY__).

You can fetch the series from:
  https://github.com/cota/qemu/tree/cpu-lock-v7

---
v6->v7:

- Rebase on master
  - Add a cpu_halted_set call to arm code that wasn't there in v6

- Add R-b's and Ack's.

- Add comment to patch 3's log to explain why the bitmap is added
  there, even though it only gains a user at the end of the series.

- Fix "prevent deadlock" comments before assertions; use
  "enforce locking order" instead, which is more accurate.

- Add a few more comments, as suggested by Alex.

v6->v7 diff (before rebase) below.

Thanks,

                Emilio
---
diff --git a/accel/tcg/cpu-exec.c b/accel/tcg/cpu-exec.c
index e4ae04f72c..a513457520 100644
--- a/accel/tcg/cpu-exec.c
+++ b/accel/tcg/cpu-exec.c
@@ -435,7 +435,7 @@ static inline bool cpu_handle_halt_locked(CPUState *cpu)
             && replay_interrupt()) {
             X86CPU *x86_cpu = X86_CPU(cpu);
 
-            /* prevent deadlock; cpu_mutex must be acquired _after_ the BQL */
+            /* locking order: cpu_mutex must be acquired _after_ the BQL */
             cpu_mutex_unlock(cpu);
             qemu_mutex_lock_iothread();
             cpu_mutex_lock(cpu);
diff --git a/cpus.c b/cpus.c
index 4f17fe25bf..82a93f2a5a 100644
--- a/cpus.c
+++ b/cpus.c
@@ -2062,7 +2062,7 @@ void qemu_mutex_lock_iothread_impl(const char *file, int 
line)
 {
     QemuMutexLockFunc bql_lock = atomic_read(&qemu_bql_mutex_lock_func);
 
-    /* prevent deadlock with CPU mutex */
+    /* enforce locking order */
     g_assert(no_cpu_mutex_locked());
 
     g_assert(!qemu_mutex_iothread_locked());
diff --git a/include/qom/cpu.h b/include/qom/cpu.h
index bb0729f969..726cb7b090 100644
--- a/include/qom/cpu.h
+++ b/include/qom/cpu.h
@@ -322,7 +322,8 @@ struct qemu_work_item;
  * @mem_io_pc: Host Program Counter at which the memory was accessed.
  * @mem_io_vaddr: Target virtual address at which the memory was accessed.
  * @kvm_fd: vCPU file descriptor for KVM.
- * @lock: Lock to prevent multiple access to per-CPU fields.
+ * @lock: Lock to prevent multiple access to per-CPU fields. Must be acquired
+ *        after the BQL.
  * @cond: Condition variable for per-CPU events.
  * @work_list: List of pending asynchronous work.
  * @halted: Nonzero if the CPU is in suspended state.
@@ -804,6 +805,7 @@ static inline bool cpu_has_work(CPUState *cpu)
     bool (*func)(CPUState *cpu);
     bool ret;
 
+    /* some targets require us to hold the BQL when checking for work */
     if (cc->has_work_with_iothread_lock) {
         if (qemu_mutex_iothread_locked()) {
             func = cc->has_work_with_iothread_lock;
diff --git a/target/i386/kvm.c b/target/i386/kvm.c
index 3f3c670897..65a14deb2f 100644
--- a/target/i386/kvm.c
+++ b/target/i386/kvm.c
@@ -3216,6 +3216,10 @@ void kvm_arch_pre_run(CPUState *cpu, struct kvm_run *run)
         qemu_mutex_lock_iothread();
     }
 
+    /*
+     * We might have cleared some bits in cpu->interrupt_request since reading
+     * it; read it again.
+     */
     interrupt_request = cpu_interrupt_request(cpu);
 
     /* Force the VCPU out of its inner loop to process any INIT requests