coroutine: avoid co_queue_wakeup recursion
qemu_aio_coroutine_enter() is (indirectly) called recursively when processing co_queue_wakeup. This can lead to stack exhaustion. This patch rewrites co_queue_wakeup in an iterative fashion (instead of recursive) with bounded memory usage to prevent stack exhaustion. qemu_co_queue_run_restart() is inlined into qemu_aio_coroutine_enter() and the qemu_coroutine_enter() call is turned into a loop to avoid recursion. There is one change that is worth mentioning: Previously, when coroutine A queued coroutine B, qemu_co_queue_run_restart() entered coroutine B from coroutine A. If A was terminating then it would still stay alive until B yielded. After this patch B is entered by A's parent so that a A can be deleted immediately if it is terminating. It is safe to make this change since B could never interact with A if it was terminating anyway. Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com> Reviewed-by: NPaolo Bonzini <pbonzini@redhat.com> Message-id: 20180322152834.12656-3-stefanha@redhat.com Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>
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