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coroutine-lock: make qemu_co_enter_next thread-safe

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qemu_co_queue_next does not need to release and re-acquire the mutex,
because the queued coroutine does not run immediately.  However, this
does not hold for qemu_co_enter_next.  Now that qemu_co_queue_wait
can synchronize (via QemuLockable) with code that is not running in
coroutine context, it's important that code using qemu_co_enter_next
can easily use a standardized locking idiom.

First of all, qemu_co_enter_next must use aio_co_wake to restart the
coroutine.  Second, the function gains a second argument, a QemuLockable*,
and the comments of qemu_co_queue_next and qemu_co_queue_restart_all
are adjusted to clarify the difference.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20180203153935.8056-5-pbonzini@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Fam Zheng <famz@redhat.com>
This commit is contained in:
Paolo Bonzini 2018-02-03 10:39:34 -05:00 • committed by Fam Zheng
parent 1a957cf9c4
commit 5261dd7b01
3 changed files with 23 additions and 10 deletions
Download patch file Download diff file Expand all files Collapse all files

10
util/qemu-coroutine-lock.c
View file

@ -132,7 +132,7 @@ void coroutine_fn qemu_co_queue_restart_all(CoQueue *queue)
qemu_co_queue_do_restart(queue, false);
}
bool qemu_co_enter_next(CoQueue *queue)
bool qemu_co_enter_next_impl(CoQueue *queue, QemuLockable *lock)
{
Coroutine *next;
@ -142,7 +142,13 @@ bool qemu_co_enter_next(CoQueue *queue)
}
QSIMPLEQ_REMOVE_HEAD(&queue->entries, co_queue_next);
qemu_coroutine_enter(next);
if (lock) {
qemu_lockable_unlock(lock);
}
aio_co_wake(next);
if (lock) {
qemu_lockable_lock(lock);
}
return true;
}