The glibc DTV (Dynamic Thread Vector) for the main thread is never released, not even through __libc_freeres. This causes it to always show up as a reachable block when used, and sometimes, when it is extended and then reduced, as a possible leak when memcheck cannot find a pointer to the start of the block.

https://bugzilla.redhat.com/show_bug.cgi?id=1796433
https://bugzilla.redhat.com/show_bug.cgi?id=1796559

Proposed new default suppressions:

diff --git a/glibc-2.X.supp.in b/glibc-2.X.supp.in
index 126e8b338..eeefa3935 100644
--- a/glibc-2.X.supp.in
+++ b/glibc-2.X.supp.in
@@ -248,3 +248,37 @@
    Memcheck:Cond
    fun:_dl_runtime_resolve_avx_slow
 }
+
+# The main thread dynamic thread vector, DTV, which contains pointers
+# to thread local variables, isn't freed.  There are a couple of call
+# patterns that can cause it to be extended.
+{
+  dtv-addr-tail
+  Memcheck:Leak
+  match-leak-kinds: possible,reachable
+  fun:malloc
+  fun:tls_get_addr_tail*
+  fun:__tls_get_addr
+}
+
+{
+  dtv-addr-resize
+  Memcheck:Leak
+  match-leak-kinds: possible,reachable
+  fun:malloc
+  fun:_dl_resize_dtv
+  fun:_dl_update_slotinfo
+  fun:update_get_addr
+  fun:__tls_get_addr
+}
+
+{
+  dtv-addr-init
+  Memcheck:Leak
+  match-leak-kinds: possible,reachable
+  fun:malloc
+  fun:allocate_dtv_entry
+  fun:allocate_and_init
+  fun:tls_get_addr_tail*
+  fun:__tls_get_addr
+}