On 17.03.20 17:29, Vitaly Kuznetsov wrote: > David Hildenbrand <david@xxxxxxxxxx> writes: > >> We get the MEM_ONLINE notifier call if memory is added right from the >> kernel via add_memory() or later from user space. >> >> Let's get rid of the "ha_waiting" flag - the wait event has an inbuilt >> mechanism (->done) for that. Initialize the wait event only once and >> reinitialize before adding memory. Unconditionally call complete() and >> wait_for_completion_timeout(). >> >> If there are no waiters, complete() will only increment ->done - which >> will be reset by reinit_completion(). If complete() has already been >> called, wait_for_completion_timeout() will not wait. >> >> There is still the chance for a small race between concurrent >> reinit_completion() and complete(). If complete() wins, we would not >> wait - which is tolerable (and the race exists in current code as >> well). > > How can we see concurent reinit_completion() and complete()? Obvioulsy, > we are not onlining new memory in kernel and hv_mem_hot_add() calls are > serialized, we're waiting up to 5*HZ for the added block to come online > before proceeding to the next one. Or do you mean we actually hit this > 5*HZ timeout, proceeded to the next block and immediately after > reinit_completion() we saw complete() for the previously added block? Yes exactly - or if an admin manually offlines+re-onlines a random memory block. > This is tolerable indeed, we're making forward progress (and this all is > 'best effort' anyway). Exactly my thoughts. [...] > > Reviewed-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> > Thanks! -- Thanks, David / dhildenb
