fix segfault (watchdog thread declares threads sick and tries to restart them while they are already being restarted)

sgminer.c

@@ -7412,6 +7412,8 @@ static void *watchdog_thread(void __maybe_unused *userdata)
 
     hashmeter(-1, &zero_tv, 0);
 
+    rd_lock(&mining_thr_lock);
+
 #ifdef HAVE_CURSES
     if (curses_active_locked()) {
       struct cgpu_info *cgpu;
@@ -7547,6 +7549,7 @@ static void *watchdog_thread(void __maybe_unused *userdata)
           reinit_device(cgpu);
       }
     }
+    rd_unlock(&mining_thr_lock);
   }
 
   return NULL;
@@ -8122,6 +8125,10 @@ static void restart_mining_threads(unsigned int new_n_threads)
       thr->cgpu->drv->thread_shutdown(thr);
       thr->cgpu->shutdown = false;
     }
+  }
+
+  rd_lock(&mining_thr_lock);
+  if (mining_thr) {
     for (i = 0; i < total_devices; ++i) {
       free(devices[i]->thr);
     }
@@ -8159,14 +8166,26 @@ static void restart_mining_threads(unsigned int new_n_threads)
       thr->cgpu = cgpu;
       thr->device_thread = j;
 
+      cgtime(&thr->last);
+
+      cgpu->thr[j] = thr;
+    }
+  }
+
+  rd_unlock(&mining_thr_lock);
+
+  for (i = 0; i < total_devices; ++i) {
+    struct cgpu_info *cgpu = devices[i];
+
+    for (j = 0; j < cgpu->threads; ++j) {
+      thr = cgpu->thr[j];
+
       if (!cgpu->drv->thread_prepare(thr))
         continue;
 
       if (unlikely(thr_info_create(thr, NULL, miner_thread, thr)))
         quit(1, "thread %d create failed", thr->id);
 
-      cgpu->thr[j] = thr;
-
       /* Enable threads for devices set not to mine but disable
        * their queue in case we wish to enable them later */
       if (cgpu->deven != DEV_DISABLED) {