mimic: mds: disallow dumping huge caches to formatter

src/common/options.cc

@@ -7093,6 +7093,16 @@ std::vector<Option> get_mds_options() {
     Option("mds_max_retries_on_remount_failure", Option::TYPE_UINT, Option::LEVEL_ADVANCED)
      .set_default(5)
      .set_description("number of consecutive failed remount attempts for invalidating kernel dcache after which client would abort."),
+
+    Option("mds_dump_cache_threshold_formatter", Option::TYPE_SIZE, Option::LEVEL_DEV)
+     .set_default(1_G)
+     .set_description("threshold for cache usage to disallow \"dump cache\" operation to formatter")
+     .set_long_description("Disallow MDS from dumping caches to formatter via \"dump cache\" command if cache usage exceeds this threshold."),
+
+    Option("mds_dump_cache_threshold_file", Option::TYPE_SIZE, Option::LEVEL_DEV)
+     .set_default(0)
+     .set_description("threshold for cache usage to disallow \"dump cache\" operation to file")
+     .set_long_description("Disallow MDS from dumping caches to file via \"dump cache\" command if cache usage exceeds this threshold."),
   });
 }
 

src/mds/MDCache.cc

@@ -12292,6 +12292,32 @@ int MDCache::dump_cache(Formatter *f)
 int MDCache::dump_cache(std::string_view fn, Formatter *f)
 {
   int r = 0;
+
+  // dumping large caches may cause mds to hang or worse get killed.
+  // so, disallow the dump if the cache size exceeds the configured
+  // threshold, which is 1G for formatter and unlimited for file (note
+  // that this can be jacked up by the admin... and is nothing but foot
+  // shooting, but the option itself is for devs and hence dangerous to
+  // tune). TODO: remove this when fixed.
+  uint64_t threshold = f ?
+    g_conf->get_val<Option::size_t>("mds_dump_cache_threshold_formatter") :
+    g_conf->get_val<Option::size_t>("mds_dump_cache_threshold_file");
+
+  if (threshold && cache_size() > threshold) {
+    if (f) {
+      std::stringstream ss;
+      ss << "cache usage exceeds dump threshold";
+      f->open_object_section("result");
+      f->dump_string("error", ss.str());
+      f->close_section();
+    } else {
+      derr << "cache usage exceeds dump threshold" << dendl;
+      r = -EINVAL;
+    }
+    return r;
+  }
+
+  r = 0;
   int fd = -1;
 
   if (f) {

src/mds/MDSDaemon.cc

@@ -383,6 +383,8 @@ const char** MDSDaemon::get_tracked_conf_keys() const
     "mds_cache_reservation",
     "mds_health_cache_threshold",
     "mds_cache_mid",
+    "mds_dump_cache_threshold_formatter",
+    "mds_dump_cache_threshold_file",
     // MDBalancer
     "mds_bal_fragment_dirs",
     "mds_bal_fragment_interval",