phosphor: SEGV during phosphor::TraceLog::deregisterThread under ASan

==30022==ERROR: AddressSanitizer: SEGV on unknown address 0x00000c800020 (pc 0x7fe722c90622 bp 0x7fe722e99698 sp 0x7fe71cbfedf0 T2)

    #0 0x7fe722c90621 in std::_Hashtable<phosphor::Sentinel*, phosphor::Sentinel*, std::allocator<phosphor::Sentinel*>, std::__detail::_Identity, std::equal_to<phosphor::Sentinel*>, std::hash<phosphor::Sentinel*>, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<false, true, true> >::_M_find_before_node(unsigned long, phosphor::Sentinel* const&, unsigned long) const /usr/include/c++/5/bits/hashtable.h:1427

    #1 0x7fe722c90621 in std::_Hashtable<phosphor::Sentinel*, phosphor::Sentinel*, std::allocator<phosphor::Sentinel*>, std::__detail::_Identity, std::equal_to<phosphor::Sentinel*>, std::hash<phosphor::Sentinel*>, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<false, true, true> >::_M_erase(std::integral_constant<bool, true>, phosphor::Sentinel* const&) /usr/include/c++/5/bits/hashtable.h:1792

    #2 0x7fe722c90621 in std::_Hashtable<phosphor::Sentinel*, phosphor::Sentinel*, std::allocator<phosphor::Sentinel*>, std::__detail::_Identity, std::equal_to<phosphor::Sentinel*>, std::hash<phosphor::Sentinel*>, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<false, true, true> >::erase(phosphor::Sentinel* const&) /usr/include/c++/5/bits/hashtable.h:749

    #3 0x7fe722c90621 in std::unordered_set<phosphor::Sentinel*, std::hash<phosphor::Sentinel*>, std::equal_to<phosphor::Sentinel*>, std::allocator<phosphor::Sentinel*> >::erase(phosphor::Sentinel* const&) /usr/include/c++/5/bits/unordered_set.h:512

    #4 0x7fe722c90621 in phosphor::TraceLog::deregisterThread() /home/daver/repos/couchbase/server/phosphor/src/trace_log.cc:218

    #5 0x7fe722ea3786 in CouchbaseThread::run() /home/daver/repos/couchbase/server/platform/src/cb_pthreads.cc:60

    #6 0x7fe722ea3786 in platform_thread_wrap /home/daver/repos/couchbase/server/platform/src/cb_pthreads.cc:72

    #7 0x7fe722a646b9 in start_thread (/lib/x86_64-linux-gnu/libpthread.so.0+0x76b9)

    #8 0x7fe7217153dc in clone (/lib/x86_64-linux-gnu/libc.so.6+0x1073dc)

AddressSanitizer can not provide additional info.

SUMMARY: AddressSanitizer: SEGV /usr/include/c++/5/bits/hashtable.h:1427 std::_Hashtable<phosphor::Sentinel*, phosphor::Sentinel*, std::allocator<phosphor::Sentinel*>, std::__detail::_Identity, std::equal_to<phosphor::Sentinel*>, std::hash<phosphor::Sentinel*>, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<false, true, true> >::_M_find_before_node(unsigned long, phosphor::Sentinel* const&, unsigned long) const

Thread T2 (mc:file_logger) created by T0 here:

    #0 0x7fe7247d8253 in pthread_create (/usr/lib/x86_64-linux-gnu/libasan.so.2+0x36253)

    #1 0x7fe722ea3543 in cb_create_named_thread /home/daver/repos/couchbase/server/platform/src/cb_pthreads.cc:110

==30022==ABORTING