From 54ef51121b1d7d3c3be9807a88827fb98ba48b67 Mon Sep 17 00:00:00 2001
From: Slobodan Predolac <spredolac@fb.com>
Date: Fri, 8 May 2026 10:01:00 -0700
Subject: [PATCH] Extract postfork-child tcache list relink into
 tcache_arena_postfork_child

---
 include/jemalloc/internal/tcache_externs.h |  1 +
 src/arena.c                                | 16 +--------
 src/tcache.c                               | 39 +++++++++++++++++-----
 3 files changed, 32 insertions(+), 24 deletions(-)

diff --git a/include/jemalloc/internal/tcache_externs.h b/include/jemalloc/internal/tcache_externs.h
index b7fdb5a4..97024b2b 100644
--- a/include/jemalloc/internal/tcache_externs.h
+++ b/include/jemalloc/internal/tcache_externs.h
@@ -73,6 +73,7 @@ void      tcaches_destroy(tsd_t *tsd, unsigned ind);
 bool      tcache_boot(tsdn_t *tsdn, base_t *base);
 void      tcache_arena_associate(
          tsdn_t *tsdn, tcache_slow_t *tcache_slow, tcache_t *tcache, arena_t *arena);
+void      tcache_arena_postfork_child(tsdn_t *tsdn, arena_t *arena);
 void tcache_prefork(tsdn_t *tsdn);
 void tcache_postfork_parent(tsdn_t *tsdn);
 void tcache_postfork_child(tsdn_t *tsdn);
diff --git a/src/arena.c b/src/arena.c
index 516791c8..a76b26e8 100644
--- a/src/arena.c
+++ b/src/arena.c
@@ -2089,21 +2089,7 @@ arena_postfork_child(tsdn_t *tsdn, arena_t *arena) {
 	if (tsd_iarena_get(tsdn_tsd(tsdn)) == arena) {
 		arena_nthreads_inc(arena, true);
 	}
-	if (config_stats) {
-		ql_new(&arena->tcache_ql);
-		ql_new(&arena->cache_bin_array_descriptor_ql);
-		tcache_slow_t *tcache_slow = tcache_slow_get(tsdn_tsd(tsdn));
-		if (tcache_slow != NULL && tcache_slow->arena == arena) {
-			tcache_t *tcache = tcache_slow->tcache;
-			ql_elm_new(tcache_slow, link);
-			ql_tail_insert(&arena->tcache_ql, tcache_slow, link);
-			cache_bin_array_descriptor_init(
-			    &tcache_slow->cache_bin_array_descriptor,
-			    tcache->bins);
-			ql_tail_insert(&arena->cache_bin_array_descriptor_ql,
-			    &tcache_slow->cache_bin_array_descriptor, link);
-		}
-	}
+	tcache_arena_postfork_child(tsdn, arena);
 
 	for (unsigned i = 0; i < nbins_total; i++) {
 		JEMALLOC_SUPPRESS_WARN_ON_USAGE(
diff --git a/src/tcache.c b/src/tcache.c
index d898e0d5..c843dee7 100644
--- a/src/tcache.c
+++ b/src/tcache.c
@@ -720,6 +720,22 @@ tcache_bin_ncached_max_read(
 	return false;
 }
 
+/*
+ * Insert tcache_slow into arena's tcache list.  Caller must hold
+ * arena->tcache_ql_mtx, OR be in the postfork-child path (single-threaded,
+ * mutex re-init pending).  config_stats must be true.
+ */
+static void
+tcache_arena_link(arena_t *arena, tcache_slow_t *tcache_slow,
+    tcache_t *tcache) {
+	ql_elm_new(tcache_slow, link);
+	ql_tail_insert(&arena->tcache_ql, tcache_slow, link);
+	cache_bin_array_descriptor_init(
+	    &tcache_slow->cache_bin_array_descriptor, tcache->bins);
+	ql_tail_insert(&arena->cache_bin_array_descriptor_ql,
+	    &tcache_slow->cache_bin_array_descriptor, link);
+}
+
 void
 tcache_arena_associate(tsdn_t *tsdn, tcache_slow_t *tcache_slow,
     tcache_t *tcache, arena_t *arena) {
@@ -727,16 +743,8 @@ tcache_arena_associate(tsdn_t *tsdn, tcache_slow_t *tcache_slow,
 	tcache_slow->arena = arena;
 
 	if (config_stats) {
-		/* Link into list of extant tcaches. */
 		malloc_mutex_lock(tsdn, &arena->tcache_ql_mtx);
-
-		ql_elm_new(tcache_slow, link);
-		ql_tail_insert(&arena->tcache_ql, tcache_slow, link);
-		cache_bin_array_descriptor_init(
-		    &tcache_slow->cache_bin_array_descriptor, tcache->bins);
-		ql_tail_insert(&arena->cache_bin_array_descriptor_ql,
-		    &tcache_slow->cache_bin_array_descriptor, link);
-
+		tcache_arena_link(arena, tcache_slow, tcache);
 		malloc_mutex_unlock(tsdn, &arena->tcache_ql_mtx);
 	}
 }
@@ -776,6 +784,19 @@ tcache_arena_reassociate(tsdn_t *tsdn, tcache_slow_t *tcache_slow,
 	tcache_arena_associate(tsdn, tcache_slow, tcache, arena);
 }
 
+void
+tcache_arena_postfork_child(tsdn_t *tsdn, arena_t *arena) {
+	if (!config_stats) {
+		return;
+	}
+	ql_new(&arena->tcache_ql);
+	ql_new(&arena->cache_bin_array_descriptor_ql);
+	tcache_slow_t *tcache_slow = tcache_slow_get(tsdn_tsd(tsdn));
+	if (tcache_slow != NULL && tcache_slow->arena == arena) {
+		tcache_arena_link(arena, tcache_slow, tcache_slow->tcache);
+	}
+}
+
 static void
 tcache_default_settings_init(tcache_slow_t *tcache_slow) {
 	assert(tcache_slow != NULL);