When ABE was added (rS331214) to NewReno and leak fixed (rS333699) , it now has
a destructor (newreno_cb_destroy) for per connection state. Other congestion
controls may allocate and free cc_data on entry and exit, but the field is
never explicitly NULLed if moving back to NewReno which only internally
allocates stateful data (no entry contstructor) resulting in a situation where
newreno_cb_destory might be called on a junk pointer.
- NULL out cc_data in the framework after calling {cc}_cb_destroy
- free(9) checks for NULL so there is no need to perform not NULL checks
before calling free.
- Improve a comment about NewReno in tcp_ccalgounload
This is the result of a debugging session from Jason Wolfe, Jason Eggleston,
and mmacy@ and very helpful insight from lstewart@.
Submitted by: Kevin Bowling
Reviewed by: lstewart
Sponsored by: Limelight Networks
Differential Revision: https://reviews.freebsd.org/D16282
2269988749