osdc/Objecter: fix recursive locking in _finish_command

The path

#9  Objecter::_finish_command (this=this@entry=0x7f76c00aeb30, c=c@entry=0x7f76b0000b10, r=<optimized out>, rs="osd down") at /build/ceph-13.0.2-1932-g458b4fb/src/osdc/Objecter.cc:4950
#10 0x00007f76d26de106 in Objecter::_check_command_map_dne (this=this@entry=0x7f76c00aeb30, c=c@entry=0x7f76b0000b10) at /build/ceph-13.0.2-1932-g458b4fb/src/osdc/Objecter.cc:1726
#11 0x00007f76d26e52e4 in Objecter::_scan_requests (this=this@entry=0x7f76c00aeb30, s=0x7f76c00af8a0, skipped_map=skipped_map@entry=false, cluster_full=cluster_full@entry=false, pool_full_map=0x7f76be7fb330, need_resend=..., need_resend_linger=..., need_resend_command=std::map with 0 elements, sul=...,
    gap_removed_snaps=0x7f76ac0016f8) at /build/ceph-13.0.2-1932-g458b4fb/src/osdc/Objecter.cc:1120
#12 0x00007f76d26eded5 in Objecter::handle_osd_map (this=this@entry=0x7f76c00aeb30, m=m@entry=0x7f76ac0014a0) at /build/ceph-13.0.2-1932-g458b4fb/src/osdc/Objecter.cc:1228

led to recursive lock of the session mutex (locked in _scan_requests,
and again in _finish_command).

Fix by making the callers for _finish_command (and
_check_command_map_dne) take the session lock.

Fixes: http://tracker.ceph.com/issues/23940
Signed-off-by: Sage Weil <sage@redhat.com>

src/osdc/Objecter.cc

@@ -1708,14 +1708,17 @@ void Objecter::C_Command_Map_Latest::finish(int r)
   if (c->map_dne_bound == 0)
     c->map_dne_bound = latest;
 
+  OSDSession::unique_lock sul(c->session->lock);
   objecter->_check_command_map_dne(c);
+  sul.unlock();
 
   c->put();
 }
 
 void Objecter::_check_command_map_dne(CommandOp *c)
 {
   // rwlock is locked unique
+  // session is locked unique
 
   ldout(cct, 10) << "_check_command_map_dne tid " << c->tid
 		 << " current " << osdmap->get_epoch()
@@ -1733,6 +1736,7 @@ void Objecter::_check_command_map_dne(CommandOp *c)
 void Objecter::_send_command_map_check(CommandOp *c)
 {
   // rwlock is locked unique
+  // session is locked unique
 
   // ask the monitor
   if (check_latest_map_commands.count(c->tid) == 0) {
@@ -4781,8 +4785,10 @@ void Objecter::handle_command_reply(MCommandReply *m)
 
   sl.unlock();
 
-
+  OSDSession::unique_lock sul(s->lock);
   _finish_command(c, m->r, m->rs);
+  sul.unlock();
+
   m->put();
   s->put();
 }
@@ -4928,13 +4934,16 @@ int Objecter::command_op_cancel(OSDSession *s, ceph_tid_t tid, int r)
 
   CommandOp *op = it->second;
   _command_cancel_map_check(op);
+  OSDSession::unique_lock sl(op->session->lock);
   _finish_command(op, r, "");
+  sl.unlock();
   return 0;
 }
 
 void Objecter::_finish_command(CommandOp *c, int r, string rs)
 {
   // rwlock is locked unique
+  // session lock is locked
 
   ldout(cct, 10) << "_finish_command " << c->tid << " = " << r << " "
 		 << rs << dendl;
@@ -4947,9 +4956,7 @@ void Objecter::_finish_command(CommandOp *c, int r, string rs)
     timer.cancel_event(c->ontimeout);
 
   OSDSession *s = c->session;
-  OSDSession::unique_lock sl(s->lock);
   _session_command_op_remove(c->session, c);
-  sl.unlock();
 
   c->put();