Em Thu, 3 May 2018 16:52:50 +0200 Hans Verkuil <hverkuil@xxxxxxxxx> escreveu: > From: Hans Verkuil <hans.verkuil@xxxxxxxxx> > Regarding locking: > > There are two request locks used: req_queue_mutex (part of media_device) > ensures high-level serialization of queueing/reiniting and canceling > requests. It serializes STREAMON/OFF, TRY/S_EXT_CTRLS, close() and > MEDIA_REQUEST_IOC_QUEUE. This is the top-level lock and should be taken > before any others. Why it doesn't serialize poll()? > The lock spin_lock in struct media_request protects that structure and > should be held for a short time only. > > Note that VIDIOC_QBUF does not take this mutex: when > a buffer is queued for a request it will add it to the > request by calling media_request_object_bind(), and that returns an > error if the request is in the wrong state. It is serialized via the > spin_lock which in this specific case is sufficient. It looks weird that some syscalls are not serialized. By not having poll() and VIDIOC_QBUF serialized, I'm wandering if playing with them and close() on separate threads won't cause bad locking. Thanks, Mauro
