diff --git a/changes/bug9108 b/changes/bug9108
new file mode 100644
index 0000000000..9d2d3d8b65
--- /dev/null
+++ b/changes/bug9108
@@ -0,0 +1,3 @@
+  o Code simplifications and refactoring:
+    - Make global_circuitlist data structure in circuitlist.c
+      a doubly-linked list. Bug #9108.
diff --git a/src/or/channel.h b/src/or/channel.h
index bd99ebc933..430a0251a2 100644
--- a/src/or/channel.h
+++ b/src/or/channel.h
@@ -10,7 +10,6 @@
 #define TOR_CHANNEL_H
 
 #include "or.h"
-#include "tor_queue.h"
 #include "circuitmux.h"
 
 /* Channel handler function pointer typedefs */
diff --git a/src/or/circuitbuild.c b/src/or/circuitbuild.c
index 43d2ffe4db..0b5a8556c9 100644
--- a/src/or/circuitbuild.c
+++ b/src/or/circuitbuild.c
@@ -46,13 +46,6 @@
 #define MIN(a,b) ((a)<(b)?(a):(b))
 #endif
 
-/********* START VARIABLES **********/
-
-/** A global list of all circuits at this hop. */
-extern circuit_t *global_circuitlist;
-
-/********* END VARIABLES ************/
-
 static channel_t * channel_connect_for_circuit(const tor_addr_t *addr,
                                                uint16_t port,
                                                const char *id_digest);
@@ -2181,7 +2174,7 @@ pathbias_count_circs_in_states(entry_guard_t *guard,
   int open_circuits = 0;
 
   /* Count currently open circuits. Give them the benefit of the doubt. */
-  for (circ = global_circuitlist; circ; circ = circ->next) {
+  TOR_LIST_FOREACH(circ, circuit_get_global_list_(), head) {
     origin_circuit_t *ocirc = NULL;
     if (!CIRCUIT_IS_ORIGIN(circ) || /* didn't originate here */
         circ->marked_for_close) /* already counted */
diff --git a/src/or/circuitlist.c b/src/or/circuitlist.c
index 85bacce485..a4144e8000 100644
--- a/src/or/circuitlist.c
+++ b/src/or/circuitlist.c
@@ -36,7 +36,8 @@
 /********* START VARIABLES **********/
 
 /** A global list of all circuits at this hop. */
-circuit_t *global_circuitlist=NULL;
+struct global_circuitlist_s global_circuitlist =
+  TOR_LIST_HEAD_INITIALIZER(global_circuitlist);
 
 /** A list of all the circuits in CIRCUIT_STATE_CHAN_WAIT. */
 static smartlist_t *circuits_pending_chans = NULL;
@@ -369,21 +370,6 @@ circuit_set_state(circuit_t *circ, uint8_t state)
   circ->state = state;
 }
 
-/** Add <b>circ</b> to the global list of circuits. This is called only from
- * within circuit_new.
- */
-static void
-circuit_add(circuit_t *circ)
-{
-  if (!global_circuitlist) { /* first one */
-    global_circuitlist = circ;
-    circ->next = NULL;
-  } else {
-    circ->next = global_circuitlist;
-    global_circuitlist = circ;
-  }
-}
-
 /** Append to <b>out</b> all circuits in state CHAN_WAIT waiting for
  * the given connection. */
 void
@@ -441,33 +427,17 @@ circuit_count_pending_on_channel(channel_t *chan)
 void
 circuit_close_all_marked(void)
 {
-  circuit_t *tmp,*m;
-
-  while (global_circuitlist && global_circuitlist->marked_for_close) {
-    tmp = global_circuitlist->next;
-    circuit_free(global_circuitlist);
-    global_circuitlist = tmp;
-  }
-
-  tmp = global_circuitlist;
-  while (tmp && tmp->next) {
-    if (tmp->next->marked_for_close) {
-      m = tmp->next->next;
-      circuit_free(tmp->next);
-      tmp->next = m;
-      /* Need to check new tmp->next; don't advance tmp. */
-    } else {
-      /* Advance tmp. */
-      tmp = tmp->next;
-    }
-  }
+  circuit_t *circ, *tmp;
+  TOR_LIST_FOREACH_SAFE(circ, &global_circuitlist, head, tmp)
+    if (circ->marked_for_close)
+      circuit_free(circ);
 }
 
 /** Return the head of the global linked list of circuits. */
-circuit_t *
+struct global_circuitlist_s *
 circuit_get_global_list_(void)
 {
-  return global_circuitlist;
+  return &global_circuitlist;
 }
 
 /** Function to make circ-\>state human-readable */
@@ -684,7 +654,7 @@ init_circuit_base(circuit_t *circ)
   circ->deliver_window = CIRCWINDOW_START;
   cell_queue_init(&circ->n_chan_cells);
 
-  circuit_add(circ);
+  TOR_LIST_INSERT_HEAD(&global_circuitlist, circ, head);
 }
 
 /** Allocate space for a new circuit, initializing with <b>p_circ_id</b>
@@ -803,6 +773,8 @@ circuit_free(circuit_t *circ)
   extend_info_free(circ->n_hop);
   tor_free(circ->n_chan_create_cell);
 
+  TOR_LIST_REMOVE(circ, head);
+
   /* Remove from map. */
   circuit_set_n_circid_chan(circ, 0, NULL);
 
@@ -838,11 +810,11 @@ circuit_free_cpath(crypt_path_t *cpath)
 void
 circuit_free_all(void)
 {
-  circuit_t *next;
-  while (global_circuitlist) {
-    next = global_circuitlist->next;
-    if (! CIRCUIT_IS_ORIGIN(global_circuitlist)) {
-      or_circuit_t *or_circ = TO_OR_CIRCUIT(global_circuitlist);
+  circuit_t *tmp, *tmp2;
+
+  TOR_LIST_FOREACH_SAFE(tmp, &global_circuitlist, head, tmp2) {
+    if (! CIRCUIT_IS_ORIGIN(tmp)) {
+      or_circuit_t *or_circ = TO_OR_CIRCUIT(tmp);
       while (or_circ->resolving_streams) {
         edge_connection_t *next_conn;
         next_conn = or_circ->resolving_streams->next_stream;
@@ -850,8 +822,7 @@ circuit_free_all(void)
         or_circ->resolving_streams = next_conn;
       }
     }
-    circuit_free(global_circuitlist);
-    global_circuitlist = next;
+    circuit_free(tmp);
   }
 
   smartlist_free(circuits_pending_chans);
@@ -921,7 +892,7 @@ circuit_dump_by_conn(connection_t *conn, int severity)
   circuit_t *circ;
   edge_connection_t *tmpconn;
 
-  for (circ = global_circuitlist; circ; circ = circ->next) {
+  TOR_LIST_FOREACH(circ, &global_circuitlist, head) {
     circid_t n_circ_id = circ->n_circ_id, p_circ_id = 0;
 
     if (circ->marked_for_close) {
@@ -985,7 +956,7 @@ circuit_dump_by_chan(channel_t *chan, int severity)
 
   tor_assert(chan);
 
-  for (circ = global_circuitlist; circ; circ = circ->next) {
+  TOR_LIST_FOREACH(circ, &global_circuitlist, head) {
     circid_t n_circ_id = circ->n_circ_id, p_circ_id = 0;
 
     if (circ->marked_for_close) {
@@ -1026,7 +997,7 @@ origin_circuit_t *
 circuit_get_by_global_id(uint32_t id)
 {
   circuit_t *circ;
-  for (circ=global_circuitlist;circ;circ = circ->next) {
+  TOR_LIST_FOREACH(circ, &global_circuitlist, head) {
     if (CIRCUIT_IS_ORIGIN(circ) &&
         TO_ORIGIN_CIRCUIT(circ)->global_identifier == id) {
       if (circ->marked_for_close)
@@ -1089,7 +1060,7 @@ circuit_get_by_circid_channel_impl(circid_t circ_id, channel_t *chan,
   /* We comment it out because coverity complains otherwise.
   {
     circuit_t *circ;
-    for (circ=global_circuitlist;circ;circ = circ->next) {
+    TOR_LIST_FOREACH(circ, &global_circuitlist, head) {
       if (! CIRCUIT_IS_ORIGIN(circ)) {
         or_circuit_t *or_circ = TO_OR_CIRCUIT(circ);
         if (or_circ->p_chan == chan && or_circ->p_circ_id == circ_id) {
@@ -1171,7 +1142,7 @@ circuit_unlink_all_from_channel(channel_t *chan, int reason)
 
   channel_unlink_all_circuits(chan);
 
-  for (circ = global_circuitlist; circ; circ = circ->next) {
+  TOR_LIST_FOREACH(circ, &global_circuitlist, head) {
     int mark = 0;
     if (circ->n_chan == chan) {
       circuit_set_n_circid_chan(circ, 0, NULL);
@@ -1207,8 +1178,7 @@ origin_circuit_t *
 circuit_get_ready_rend_circ_by_rend_data(const rend_data_t *rend_data)
 {
   circuit_t *circ;
-
-  for (circ = global_circuitlist; circ; circ = circ->next) {
+  TOR_LIST_FOREACH(circ, &global_circuitlist, head) {
     if (!circ->marked_for_close &&
         circ->purpose == CIRCUIT_PURPOSE_C_REND_READY) {
       origin_circuit_t *ocirc = TO_ORIGIN_CIRCUIT(circ);
@@ -1236,11 +1206,11 @@ circuit_get_next_by_pk_and_purpose(origin_circuit_t *start,
   circuit_t *circ;
   tor_assert(CIRCUIT_PURPOSE_IS_ORIGIN(purpose));
   if (start == NULL)
-    circ = global_circuitlist;
+    circ = TOR_LIST_FIRST(&global_circuitlist);
   else
-    circ = TO_CIRCUIT(start)->next;
+    circ = TOR_LIST_NEXT(TO_CIRCUIT(start), head);
 
-  for ( ; circ; circ = circ->next) {
+  for ( ; circ; circ = TOR_LIST_NEXT(circ, head)) {
     if (circ->marked_for_close)
       continue;
     if (circ->purpose != purpose)
@@ -1263,7 +1233,7 @@ circuit_get_by_rend_token_and_purpose(uint8_t purpose, const char *token,
                                       size_t len)
 {
   circuit_t *circ;
-  for (circ = global_circuitlist; circ; circ = circ->next) {
+  TOR_LIST_FOREACH(circ, &global_circuitlist, head) {
     if (! circ->marked_for_close &&
         circ->purpose == purpose &&
         tor_memeq(TO_OR_CIRCUIT(circ)->rend_token, token, len))
@@ -1325,7 +1295,7 @@ circuit_find_to_cannibalize(uint8_t purpose, extend_info_t *info,
             "capacity %d, internal %d",
             purpose, need_uptime, need_capacity, internal);
 
-  for (circ_=global_circuitlist; circ_; circ_ = circ_->next) {
+  TOR_LIST_FOREACH(circ_, &global_circuitlist, head) {
     if (CIRCUIT_IS_ORIGIN(circ_) &&
         circ_->state == CIRCUIT_STATE_OPEN &&
         !circ_->marked_for_close &&
@@ -1415,8 +1385,7 @@ void
 circuit_mark_all_unused_circs(void)
 {
   circuit_t *circ;
-
-  for (circ=global_circuitlist; circ; circ = circ->next) {
+  TOR_LIST_FOREACH(circ, &global_circuitlist, head) {
     if (CIRCUIT_IS_ORIGIN(circ) &&
         !circ->marked_for_close &&
         !circ->timestamp_dirty)
@@ -1435,8 +1404,7 @@ void
 circuit_mark_all_dirty_circs_as_unusable(void)
 {
   circuit_t *circ;
-
-  for (circ=global_circuitlist; circ; circ = circ->next) {
+  TOR_LIST_FOREACH(circ, &global_circuitlist, head) {
     if (CIRCUIT_IS_ORIGIN(circ) &&
         !circ->marked_for_close &&
         circ->timestamp_dirty) {
@@ -1698,7 +1666,7 @@ circuits_handle_oom(size_t current_allocation)
 
   /* This algorithm itself assumes that you've got enough memory slack
    * to actually run it. */
-  for (circ = global_circuitlist; circ; circ = circ->next)
+  TOR_LIST_FOREACH(circ, &global_circuitlist, head)
     smartlist_add(circlist, circ);
 
   /* This is O(n log n); there are faster algorithms we could use instead.
diff --git a/src/or/circuitlist.h b/src/or/circuitlist.h
index 4e56f5264f..a43315d238 100644
--- a/src/or/circuitlist.h
+++ b/src/or/circuitlist.h
@@ -14,7 +14,9 @@
 
 #include "testsupport.h"
 
-circuit_t * circuit_get_global_list_(void);
+TOR_LIST_HEAD(global_circuitlist_s, circuit_t);
+
+struct global_circuitlist_s* circuit_get_global_list_(void);
 const char *circuit_state_to_string(int state);
 const char *circuit_purpose_to_controller_string(uint8_t purpose);
 const char *circuit_purpose_to_controller_hs_state_string(uint8_t purpose);
diff --git a/src/or/circuituse.c b/src/or/circuituse.c
index 8fb70f5853..fdafa3fbf1 100644
--- a/src/or/circuituse.c
+++ b/src/or/circuituse.c
@@ -31,12 +31,6 @@
 #include "router.h"
 #include "routerlist.h"
 
-/********* START VARIABLES **********/
-
-extern circuit_t *global_circuitlist; /* from circuitlist.c */
-
-/********* END VARIABLES ************/
-
 static void circuit_expire_old_circuits_clientside(void);
 static void circuit_increment_failure_count(void);
 
@@ -286,7 +280,7 @@ circuit_get_best(const entry_connection_t *conn,
 
   tor_gettimeofday(&now);
 
-  for (circ=global_circuitlist;circ;circ = circ->next) {
+  TOR_LIST_FOREACH(circ, circuit_get_global_list_(), head) {
     origin_circuit_t *origin_circ;
     if (!CIRCUIT_IS_ORIGIN(circ))
       continue;
@@ -327,7 +321,7 @@ count_pending_general_client_circuits(void)
 
   int count = 0;
 
-  for (circ = global_circuitlist; circ; circ = circ->next) {
+  TOR_LIST_FOREACH(circ, circuit_get_global_list_(), head) {
     if (circ->marked_for_close ||
         circ->state == CIRCUIT_STATE_OPEN ||
         circ->purpose != CIRCUIT_PURPOSE_C_GENERAL ||
@@ -375,7 +369,7 @@ circuit_conforms_to_options(const origin_circuit_t *circ,
 void
 circuit_expire_building(void)
 {
-  circuit_t *victim, *next_circ = global_circuitlist;
+  circuit_t *victim, *next_circ;
   /* circ_times.timeout_ms and circ_times.close_ms are from
    * circuit_build_times_get_initial_timeout() if we haven't computed
    * custom timeouts yet */
@@ -393,10 +387,9 @@ circuit_expire_building(void)
    * we want to be more lenient with timeouts, in case the
    * user has relocated and/or changed network connections.
    * See bug #3443. */
-  while (next_circ) {
+  TOR_LIST_FOREACH(next_circ, circuit_get_global_list_(), head) {
     if (!CIRCUIT_IS_ORIGIN(next_circ) || /* didn't originate here */
         next_circ->marked_for_close) { /* don't mess with marked circs */
-      next_circ = next_circ->next;
       continue;
     }
 
@@ -408,9 +401,7 @@ circuit_expire_building(void)
       any_opened_circs = 1;
       break;
     }
-    next_circ = next_circ->next;
   }
-  next_circ = global_circuitlist;
 
 #define SET_CUTOFF(target, msec) do {                       \
     long ms = tor_lround(msec);                             \
@@ -481,10 +472,9 @@ circuit_expire_building(void)
              MAX(circ_times.close_ms*2 + 1000,
                  options->SocksTimeout * 1000));
 
-  while (next_circ) {
+  TOR_LIST_FOREACH(next_circ, circuit_get_global_list_(), head) {
     struct timeval cutoff;
     victim = next_circ;
-    next_circ = next_circ->next;
     if (!CIRCUIT_IS_ORIGIN(victim) || /* didn't originate here */
         victim->marked_for_close)     /* don't mess with marked circs */
       continue;
@@ -818,7 +808,7 @@ circuit_stream_is_being_handled(entry_connection_t *conn,
                                    get_options()->LongLivedPorts,
                                    conn ? conn->socks_request->port : port);
 
-  for (circ=global_circuitlist;circ;circ = circ->next) {
+  TOR_LIST_FOREACH(circ, circuit_get_global_list_(), head) {
     if (CIRCUIT_IS_ORIGIN(circ) &&
         !circ->marked_for_close &&
         circ->purpose == CIRCUIT_PURPOSE_C_GENERAL &&
@@ -869,7 +859,7 @@ circuit_predict_and_launch_new(void)
   int flags = 0;
 
   /* First, count how many of each type of circuit we have already. */
-  for (circ=global_circuitlist;circ;circ = circ->next) {
+  TOR_LIST_FOREACH(circ, circuit_get_global_list_(), head) {
     cpath_build_state_t *build_state;
     origin_circuit_t *origin_circ;
     if (!CIRCUIT_IS_ORIGIN(circ))
@@ -1093,7 +1083,7 @@ circuit_expire_old_circuits_clientside(void)
     cutoff.tv_sec -= get_options()->CircuitIdleTimeout;
   }
 
-  for (circ = global_circuitlist; circ; circ = circ->next) {
+  TOR_LIST_FOREACH(circ, circuit_get_global_list_(), head) {
     if (circ->marked_for_close || !CIRCUIT_IS_ORIGIN(circ))
       continue;
     /* If the circuit has been dirty for too long, and there are no streams
@@ -1176,7 +1166,7 @@ circuit_expire_old_circuits_serverside(time_t now)
   or_circuit_t *or_circ;
   time_t cutoff = now - IDLE_ONE_HOP_CIRC_TIMEOUT;
 
-  for (circ = global_circuitlist; circ; circ = circ->next) {
+  TOR_LIST_FOREACH(circ, circuit_get_global_list_(), head) {
     if (circ->marked_for_close || CIRCUIT_IS_ORIGIN(circ))
       continue;
     or_circ = TO_OR_CIRCUIT(circ);
@@ -1223,7 +1213,7 @@ circuit_enough_testing_circs(void)
   if (have_performed_bandwidth_test)
     return 1;
 
-  for (circ = global_circuitlist; circ; circ = circ->next) {
+  TOR_LIST_FOREACH(circ, circuit_get_global_list_(), head) {
     if (!circ->marked_for_close && CIRCUIT_IS_ORIGIN(circ) &&
         circ->purpose == CIRCUIT_PURPOSE_TESTING &&
         circ->state == CIRCUIT_STATE_OPEN)
diff --git a/src/or/control.c b/src/or/control.c
index 03b42af539..d624d28798 100644
--- a/src/or/control.c
+++ b/src/or/control.c
@@ -1928,7 +1928,7 @@ getinfo_helper_events(control_connection_t *control_conn,
   if (!strcmp(question, "circuit-status")) {
     circuit_t *circ_;
     smartlist_t *status = smartlist_new();
-    for (circ_ = circuit_get_global_list_(); circ_; circ_ = circ_->next) {
+    TOR_LIST_FOREACH(circ_, circuit_get_global_list_(), head) {
       origin_circuit_t *circ;
       char *circdesc;
       const char *state;
diff --git a/src/or/onion.c b/src/or/onion.c
index d4a65022fc..5542854cf7 100644
--- a/src/or/onion.c
+++ b/src/or/onion.c
@@ -21,7 +21,6 @@
 #include "relay.h"
 #include "rephist.h"
 #include "router.h"
-#include "tor_queue.h"
 
 /** Type for a linked list of circuits that are waiting for a free CPU worker
  * to process a waiting onion handshake. */
diff --git a/src/or/or.h b/src/or/or.h
index d2f6953ab3..2daf12b82d 100644
--- a/src/or/or.h
+++ b/src/or/or.h
@@ -2904,7 +2904,8 @@ typedef struct circuit_t {
   /** Unique ID for measuring tunneled network status requests. */
   uint64_t dirreq_id;
 
-  struct circuit_t *next; /**< Next circuit in linked list of all circuits. */
+  /** Next circuit in linked list of all circuits (global_circuitlist). */
+  TOR_LIST_ENTRY(circuit_t) head;
 
   /** Next circuit in the doubly-linked ring of circuits waiting to add
    * cells to n_conn.  NULL if we have no cells pending, or if we're not
diff --git a/src/or/relay.c b/src/or/relay.c
index 297f0f69e0..9a0fdd9631 100644
--- a/src/or/relay.c
+++ b/src/or/relay.c
@@ -2113,7 +2113,7 @@ dump_cell_pool_usage(int severity)
   circuit_t *c;
   int n_circs = 0;
   int n_cells = 0;
-  for (c = circuit_get_global_list_(); c; c = c->next) {
+  TOR_LIST_FOREACH(c, circuit_get_global_list_(), head) {
     n_cells += c->n_chan_cells.n;
     if (!CIRCUIT_IS_ORIGIN(c))
       n_cells += TO_OR_CIRCUIT(c)->p_chan_cells.n;
diff --git a/src/or/rendclient.c b/src/or/rendclient.c
index 7115bf2080..ea4512d091 100644
--- a/src/or/rendclient.c
+++ b/src/or/rendclient.c
@@ -358,7 +358,7 @@ rend_client_close_other_intros(const char *onion_address)
 {
   circuit_t *c;
   /* abort parallel intro circs, if any */
-  for (c = circuit_get_global_list_(); c; c = c->next) {
+  TOR_LIST_FOREACH(c, circuit_get_global_list_(), head) {
     if ((c->purpose == CIRCUIT_PURPOSE_C_INTRODUCING ||
         c->purpose == CIRCUIT_PURPOSE_C_INTRODUCE_ACK_WAIT) &&
         !c->marked_for_close && CIRCUIT_IS_ORIGIN(c)) {
diff --git a/src/or/rendservice.c b/src/or/rendservice.c
index 2e93fc3f54..fb56dc0360 100644
--- a/src/or/rendservice.c
+++ b/src/or/rendservice.c
@@ -543,7 +543,7 @@ rend_config_services(const or_options_t *options, int validate_only)
     /* XXXX it would be nicer if we had a nicer abstraction to use here,
      * so we could just iterate over the list of services to close, but
      * once again, this isn't critical-path code. */
-    for (circ = circuit_get_global_list_(); circ; circ = circ->next) {
+    TOR_LIST_FOREACH(circ, circuit_get_global_list_(), head) {
       if (!circ->marked_for_close &&
           circ->state == CIRCUIT_STATE_OPEN &&
           (circ->purpose == CIRCUIT_PURPOSE_S_ESTABLISH_INTRO ||
@@ -2375,7 +2375,7 @@ count_established_intro_points(const char *query)
 {
   int num_ipos = 0;
   circuit_t *circ;
-  for (circ = circuit_get_global_list_(); circ; circ = circ->next) {
+  TOR_LIST_FOREACH(circ, circuit_get_global_list_(), head) {
     if (!circ->marked_for_close &&
         circ->state == CIRCUIT_STATE_OPEN &&
         (circ->purpose == CIRCUIT_PURPOSE_S_ESTABLISH_INTRO ||
diff --git a/src/or/rephist.c b/src/or/rephist.c
index c84322a679..0943a3434a 100644
--- a/src/or/rephist.c
+++ b/src/or/rephist.c
@@ -2599,7 +2599,7 @@ rep_hist_buffer_stats_write(time_t now)
     goto done; /* Not ready to write */
 
   /* Add open circuits to the history. */
-  for (circ = circuit_get_global_list_(); circ; circ = circ->next) {
+  TOR_LIST_FOREACH(circ, circuit_get_global_list_(), head) {
     rep_hist_buffer_stats_add_circ(circ, now);
   }
 
diff --git a/src/or/status.c b/src/or/status.c
index d239e6ee75..6fe2f67bf4 100644
--- a/src/or/status.c
+++ b/src/or/status.c
@@ -23,7 +23,7 @@ count_circuits(void)
   circuit_t *circ;
   int nr=0;
 
-  for (circ = circuit_get_global_list_(); circ; circ = circ->next)
+  TOR_LIST_FOREACH(circ, circuit_get_global_list_(), head)
     nr++;
 
   return nr;