On 20/12/18 17:37, Stefan Hajnoczi wrote: > On Thu, Dec 20, 2018 at 04:20:28PM +0100, remy.n...@blade-group.com wrote: >> From: Remy Noel <remy.n...@blade-group.com> >> >> It is possible for an io_poll/read/write callback to be concurrently >> executed along >> with an aio_set_fd_handlers. This can cause all sorts of problems, like >> a NULL callback or a bad opaque pointer. >> >> V2: >> * Do not use RCU anymore as it inccurs a performance loss >> V3: >> * Don't drop revents when a handler is modified [Stefan] >> V4: >> * Unregister fd from ctx epoll when removing fd_handler [Paolo] >> >> Remy Noel (2): >> aio-posix: Unregister fd from ctx epoll when removing fd_handler. >> aio-posix: Fix concurrent aio_poll/set_fd_handler. >> >> util/aio-posix.c | 90 +++++++++++++++++++++++++++++------------------- >> util/aio-win32.c | 67 ++++++++++++++++------------------- >> 2 files changed, 84 insertions(+), 73 deletions(-) >> >> -- >> 2.19.2 >> > > Reviewed-by: Stefan Hajnoczi <stefa...@redhat.com> Reviewed-by: Paolo Bonzini <pbonz...@redhat.com>
FWIW, I had missed the early version that used RCU, but lockcnt is already very RCU-like, so not using RCU is the right thing to do. The difference between lockcnt and RCU is that cleanup is done by the reader instead of a separate thread. Because we know that reader/writer concurrency is very rare for AioContext handlers, the tradeoffs favor lockcnt over RCU. Paolo
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