Merge remote-tracking branch 'remotes/stefanha-gitlab/tags/block-pull-request' into staging

Pull request

(Resent due to an email preparation mistake.)

# gpg: Signature made Mon 24 May 2021 14:01:42 BST
# gpg:                using RSA key 8695A8BFD3F97CDAAC35775A9CA4ABB381AB73C8
# gpg: Good signature from "Stefan Hajnoczi <stefanha@redhat.com>" [full]
# gpg:                 aka "Stefan Hajnoczi <stefanha@gmail.com>" [full]
# Primary key fingerprint: 8695 A8BF D3F9 7CDA AC35  775A 9CA4 ABB3 81AB 73C8

* remotes/stefanha-gitlab/tags/block-pull-request:
  coroutine-sleep: introduce qemu_co_sleep
  coroutine-sleep: replace QemuCoSleepState pointer with struct in the API
  coroutine-sleep: move timer out of QemuCoSleepState
  coroutine-sleep: allow qemu_co_sleep_wake that wakes nothing
  coroutine-sleep: disallow NULL QemuCoSleepState** argument
  coroutine-sleep: use a stack-allocated timer
  bitops.h: Improve find_xxx_bit() documentation
  multi-process: Initialize variables declared with g_auto*

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 38 insertions, 37 deletions

diff --git a/util/qemu-coroutine-sleep.c b/util/qemu-coroutine-sleep.c
index 8c4dac4fd7..571ab521ff 100644
--- a/util/qemu-coroutine-sleep.c
+++ b/util/qemu-coroutine-sleep.c
@@ -19,43 +19,34 @@
 
 static const char *qemu_co_sleep_ns__scheduled = "qemu_co_sleep_ns";
 
-struct QemuCoSleepState {
+void qemu_co_sleep_wake(QemuCoSleep *w)
+{
     Coroutine *co;
-    QEMUTimer *ts;
-    QemuCoSleepState **user_state_pointer;
-};
 
-void qemu_co_sleep_wake(QemuCoSleepState *sleep_state)
-{
-    /* Write of schedule protected by barrier write in aio_co_schedule */
-    const char *scheduled = qatomic_cmpxchg(&sleep_state->co->scheduled,
-                                           qemu_co_sleep_ns__scheduled, NULL);
+    co = w->to_wake;
+    w->to_wake = NULL;
+    if (co) {
+        /* Write of schedule protected by barrier write in aio_co_schedule */
+        const char *scheduled = qatomic_cmpxchg(&co->scheduled,
+                                                qemu_co_sleep_ns__scheduled, NULL);
 
-    assert(scheduled == qemu_co_sleep_ns__scheduled);
-    if (sleep_state->user_state_pointer) {
-        *sleep_state->user_state_pointer = NULL;
+        assert(scheduled == qemu_co_sleep_ns__scheduled);
+        aio_co_wake(co);
     }
-    timer_del(sleep_state->ts);
-    aio_co_wake(sleep_state->co);
 }
 
 static void co_sleep_cb(void *opaque)
 {
-    qemu_co_sleep_wake(opaque);
+    QemuCoSleep *w = opaque;
+    qemu_co_sleep_wake(w);
 }
 
-void coroutine_fn qemu_co_sleep_ns_wakeable(QEMUClockType type, int64_t ns,
-                                            QemuCoSleepState **sleep_state)
+void coroutine_fn qemu_co_sleep(QemuCoSleep *w)
 {
-    AioContext *ctx = qemu_get_current_aio_context();
-    QemuCoSleepState state = {
-        .co = qemu_coroutine_self(),
-        .ts = aio_timer_new(ctx, type, SCALE_NS, co_sleep_cb, &state),
-        .user_state_pointer = sleep_state,
-    };
+    Coroutine *co = qemu_coroutine_self();
 
-    const char *scheduled = qatomic_cmpxchg(&state.co->scheduled, NULL,
-                                           qemu_co_sleep_ns__scheduled);
+    const char *scheduled = qatomic_cmpxchg(&co->scheduled, NULL,
+                                            qemu_co_sleep_ns__scheduled);
     if (scheduled) {
         fprintf(stderr,
                 "%s: Co-routine was already scheduled in '%s'\n",
@@ -63,17 +54,27 @@ void coroutine_fn qemu_co_sleep_ns_wakeable(QEMUClockType type, int64_t ns,
         abort();
     }
 
-    if (sleep_state) {
-        *sleep_state = &state;
-    }
-    timer_mod(state.ts, qemu_clock_get_ns(type) + ns);
+    w->to_wake = co;
     qemu_coroutine_yield();
-    if (sleep_state) {
-        /*
-         * Note that *sleep_state is cleared during qemu_co_sleep_wake
-         * before resuming this coroutine.
-         */
-        assert(*sleep_state == NULL);
-    }
-    timer_free(state.ts);
+
+    /* w->to_wake is cleared before resuming this coroutine.  */
+    assert(w->to_wake == NULL);
+}
+
+void coroutine_fn qemu_co_sleep_ns_wakeable(QemuCoSleep *w,
+                                            QEMUClockType type, int64_t ns)
+{
+    AioContext *ctx = qemu_get_current_aio_context();
+    QEMUTimer ts;
+
+    aio_timer_init(ctx, &ts, type, SCALE_NS, co_sleep_cb, w);
+    timer_mod(&ts, qemu_clock_get_ns(type) + ns);
+
+    /*
+     * The timer will fire in the current AiOContext, so the callback
+     * must happen after qemu_co_sleep yields and there is no race
+     * between timer_mod and qemu_co_sleep.
+     */
+    qemu_co_sleep(w);
+    timer_del(&ts);
 }