[nickakt]

kernelize_one() takes each sink's lock with a trylock, and kernelize() starts over at once when one is busy. Streams that are each other's sinks hold their own lock while they try the other's, so they start over against each other. After a change of subscriptions all of them are kernelized on their next packet, at the same moment. With about eight or more such streams the restarts do not end: the threads spin with the call's master lock held, the streams' sockets are no longer read, the log fills with "Kernelizing media stream" lines, and commands for the call are not answered. A static lock around kernelize() leaves the trylock only holders outside of it; the call iterators take their list lock ahead of their trylocks in the same way.

A stream with more than RTPE_MAX_FORWARD_DESTINATIONS outputs, two per sink, was pushed to the kernel anyway: the module answered EINVAL, each output ENOENT, and the stream was still marked kernelized. It now takes the no_kernel path.

The limit itself is left as it is. It came with 01a10c0, where it sized the array of outputs in struct rtpengine_list_entry; that struct is gone, and until now the module's check was its only use.