coroutine-sleep: allow qemu_co_sleep_wake that wakes nothing

All callers of qemu_co_sleep_wake are checking whether they are passing
a NULL argument inside the pointer-to-pointer: do the check in
qemu_co_sleep_wake itself.

As a side effect, qemu_co_sleep_wake can be called more than once and
it will only wake the coroutine once; after the first time, the argument
will be set to NULL via *sleep_state->user_state_pointer.  However, this
would not be safe unless co_sleep_cb keeps using the QemuCoSleepState*
directly, so make it go through the pointer-to-pointer instead.

Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 20210517100548.28806-4-pbonzini@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

3 files changed, 15 insertions, 18 deletions

diff --git a/block/block-copy.c b/block/block-copy.c
index 9b4af00614..f896dc56f2 100644
--- a/block/block-copy.c
+++ b/block/block-copy.c
@@ -674,9 +674,7 @@ out:
 
 void block_copy_kick(BlockCopyCallState *call_state)
 {
-    if (call_state->sleep_state) {
-        qemu_co_sleep_wake(call_state->sleep_state);
-    }
+    qemu_co_sleep_wake(call_state->sleep_state);
 }
 
 /*
diff --git a/block/nbd.c b/block/nbd.c
index 1d4668d42d..1c6315b168 100644
--- a/block/nbd.c
+++ b/block/nbd.c
@@ -289,9 +289,7 @@ static void coroutine_fn nbd_client_co_drain_begin(BlockDriverState *bs)
     BDRVNBDState *s = (BDRVNBDState *)bs->opaque;
 
     s->drained = true;
-    if (s->connection_co_sleep_ns_state) {
-        qemu_co_sleep_wake(s->connection_co_sleep_ns_state);
-    }
+    qemu_co_sleep_wake(s->connection_co_sleep_ns_state);
 
     nbd_co_establish_connection_cancel(bs, false);
 
@@ -330,9 +328,7 @@ static void nbd_teardown_connection(BlockDriverState *bs)
 
     s->state = NBD_CLIENT_QUIT;
     if (s->connection_co) {
-        if (s->connection_co_sleep_ns_state) {
-            qemu_co_sleep_wake(s->connection_co_sleep_ns_state);
-        }
+        qemu_co_sleep_wake(s->connection_co_sleep_ns_state);
         nbd_co_establish_connection_cancel(bs, true);
     }
     if (qemu_in_coroutine()) {
diff --git a/util/qemu-coroutine-sleep.c b/util/qemu-coroutine-sleep.c
index 3f6f637e81..3ae2b5399a 100644
--- a/util/qemu-coroutine-sleep.c
+++ b/util/qemu-coroutine-sleep.c
@@ -27,19 +27,22 @@ struct QemuCoSleepState {
 
 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);
+    if (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);
 
-    assert(scheduled == qemu_co_sleep_ns__scheduled);
-    *sleep_state->user_state_pointer = NULL;
-    timer_del(&sleep_state->ts);
-    aio_co_wake(sleep_state->co);
+        assert(scheduled == qemu_co_sleep_ns__scheduled);
+        *sleep_state->user_state_pointer = NULL;
+        timer_del(&sleep_state->ts);
+        aio_co_wake(sleep_state->co);
+    }
 }
 
 static void co_sleep_cb(void *opaque)
 {
-    qemu_co_sleep_wake(opaque);
+    QemuCoSleepState **sleep_state = opaque;
+    qemu_co_sleep_wake(*sleep_state);
 }
 
 void coroutine_fn qemu_co_sleep_ns_wakeable(QEMUClockType type, int64_t ns,
@@ -60,7 +63,7 @@ void coroutine_fn qemu_co_sleep_ns_wakeable(QEMUClockType type, int64_t ns,
         abort();
     }
 
-    aio_timer_init(ctx, &state.ts, type, SCALE_NS, co_sleep_cb, &state);
+    aio_timer_init(ctx, &state.ts, type, SCALE_NS, co_sleep_cb, sleep_state);
     *sleep_state = &state;
     timer_mod(&state.ts, qemu_clock_get_ns(type) + ns);
     qemu_coroutine_yield();