Ticket 49736 - Hardening of active connection list
In case of a bug in the management of the connection refcnt
it can happen that there are several attempts to move a connection
out of the active list.
It triggers a crash because when derefencing c->c_prev.
c_prev is never NULL on the active list
The fix tests if the connection is already out of the active list.
If such case, it just returns.
A potential issue that is not addressed by this fix is:
Thread A and Thread B are using 'c' but c->refcnt=1 (it should be 2)
Thread A "closes" 'c', 'c' is move out of active list (free) because of refcnt=0
A new connection happens selecting the free connection 'c', moving it to the active list.
Thread C is using 'c' from the new connection c->refcnt=1
Thread B "closes" 'c', 'c' is moved out of the active list.
-> new operation coming on 'c' will not be detected
-> Thread C will likely crash when sending result
Reviewed by: Mark Reynolds (thanks!)
Platforms tested: F26
Flag Day: no
Doc impact: no
(cherry picked from commit b0e05806232b781eed3ff102485045a358d7659b)