Allow setting extent hooks on uninitialized auto arenas.

Setting extent hooks can result in initializing an unused auto arena.  This is
useful to install extent hooks on auto arenas from the beginning.

Author: interwq

src/ctl.c

@@ -2251,20 +2251,41 @@ arena_i_extent_hooks_ctl(tsd_t *tsd, const size_t *mib, size_t miblen,
 
 	malloc_mutex_lock(tsd_tsdn(tsd), &ctl_mtx);
 	MIB_UNSIGNED(arena_ind, 1);
-	if (arena_ind < narenas_total_get() && (arena =
-	    arena_get(tsd_tsdn(tsd), arena_ind, false)) != NULL) {
-		if (newp != NULL) {
-			extent_hooks_t *old_extent_hooks;
-			extent_hooks_t *new_extent_hooks
-			    JEMALLOC_CC_SILENCE_INIT(NULL);
-			WRITE(new_extent_hooks, extent_hooks_t *);
-			old_extent_hooks = extent_hooks_set(tsd, arena,
-			    new_extent_hooks);
+	if (arena_ind < narenas_total_get()) {
+		extent_hooks_t *old_extent_hooks;
+		arena = arena_get(tsd_tsdn(tsd), arena_ind, false);
+		if (arena == NULL) {
+			if (arena_ind >= narenas_auto) {
+				ret = EFAULT;
+				goto label_return;
+			}
+			old_extent_hooks =
+			    (extent_hooks_t *)&extent_hooks_default;
 			READ(old_extent_hooks, extent_hooks_t *);
+			if (newp != NULL) {
+				/* Initialize a new arena as a side effect. */
+				extent_hooks_t *new_extent_hooks
+				    JEMALLOC_CC_SILENCE_INIT(NULL);
+				WRITE(new_extent_hooks, extent_hooks_t *);
+				arena = arena_init(tsd_tsdn(tsd), arena_ind,
+				    new_extent_hooks);
+				if (arena == NULL) {
+					ret = EFAULT;
+					goto label_return;
+				}
+			}
 		} else {
-			extent_hooks_t *old_extent_hooks =
-			    extent_hooks_get(arena);
-			READ(old_extent_hooks, extent_hooks_t *);
+			if (newp != NULL) {
+				extent_hooks_t *new_extent_hooks
+				    JEMALLOC_CC_SILENCE_INIT(NULL);
+				WRITE(new_extent_hooks, extent_hooks_t *);
+				old_extent_hooks = extent_hooks_set(tsd, arena,
+				    new_extent_hooks);
+				READ(old_extent_hooks, extent_hooks_t *);
+			} else {
+				old_extent_hooks = extent_hooks_get(arena);
+				READ(old_extent_hooks, extent_hooks_t *);
+			}
 		}
 	} else {
 		ret = EFAULT;

test/integration/extent.c

@@ -98,6 +98,43 @@ test_extent_body(unsigned arena_ind) {
 	dallocx(p, flags);
 }
 
+static void
+test_manual_hook_auto_arena(void) {
+	unsigned narenas;
+	size_t old_size, new_size, sz;
+	size_t hooks_mib[3];
+	size_t hooks_miblen;
+	extent_hooks_t *new_hooks, *old_hooks;
+
+	extent_hooks_prep();
+
+	sz = sizeof(unsigned);
+	/* Get number of auto arenas. */
+	assert_d_eq(mallctl("opt.narenas", (void *)&narenas, &sz, NULL, 0),
+	    0, "Unexpected mallctl() failure");
+	if (narenas == 1) {
+		return;
+	}
+
+	/* Install custom extent hooks on arena 1 (might not be initialized). */
+	hooks_miblen = sizeof(hooks_mib)/sizeof(size_t);
+	assert_d_eq(mallctlnametomib("arena.0.extent_hooks", hooks_mib,
+	    &hooks_miblen), 0, "Unexpected mallctlnametomib() failure");
+	hooks_mib[1] = 1;
+	old_size = sizeof(extent_hooks_t *);
+	new_hooks = &hooks;
+	new_size = sizeof(extent_hooks_t *);
+	assert_d_eq(mallctlbymib(hooks_mib, hooks_miblen, (void *)&old_hooks,
+	    &old_size, (void *)&new_hooks, new_size), 0,
+	    "Unexpected extent_hooks error");
+	static bool auto_arena_created = false;
+	if (old_hooks != &hooks) {
+		assert_b_eq(auto_arena_created, false,
+		    "Expected auto arena 1 created only once.");
+		auto_arena_created = true;
+	}
+}
+
 static void
 test_manual_hook_body(void) {
 	unsigned arena_ind;
@@ -169,6 +206,7 @@ test_manual_hook_body(void) {
 }
 
 TEST_BEGIN(test_extent_manual_hook) {
+	test_manual_hook_auto_arena();
 	test_manual_hook_body();
 
 	/* Test failure paths. */