In isc_log_woudlog() the .logconfig member of isc_log_t structure was
accessed unlocked on the merit that there could be just a race when
.logconfig would be NULL, so the message would not be logged. This
turned not to be true, as there's also data race deeper. The accessed
isc_logconfig_t object could be in the middle of destruction, so the
pointer would be still non-NULL, but the structure members could point
to a chunk of memory no longer belonging to the object. Since we are
only accessing integer types (the log level), this would never lead to
a crash, it leads to memory access to memory area no longer belonging to
the object and this a) wrong, b) raises a red flag in thread-safety tools.
(cherry picked from commit 4d58856ff7)
11a6ac594a