Hi Damjan, Hi Florin, I may have given the wrong example, even though the IP API's marked as mt-safe (VL_API_IP_ROUTE_ADD_DEL/VL_API_IP_ROUTE_ADD_DEL_V2), they'd be called only from the main thread, right? So, only one pool_put will be called and it looks like the patch actually fixes the problem (I still don't like it).
I liked the idea with a vec of freed elements, but we still need to put a worker barrier to perform such an operation. I thought about something more lightweight, like CAS for a newly allocated bitmap/vector. But I find myself extremely incompetent to write any lock-free solutions. On Thu, 4 Nov 2021 at 20:01, Florin Coras <fcoras.li...@gmail.com> wrote: > Agreed! Since pools are not thread safe, the whole load balance destroy > scheme should probably be refactored. > > Maybe add, with locks, the indices to be freed to a vector and once enough > accumulate, or if a new element is needed, grab the worker barrier and > actually free them all. > > Regards, > Florin > > On Nov 4, 2021, at 11:50 AM, Damjan Marion via lists.fd.io < > dmarion=me....@lists.fd.io> wrote: > > > Dear Stanislav, > > It doesn’t look to me as a thread safe solution. > > i.e imagine 2 threads call pool_put_will expand on the same time, and > there is just one free slot. Both will get negative answer, but 2nd put > operation will actually expand. > > — > Damjan > > On 04.11.2021., at 18:24, Stanislav Zaikin <zsta...@gmail.com> wrote: > > > Hello folks, > > In a multi-threaded environment (in my case I have 2 workers) I observed a > crash, and thanks to Neale, it turned out that free_bitmap may expand while > doing pool_put. > Let's say one thread is doing pool_put, while another thread is calling > "pool_elt_at_index". I observed different addresses before and after > checking "ASSERT (! pool_is_free (p, _e))" in that macro. > > I prepared a patch [0], but it's kind of ugly. We don't have asserts in > release mode, so why should we care about it? > > On the other hand, 2 different threads can do 2 pool_puts simultaneously > and we can lose one free element in the pool (and also additionally > allocated bitmap). > > For me, it's a place where it would be nice to have an mt-safe vec. What > do you think? > > [0] - https://gerrit.fd.io/r/c/vpp/+/34332 > > -- > Best regards > Stanislav Zaikin > > > > > > > > -- Best regards Stanislav Zaikin
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