osd: fix racy accesses to OSD::osdmap.

Accordingly to cppreference.com [1]:

  "If multiple threads of execution access the same std::shared_ptr
  object without synchronization and any of those accesses uses
  a non-const member function of shared_ptr then a data race will
  occur (...)"

[1]: https://en.cppreference.com/w/cpp/memory/shared_ptr/atomic

One of the coredumps showed the `shared_ptr`-typed `OSD::osdmap`
with healthy looking content but damaged control block:

  ```
  [Current thread is 1 (Thread 0x7f7dcaf73700 (LWP 205295))]
  (gdb) bt
  #0  0x0000559cb81c3ea0 in ?? ()
  #1  0x0000559c97675b27 in std::_Sp_counted_base<(__gnu_cxx::_Lock_policy)2>::_M_release (this=0x559cba0ec900) at /usr/include/c++/8/bits/shared_ptr_base.h:148
  #2  std::_Sp_counted_base<(__gnu_cxx::_Lock_policy)2>::_M_release (this=0x559cba0ec900) at /usr/include/c++/8/bits/shared_ptr_base.h:148
  #3  0x0000559c975ef8aa in std::__shared_count<(__gnu_cxx::_Lock_policy)2>::~__shared_count (this=<optimized out>, __in_chrg=<optimized out>) at /usr/include/c++/8/bits/shared_ptr_base.h:1167
  #4  std::__shared_ptr<OSDMap const, (__gnu_cxx::_Lock_policy)2>::~__shared_ptr (this=<optimized out>, __in_chrg=<optimized out>) at /usr/include/c++/8/bits/shared_ptr_base.h:1167
  #5  std::shared_ptr<OSDMap const>::~shared_ptr (this=<optimized out>, __in_chrg=<optimized out>) at /usr/include/c++/8/bits/shared_ptr.h:103
  #6  OSD::create_context (this=<optimized out>) at /usr/src/debug/ceph-15.0.0-10071.g5b5a3a3.el8.x86_64/src/osd/OSD.cc:9053
  #7  0x0000559c97655571 in OSD::dequeue_peering_evt (this=0x559ca22ac000, sdata=0x559ca2ef2900, pg=0x559cb4aa3400, evt=std::shared_ptr<PGPeeringEvent> (use count 2, weak count 0) = {...}, handle=...)
      at /usr/src/debug/ceph-15.0.0-10071.g5b5a3a3.el8.x86_64/src/osd/OSD.cc:9665
  #8  0x0000559c97886db6 in ceph::osd::scheduler::PGPeeringItem::run (this=<optimized out>, osd=<optimized out>, sdata=<optimized out>, pg=..., handle=...) at /usr/include/c++/8/ext/atomicity.h:96
  #9  0x0000559c9764862f in ceph::osd::scheduler::OpSchedulerItem::run (handle=..., pg=..., sdata=<optimized out>, osd=<optimized out>, this=0x7f7dcaf703f0) at /usr/include/c++/8/bits/unique_ptr.h:342
  #10 OSD::ShardedOpWQ::_process (this=<optimized out>, thread_index=<optimized out>, hb=<optimized out>) at /usr/src/debug/ceph-15.0.0-10071.g5b5a3a3.el8.x86_64/src/osd/OSD.cc:10677
  #11 0x0000559c97c76094 in ShardedThreadPool::shardedthreadpool_worker (this=0x559ca22aca28, thread_index=14) at /usr/src/debug/ceph-15.0.0-10071.g5b5a3a3.el8.x86_64/src/common/WorkQueue.cc:311
  #12 0x0000559c97c78cf4 in ShardedThreadPool::WorkThreadSharded::entry (this=<optimized out>) at /usr/src/debug/ceph-15.0.0-10071.g5b5a3a3.el8.x86_64/src/common/WorkQueue.h:706
  #13 0x00007f7df17852de in start_thread () from /lib64/libpthread.so.0
  #14 0x00007f7df052f133 in __libc_ifunc_impl_list () from /lib64/libc.so.6
  #15 0x0000000000000000 in ?? ()
  (gdb) frame 7
  #7  0x0000559c97655571 in OSD::dequeue_peering_evt (this=0x559ca22ac000, sdata=0x559ca2ef2900, pg=0x559cb4aa3400, evt=std::shared_ptr<PGPeeringEvent> (use count 2, weak count 0) = {...}, handle=...)
      at /usr/src/debug/ceph-15.0.0-10071.g5b5a3a3.el8.x86_64/src/osd/OSD.cc:9665
  9665      in /usr/src/debug/ceph-15.0.0-10071.g5b5a3a3.el8.x86_64/src/osd/OSD.cc
  (gdb) print osdmap
  $24 = std::shared_ptr<const OSDMap> (expired, weak count 0) = {get() = 0x559cba028000}
  (gdb) print *osdmap
     # pretty sane OSDMap
  (gdb) print sizeof(osdmap)
  $26 = 16
  (gdb) x/2a &osdmap
  0x559ca22acef0:   0x559cba028000  0x559cba0ec900

  (gdb) frame 2
  #2  std::_Sp_counted_base<(__gnu_cxx::_Lock_policy)2>::_M_release (this=0x559cba0ec900) at /usr/include/c++/8/bits/shared_ptr_base.h:148
  148       /usr/include/c++/8/bits/shared_ptr_base.h: No such file or directory.
  (gdb) disassemble
  Dump of assembler code for function std::_Sp_counted_base<(__gnu_cxx::_Lock_policy)2>::_M_release():
  ...
     0x0000559c97675b1e <+62>:      mov    (%rdi),%rax
     0x0000559c97675b21 <+65>:      mov    %rdi,%rbx
     0x0000559c97675b24 <+68>:      callq  *0x10(%rax)
  => 0x0000559c97675b27 <+71>:      test   %rbp,%rbp
  ...
  End of assembler dump.
  (gdb) info registers rdi rbx rax
  rdi            0x559cba0ec900      94131624790272
  rbx            0x559cba0ec900      94131624790272
  rax            0x559cba0ec8a0      94131624790176
  (gdb) x/a 0x559cba0ec8a0 + 0x10
  0x559cba0ec8b0:   0x559cb81c3ea0
  (gdb) bt
  #0  0x0000559cb81c3ea0 in ?? ()
  ...
  (gdb) p $_siginfo._sifields._sigfault.si_addr
  $27 = (void *) 0x559cb81c3ea0
  ```

Helgrind seems to agree:
  ```
  ==00:00:02:54.519 510301== Possible data race during write of size 8 at 0xF123930 by thread ceph#90
  ==00:00:02:54.519 510301== Locks held: 2, at addresses 0xF122A58 0xF1239A8
  ==00:00:02:54.519 510301==    at 0x7218DD: operator= (shared_ptr_base.h:1078)
  ==00:00:02:54.519 510301==    by 0x7218DD: operator= (shared_ptr.h:103)
  ==00:00:02:54.519 510301==    by 0x7218DD: OSD::_committed_osd_maps(unsigned int, unsigned int, MOSDMap*) (OSD.cc:8116)
  ==00:00:02:54.519 510301==    by 0x7752CA: C_OnMapCommit::finish(int) (OSD.cc:7678)
  ==00:00:02:54.519 510301==    by 0x72A06C: Context::complete(int) (Context.h:77)
  ==00:00:02:54.519 510301==    by 0xD07F14: Finisher::finisher_thread_entry() (Finisher.cc:66)
  ==00:00:02:54.519 510301==    by 0xA7E1203: mythread_wrapper (hg_intercepts.c:389)
  ==00:00:02:54.519 510301==    by 0xC6182DD: start_thread (in /usr/lib64/libpthread-2.28.so)
  ==00:00:02:54.519 510301==    by 0xD8B34B2: clone (in /usr/lib64/libc-2.28.so)
  ==00:00:02:54.519 510301==
  ==00:00:02:54.519 510301== This conflicts with a previous read of size 8 by thread ceph#117
  ==00:00:02:54.519 510301== Locks held: 1, at address 0x2123E9A0
  ==00:00:02:54.519 510301==    at 0x6B5842: __shared_ptr (shared_ptr_base.h:1165)
  ==00:00:02:54.519 510301==    by 0x6B5842: shared_ptr (shared_ptr.h:129)
  ==00:00:02:54.519 510301==    by 0x6B5842: get_osdmap (OSD.h:1700)
  ==00:00:02:54.519 510301==    by 0x6B5842: OSD::create_context() (OSD.cc:9053)
  ==00:00:02:54.519 510301==    by 0x71B570: OSD::dequeue_peering_evt(OSDShard*, PG*, std::shared_ptr<PGPeeringEvent>, ThreadPool::TPHandle&) (OSD.cc:9665)
  ==00:00:02:54.519 510301==    by 0x71B997: OSD::dequeue_delete(OSDShard*, PG*, unsigned int, ThreadPool::TPHandle&) (OSD.cc:9701)
  ==00:00:02:54.519 510301==    by 0x70E62E: run (OpSchedulerItem.h:148)
  ==00:00:02:54.519 510301==    by 0x70E62E: OSD::ShardedOpWQ::_process(unsigned int, ceph::heartbeat_handle_d*) (OSD.cc:10677)
  ==00:00:02:54.519 510301==    by 0xD3C093: ShardedThreadPool::shardedthreadpool_worker(unsigned int) (WorkQueue.cc:311)
  ==00:00:02:54.519 510301==    by 0xD3ECF3: ShardedThreadPool::WorkThreadSharded::entry() (WorkQueue.h:706)
  ==00:00:02:54.519 510301==    by 0xA7E1203: mythread_wrapper (hg_intercepts.c:389)
  ==00:00:02:54.519 510301==    by 0xC6182DD: start_thread (in /usr/lib64/libpthread-2.28.so)
  ==00:00:02:54.519 510301==  Address 0xf123930 is 3,824 bytes inside a block of size 10,296 alloc'd
  ==00:00:02:54.519 510301==    at 0xA7DC0C3: operator new[](unsigned long) (vg_replace_malloc.c:433)
  ==00:00:02:54.519 510301==    by 0x66F766: main (ceph_osd.cc:688)
  ==00:00:02:54.519 510301==  Block was alloc'd by thread #1
  ```

Actually there is plenty of similar issues reported like:
  ```
  ==00:00:05:04.903 510301== Possible data race during read of size 8 at 0x1E3E0588 by thread ceph#119
  ==00:00:05:04.903 510301== Locks held: 1, at address 0x1EAD41D0
  ==00:00:05:04.903 510301==    at 0x753165: clear (hashtable.h:2051)
  ==00:00:05:04.903 510301==    by 0x753165: std::_Hashtable<entity_addr_t, std::pair<entity_addr_t const, utime_t>, mempool::pool_allocator<(mempool::pool_index_t)15, std::pair<entity_addr_t const, utime_t>
  >, std::__detail::_Select1st, std::equal_to<entity_addr_t>, std::hash<entity_addr_t>, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__deta
  il::_Hashtable_traits<true, false, true> >::~_Hashtable() (hashtable.h:1369)
  ==00:00:05:04.903 510301==    by 0x75331C: ~unordered_map (unordered_map.h:102)
  ==00:00:05:04.903 510301==    by 0x75331C: OSDMap::~OSDMap() (OSDMap.h:350)
  ==00:00:05:04.903 510301==    by 0x753606: operator() (shared_cache.hpp:100)
  ==00:00:05:04.903 510301==    by 0x753606: std::_Sp_counted_deleter<OSDMap const*, SharedLRU<unsigned int, OSDMap const>::Cleanup, std::allocator<void>, (__gnu_cxx::_Lock_policy)2>::_M_dispose() (shared_ptr
  _base.h:471)
  ==00:00:05:04.903 510301==    by 0x73BB26: _M_release (shared_ptr_base.h:155)
  ==00:00:05:04.903 510301==    by 0x73BB26: std::_Sp_counted_base<(__gnu_cxx::_Lock_policy)2>::_M_release() (shared_ptr_base.h:148)
  ==00:00:05:04.903 510301==    by 0x6B58A9: ~__shared_count (shared_ptr_base.h:728)
  ==00:00:05:04.903 510301==    by 0x6B58A9: ~__shared_ptr (shared_ptr_base.h:1167)
  ==00:00:05:04.903 510301==    by 0x6B58A9: ~shared_ptr (shared_ptr.h:103)
  ==00:00:05:04.903 510301==    by 0x6B58A9: OSD::create_context() (OSD.cc:9053)
  ==00:00:05:04.903 510301==    by 0x71B570: OSD::dequeue_peering_evt(OSDShard*, PG*, std::shared_ptr<PGPeeringEvent>, ThreadPool::TPHandle&) (OSD.cc:9665)
  ==00:00:05:04.903 510301==    by 0x71B997: OSD::dequeue_delete(OSDShard*, PG*, unsigned int, ThreadPool::TPHandle&) (OSD.cc:9701)
  ==00:00:05:04.903 510301==    by 0x70E62E: run (OpSchedulerItem.h:148)
  ==00:00:05:04.903 510301==    by 0x70E62E: OSD::ShardedOpWQ::_process(unsigned int, ceph::heartbeat_handle_d*) (OSD.cc:10677)
  ==00:00:05:04.903 510301==    by 0xD3C093: ShardedThreadPool::shardedthreadpool_worker(unsigned int) (WorkQueue.cc:311)
  ==00:00:05:04.903 510301==    by 0xD3ECF3: ShardedThreadPool::WorkThreadSharded::entry() (WorkQueue.h:706)
  ==00:00:05:04.903 510301==    by 0xA7E1203: mythread_wrapper (hg_intercepts.c:389)
  ==00:00:05:04.903 510301==    by 0xC6182DD: start_thread (in /usr/lib64/libpthread-2.28.so)
  ==00:00:05:04.903 510301==    by 0xD8B34B2: clone (in /usr/lib64/libc-2.28.so)
  ==00:00:05:04.903 510301==
  ==00:00:05:04.903 510301== This conflicts with a previous write of size 8 by thread ceph#90
  ==00:00:05:04.903 510301== Locks held: 2, at addresses 0xF122A58 0xF1239A8
  ==00:00:05:04.903 510301==    at 0x7531E1: clear (hashtable.h:2054)
  ==00:00:05:04.903 510301==    by 0x7531E1: std::_Hashtable<entity_addr_t, std::pair<entity_addr_t const, utime_t>, mempool::pool_allocator<(mempool::pool_index_t)15, std::pair<entity_addr_t const, utime_t> >, std::__detail::_Select1st, std::equal_to<entity_addr_t>, std::hash<entity_addr_t>, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<true, false, true> >::~_Hashtable() (hashtable.h:1369)
  ==00:00:05:04.903 510301==    by 0x75331C: ~unordered_map (unordered_map.h:102)
  ==00:00:05:04.903 510301==    by 0x75331C: OSDMap::~OSDMap() (OSDMap.h:350)
  ==00:00:05:04.903 510301==    by 0x753606: operator() (shared_cache.hpp:100)
  ==00:00:05:04.903 510301==    by 0x753606: std::_Sp_counted_deleter<OSDMap const*, SharedLRU<unsigned int, OSDMap const>::Cleanup, std::allocator<void>, (__gnu_cxx::_Lock_policy)2>::_M_dispose() (shared_ptr_base.h:471)
  ==00:00:05:04.903 510301==    by 0x73BB26: _M_release (shared_ptr_base.h:155)
  ==00:00:05:04.903 510301==    by 0x73BB26: std::_Sp_counted_base<(__gnu_cxx::_Lock_policy)2>::_M_release() (shared_ptr_base.h:148)
  ==00:00:05:04.903 510301==    by 0x72191E: operator= (shared_ptr_base.h:747)
  ==00:00:05:04.903 510301==    by 0x72191E: operator= (shared_ptr_base.h:1078)
  ==00:00:05:04.903 510301==    by 0x72191E: operator= (shared_ptr.h:103)
  ==00:00:05:04.903 510301==    by 0x72191E: OSD::_committed_osd_maps(unsigned int, unsigned int, MOSDMap*) (OSD.cc:8116)
  ==00:00:05:04.903 510301==    by 0x7752CA: C_OnMapCommit::finish(int) (OSD.cc:7678)
  ==00:00:05:04.903 510301==    by 0x72A06C: Context::complete(int) (Context.h:77)
  ==00:00:05:04.903 510301==    by 0xD07F14: Finisher::finisher_thread_entry() (Finisher.cc:66)
  ==00:00:05:04.903 510301==  Address 0x1e3e0588 is 872 bytes inside a block of size 1,208 alloc'd
  ==00:00:05:04.903 510301==    at 0xA7DC0C3: operator new[](unsigned long) (vg_replace_malloc.c:433)
  ==00:00:05:04.903 510301==    by 0x6C7C0C: OSDService::try_get_map(unsigned int) (OSD.cc:1606)
  ==00:00:05:04.903 510301==    by 0x7213BD: get_map (OSD.h:699)
  ==00:00:05:04.903 510301==    by 0x7213BD: get_map (OSD.h:1732)
  ==00:00:05:04.903 510301==    by 0x7213BD: OSD::_committed_osd_maps(unsigned int, unsigned int, MOSDMap*) (OSD.cc:8076)
  ==00:00:05:04.903 510301==    by 0x7752CA: C_OnMapCommit::finish(int) (OSD.cc:7678)
  ==00:00:05:04.903 510301==    by 0x72A06C: Context::complete(int) (Context.h:77)
  ==00:00:05:04.903 510301==    by 0xD07F14: Finisher::finisher_thread_entry() (Finisher.cc:66)
  ==00:00:05:04.903 510301==    by 0xA7E1203: mythread_wrapper (hg_intercepts.c:389)
  ==00:00:05:04.903 510301==    by 0xC6182DD: start_thread (in /usr/lib64/libpthread-2.28.so)
  ==00:00:05:04.903 510301==    by 0xD8B34B2: clone (in /usr/lib64/libc-2.28.so)
  ```

Signed-off-by: Radoslaw Zarzynski <rzarzyns@redhat.com>
(cherry picked from commit 80da5f9)

Conflicts:
	src/osd/OSD.cc in
		bool OSD::asok_command
		int OSD::shutdown
		void OSD::maybe_update_heartbeat_peers
		void OSD::_preboot
		void OSD::queue_want_up_thru
		void OSD::send_alive
		void OSD::send_failures
		void OSD::send_beacon
		MPGStats* OSD::collect_pg_stats
		void OSD::note_down_osd
		void OSD::consume_map
		void OSD::activate_map
	src/osd/OSD.h in
		private: dispatch_session_waiting

- also use the new const OSDMapRef in places that no longer exist in master
	src/osd/OSD.cc in
		void OSDService::share_map
		void OSDService::send_incremental_map
		int OSD::_do_command
		void OSD::note_up_osd
		int OSD::init_op_flags
	src/osd/OSD.h in
		void send_incremental_map
		void share_map