Fix a race in extent_grow_retained().

Set extent as active prior to registration so that other threads can't
modify it in the absence of locking.

This regression was introduced by
d27f29b468ae3e9d2b1da4a9880351d76e5a1662 (Disentangle arena and extent
locking.), via non-obvious means.  Removal of extents_mtx protection
during extent_grow_retained() execution opened up the race, but in the
presence of that locking, the code was safe.

This resolves #599.

1 files changed, 14 insertions, 9 deletions

diff --git a/src/extent.c b/src/extent.c
index 293b96e..234be54 100644
--- a/src/extent.c
+++ b/src/extent.c
@@ -453,7 +453,7 @@ extent_gdump_sub(tsdn_t *tsdn, const extent_t *extent) {
 }
 
 static bool
-extent_register(tsdn_t *tsdn, const extent_t *extent) {
+extent_register_impl(tsdn_t *tsdn, const extent_t *extent, bool gdump_add) {
 	rtree_ctx_t rtree_ctx_fallback;
 	rtree_ctx_t *rtree_ctx = tsdn_rtree_ctx(tsdn, &rtree_ctx_fallback);
 	rtree_elm_t *elm_a, *elm_b;
@@ -468,13 +468,23 @@ extent_register(tsdn_t *tsdn, const extent_t *extent) {
 	}
 	extent_rtree_release(tsdn, elm_a, elm_b);
 
-	if (config_prof) {
+	if (config_prof && gdump_add) {
 		extent_gdump_add(tsdn, extent);
 	}
 
 	return false;
 }
 
+static bool
+extent_register(tsdn_t *tsdn, const extent_t *extent) {
+	return extent_register_impl(tsdn, extent, true);
+}
+
+static bool
+extent_register_no_gdump_add(tsdn_t *tsdn, const extent_t *extent) {
+	return extent_register_impl(tsdn, extent, false);
+}
+
 static void
 extent_reregister(tsdn_t *tsdn, const extent_t *extent) {
 	bool err = extent_register(tsdn, extent);
@@ -827,17 +837,12 @@ extent_grow_retained(tsdn_t *tsdn, arena_t *arena,
 	ptr = extent_alloc_core(tsdn, arena, new_addr, alloc_size, PAGE,
 	    &zeroed, &committed, arena->dss_prec);
 	extent_init(extent, arena, ptr, alloc_size, alloc_size,
-	    arena_extent_sn_next(arena), extent_state_retained, zeroed,
+	    arena_extent_sn_next(arena), extent_state_active, zeroed,
 	    committed, false);
-	if (ptr == NULL || extent_register(tsdn, extent)) {
+	if (ptr == NULL || extent_register_no_gdump_add(tsdn, extent)) {
 		extent_dalloc(tsdn, arena, extent);
 		return NULL;
 	}
-	/*
-	 * Set the extent as active *after registration so that no gdump-related
-	 * accounting occurs during registration.
-	 */
-	extent_state_set(extent, extent_state_active);
 
 	leadsize = ALIGNMENT_CEILING((uintptr_t)ptr, PAGE_CEILING(alignment)) -
 	    (uintptr_t)ptr;