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Re: [PATCH v2 7/9] cpus: Introduce qemu_mutex_unlock_iothread_prepare()

From: David Hildenbrand
Subject: Re: [PATCH v2 7/9] cpus: Introduce qemu_mutex_unlock_iothread_prepare()
Date: Tue, 27 Jul 2021 14:59:26 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0

On 23.07.21 21:34, Peter Xu wrote:
The prepare function before unlocking BQL.  There're only three places that can
release the BQL: unlock(), cond_wait() or cond_timedwait().

Signed-off-by: Peter Xu <peterx@redhat.com>
  softmmu/cpus.c | 7 +++++++
  1 file changed, 7 insertions(+)

diff --git a/softmmu/cpus.c b/softmmu/cpus.c
index 9131f77f87..6085f8edbe 100644
--- a/softmmu/cpus.c
+++ b/softmmu/cpus.c
@@ -66,6 +66,10 @@
static QemuMutex qemu_global_mutex; +static void qemu_mutex_unlock_iothread_prepare(void)
  bool cpu_is_stopped(CPUState *cpu)
      return cpu->stopped || !runstate_is_running();
@@ -523,16 +527,19 @@ void qemu_mutex_unlock_iothread(void)
      iothread_locked = false;
+    qemu_mutex_unlock_iothread_prepare();
void qemu_cond_wait_iothread(QemuCond *cond)
+    qemu_mutex_unlock_iothread_prepare();
      qemu_cond_wait(cond, &qemu_global_mutex);
void qemu_cond_timedwait_iothread(QemuCond *cond, int ms)
+    qemu_mutex_unlock_iothread_prepare();
      qemu_cond_timedwait(cond, &qemu_global_mutex, ms);

I'd squash this patch into the next one.

I don't quite like the function name, but don't really have a better suggestion .... maybe qemu_mutex_might_unlock_iothread(), similar to might_sleep() or might_fault() in the kernel. (although here it's pretty clear and not a "might"; could be useful in other context where we might conditionally unlock the BQL at some point in the future, though)


David / dhildenb

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