--- os/unix/unixd.c	(revision 1809833)
+++ os/unix/unixd.c	(working copy)
@@ -582,7 +582,44 @@ AP_DECLARE(void) ap_unixd_mpm_set_signals(apr_pool
                               apr_pool_cleanup_null);
 }
 
+static int ap_unixd_mpm_query(int query_code, int *result, apr_status_t *rv)
+{
+    if (retained_data && retained_data->mpm_query_fn) {
+        return retained_data->mpm_query_fn(query_code, result, rv);
+    }
+    else {
+        return DECLINED;
+    }
+}
 
+static apr_status_t ap_unixd_mpm_query_cleanup(void *fn)
+{
+    if (retained_data && retained_data->mpm_query_fn == fn) {
+        retained_data->mpm_query_fn = NULL;
+    }
+    return APR_SUCCESS;
+}
+
+/* To cope with restarts (when the mpm_query function may have been unloaded
+ * with the DSO), we register the hook once and keep/clear the current function
+ * in retained_data->mpm_query_fn, according to the pconf's lifetime.
+ */
+AP_DECLARE(void) ap_unixd_hook_mpm_query(apr_pool_t *pconf,
+                                         int (*fn)(int, int*, apr_status_t*))
+{
+    void *once = NULL;
+    apr_pool_userdata_get(&once, "ap_unixd_hook_mpm_query", pconf);
+    if (!once) {
+        AP_DEBUG_ASSERT(pconf == apr_hook_global_pool);
+        apr_pool_userdata_setn("true", "ap_unixd_hook_mpm_query", NULL, pconf);
+        ap_hook_mpm_query(ap_unixd_mpm_query, NULL, NULL, APR_HOOK_MIDDLE);
+    }
+
+    ap_unixd_mpm_get_retained_data()->mpm_query_fn = fn;
+    apr_pool_cleanup_register(pconf, fn, ap_unixd_mpm_query_cleanup,
+                              apr_pool_cleanup_null);
+}
+
 #ifdef _OSD_POSIX
 
 #include "apr_lib.h"
--- os/unix/unixd.h	(revision 1809833)
+++ os/unix/unixd.h	(working copy)
@@ -129,11 +129,17 @@ typedef struct {
      * eg. idle_spawn_rate).
      */
     int num_buckets, max_buckets;
+
+    /* Hooked mpm_query function. */
+    int (*mpm_query_fn)(int, int*, apr_status_t*);
 } ap_unixd_mpm_retained_data;
 
 AP_DECLARE(ap_unixd_mpm_retained_data *) ap_unixd_mpm_get_retained_data(void);
 AP_DECLARE(void) ap_unixd_mpm_set_signals(apr_pool_t *pconf, int once_process);
 
+AP_DECLARE(void) ap_unixd_hook_mpm_query(apr_pool_t *pconf,
+                                         int (*fn)(int, int *, apr_status_t*));
+
 #ifdef __cplusplus
 }
 #endif
--- server/mpm/event/event.c	(revision 1809833)
+++ server/mpm/event/event.c	(working copy)
@@ -3597,7 +3597,7 @@ static void event_hooks(apr_pool_t * p)
     ap_hook_post_config(event_post_config, NULL, NULL, APR_HOOK_MIDDLE);
     ap_hook_check_config(event_check_config, NULL, NULL, APR_HOOK_MIDDLE);
     ap_hook_mpm(event_run, NULL, NULL, APR_HOOK_MIDDLE);
-    ap_hook_mpm_query(event_query, NULL, NULL, APR_HOOK_MIDDLE);
+    ap_unixd_hook_mpm_query(p, event_query);
     ap_hook_mpm_register_timed_callback(event_register_timed_callback, NULL, NULL,
                                         APR_HOOK_MIDDLE);
     ap_hook_pre_read_request(event_pre_read_request, NULL, NULL, APR_HOOK_MIDDLE);
--- server/mpm/prefork/prefork.c	(revision 1809833)
+++ server/mpm/prefork/prefork.c	(working copy)
@@ -1423,7 +1423,7 @@ static void prefork_hooks(apr_pool_t *p)
     ap_hook_pre_config(prefork_pre_config, NULL, NULL, APR_HOOK_REALLY_FIRST);
     ap_hook_check_config(prefork_check_config, NULL, NULL, APR_HOOK_MIDDLE);
     ap_hook_mpm(prefork_run, NULL, NULL, APR_HOOK_MIDDLE);
-    ap_hook_mpm_query(prefork_query, NULL, NULL, APR_HOOK_MIDDLE);
+    ap_unixd_hook_mpm_query(p, prefork_query);
     ap_hook_mpm_get_name(prefork_get_name, NULL, NULL, APR_HOOK_MIDDLE);
 }
 
--- server/mpm/worker/worker.c	(revision 1809833)
+++ server/mpm/worker/worker.c	(working copy)
@@ -2257,7 +2257,7 @@ static void worker_hooks(apr_pool_t *p)
     ap_hook_pre_config(worker_pre_config, NULL, NULL, APR_HOOK_REALLY_FIRST);
     ap_hook_check_config(worker_check_config, NULL, NULL, APR_HOOK_MIDDLE);
     ap_hook_mpm(worker_run, NULL, NULL, APR_HOOK_MIDDLE);
-    ap_hook_mpm_query(worker_query, NULL, NULL, APR_HOOK_MIDDLE);
+    ap_unixd_hook_mpm_query(p, worker_query);
     ap_hook_mpm_get_name(worker_get_name, NULL, NULL, APR_HOOK_MIDDLE);
 }