RED-31295 - redis: avoid race between dlopen and thread creation

It seeems that since I added the creation of the jemalloc thread redis
sometimes fails to start with the following error:

Inconsistency detected by ld.so: dl-tls.c: 493: _dl_allocate_tls_init: Assertion `listp->slotinfo[cnt].gen <= GL(dl_tls_generation)' failed!

This seems to be due to a race bug in ld.so, in which TLS creation on the
thread, collide with dlopen.

Move the creation of BIO and jemalloc threads to after modules are loaded.

plus small bugfix when trying to disable the jemalloc thread at runtime

2 files changed, 17 insertions, 0 deletions

diff --git a/src/server.c b/src/server.c
index 6aeb5aa9a..280470f63 100644
--- a/src/server.c
+++ b/src/server.c
@@ -2196,6 +2196,14 @@ void initServer(void) {
     scriptingInit(1);
     slowlogInit();
     latencyMonitorInit();
+}
+
+/* Some steps in server initialization need to be done last (after modules
+ * are loaded).
+ * Specifically, creation of threads due to a race bug in ld.so, in which
+ * Thread Local Storage initialization collides with dlopen call.
+ * see: https://sourceware.org/bugzilla/show_bug.cgi?id=19329 */
+void InitServerLast() {
     bioInit();
     server.initial_memory_usage = zmalloc_used_memory();
 }
@@ -4197,6 +4205,7 @@ int main(int argc, char **argv) {
         linuxMemoryWarnings();
     #endif
         moduleLoadFromQueue();
+        InitServerLast();
         loadDataFromDisk();
         if (server.cluster_enabled) {
             if (verifyClusterConfigWithData() == C_ERR) {
@@ -4211,6 +4220,7 @@ int main(int argc, char **argv) {
         if (server.sofd > 0)
             serverLog(LL_NOTICE,"The server is now ready to accept connections at %s", server.unixsocket);
     } else {
+        InitServerLast();
         sentinelIsRunning();
     }
 
diff --git a/src/zmalloc.c b/src/zmalloc.c
index 2482f512b..dd655620c 100644
--- a/src/zmalloc.c
+++ b/src/zmalloc.c
@@ -323,6 +323,13 @@ int zmalloc_get_allocator_info(size_t *allocated,
     je_mallctl("stats.allocated", allocated, &sz, NULL, 0);
     return 1;
 }
+
+void set_jemalloc_bg_thread(int enable) {
+    /* let jemalloc do purging asynchronously, required when there's no traffic 
+     * after flushdb */
+    char val = !!enable;
+    je_mallctl("background_thread", NULL, 0, &val, 1);
+}
 #else
 int zmalloc_get_allocator_info(size_t *allocated,
                                size_t *active,