block: make BDRV_POLL_WHILE() re-entrancy safe
Nested BDRV_POLL_WHILE() calls can occur. Currently assert(!wait_->wakeup) fails in AIO_WAIT_WHILE() when this happens. This patch converts the bool wait_->need_kick flag to an unsigned wait_->num_waiters counter. Nesting works correctly because outer AIO_WAIT_WHILE() callers evaluate the condition again after the inner caller completes (invoking the inner caller counts as aio_poll() progress). Reported-by: N"fuweiwei (C)" <fuweiwei2@huawei.com> Reviewed-by: NEric Blake <eblake@redhat.com> Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com> Message-id: 20180307124619.6218-1-stefanha@redhat.com Cc: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>
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