selftests: vDSO: simplify getrandom thread local storage and structs

Rather than using pthread_get/set_specific, just use gcc's __thread
annotation, which is noticeably faster and makes the code more obvious.

Also, just have one simplified struct called vgrnd, instead of trying to
split things up semantically. Those divisions were useful when this code
was split across several commit *messages*, but doesn't make as much
sense within a single file. This should make the code more clear and
provide a better example for implementers.
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

tools/testing/selftests/vDSO/vdso_test_getrandom.c

@@ -38,50 +38,43 @@ static struct {
 	pthread_mutex_t lock;
 	void **states;
 	size_t len, cap;
-} grnd_allocator = {
-	.lock = PTHREAD_MUTEX_INITIALIZER
-};
-
-static struct {
 	ssize_t(*fn)(void *, size_t, unsigned long, void *, size_t);
-	pthread_key_t key;
-	pthread_once_t initialized;
 	struct vgetrandom_opaque_params params;
-} grnd_ctx = {
-	.initialized = PTHREAD_ONCE_INIT
+} vgrnd = {
+	.lock = PTHREAD_MUTEX_INITIALIZER
 };
 
 static void *vgetrandom_get_state(void)
 {
 	void *state = NULL;
 
-	pthread_mutex_lock(&grnd_allocator.lock);
-	if (!grnd_allocator.len) {
+	pthread_mutex_lock(&vgrnd.lock);
+	if (!vgrnd.len) {
 		size_t page_size = getpagesize();
 		size_t new_cap;
 		size_t alloc_size, num = sysconf(_SC_NPROCESSORS_ONLN); /* Just a decent heuristic. */
 		void *new_block, *new_states;
 
-		alloc_size = (num * grnd_ctx.params.size_of_opaque_state + page_size - 1) & (~(page_size - 1));
-		num = (page_size / grnd_ctx.params.size_of_opaque_state) * (alloc_size / page_size);
-		new_block = mmap(0, alloc_size, grnd_ctx.params.mmap_prot, grnd_ctx.params.mmap_flags, -1, 0);
+		alloc_size = (num * vgrnd.params.size_of_opaque_state + page_size - 1) & (~(page_size - 1));
+		num = (page_size / vgrnd.params.size_of_opaque_state) * (alloc_size / page_size);
+		new_block = mmap(0, alloc_size, vgrnd.params.mmap_prot, vgrnd.params.mmap_flags, -1, 0);
 		if (new_block == MAP_FAILED)
 			goto out;
 
-		new_cap = grnd_allocator.cap + num;
-		new_states = reallocarray(grnd_allocator.states, new_cap, sizeof(*grnd_allocator.states));
+		new_cap = vgrnd.cap + num;
+		new_states = reallocarray(vgrnd.states, new_cap, sizeof(*vgrnd.states));
 		if (!new_states)
 			goto unmap;
-		grnd_allocator.cap = new_cap;
-		grnd_allocator.states = new_states;
+		vgrnd.cap = new_cap;
+		vgrnd.states = new_states;
 
 		for (size_t i = 0; i < num; ++i) {
-			if (((uintptr_t)new_block & (page_size - 1)) + grnd_ctx.params.size_of_opaque_state > page_size)
+			if (((uintptr_t)new_block & (page_size - 1)) + vgrnd.params.size_of_opaque_state > page_size)
 				new_block = (void *)(((uintptr_t)new_block + page_size - 1) & (~(page_size - 1)));
-			grnd_allocator.states[i] = new_block;
-			new_block += grnd_ctx.params.size_of_opaque_state;
+			vgrnd.states[i] = new_block;
+			new_block += vgrnd.params.size_of_opaque_state;
 		}
-		grnd_allocator.len = num;
+		vgrnd.len = num;
 		goto success;
 
 	unmap:
@@ -89,10 +82,10 @@ static void *vgetrandom_get_state(void)
 		goto out;
 	}
 success:
-	state = grnd_allocator.states[--grnd_allocator.len];
+	state = vgrnd.states[--vgrnd.len];
 
 out:
-	pthread_mutex_unlock(&grnd_allocator.lock);
+	pthread_mutex_unlock(&vgrnd.lock);
 	return state;
 }
 
@@ -100,27 +93,25 @@ static void vgetrandom_put_state(void *state)
 {
 	if (!state)
 		return;
-	pthread_mutex_lock(&grnd_allocator.lock);
-	grnd_allocator.states[grnd_allocator.len++] = state;
-	pthread_mutex_unlock(&grnd_allocator.lock);
+	pthread_mutex_lock(&vgrnd.lock);
+	vgrnd.states[vgrnd.len++] = state;
+	pthread_mutex_unlock(&vgrnd.lock);
 }
 
 static void vgetrandom_init(void)
 {
-	if (pthread_key_create(&grnd_ctx.key, vgetrandom_put_state) != 0)
-		return;
 	unsigned long sysinfo_ehdr = getauxval(AT_SYSINFO_EHDR);
 	if (!sysinfo_ehdr) {
 		printf("AT_SYSINFO_EHDR is not present!\n");
 		exit(KSFT_SKIP);
 	}
 	vdso_init_from_sysinfo_ehdr(sysinfo_ehdr);
-	grnd_ctx.fn = (__typeof__(grnd_ctx.fn))vdso_sym("LINUX_2.6", "__vdso_getrandom");
-	if (!grnd_ctx.fn) {
+	vgrnd.fn = (__typeof__(vgrnd.fn))vdso_sym("LINUX_2.6", "__vdso_getrandom");
+	if (!vgrnd.fn) {
 		printf("__vdso_getrandom is missing!\n");
 		exit(KSFT_FAIL);
 	}
-	if (grnd_ctx.fn(NULL, 0, 0, &grnd_ctx.params, ~0UL) != 0) {
+	if (vgrnd.fn(NULL, 0, 0, &vgrnd.params, ~0UL) != 0) {
 		printf("failed to fetch vgetrandom params!\n");
 		exit(KSFT_FAIL);
 	}
@@ -128,22 +119,16 @@ static void vgetrandom_init(void)
 
 static ssize_t vgetrandom(void *buf, size_t len, unsigned long flags)
 {
-	void *state;
+	static __thread void *state;
 
-	pthread_once(&grnd_ctx.initialized, vgetrandom_init);
-	state = pthread_getspecific(grnd_ctx.key);
 	if (!state) {
 		state = vgetrandom_get_state();
-		if (pthread_setspecific(grnd_ctx.key, state) != 0) {
-			vgetrandom_put_state(state);
-			state = NULL;
-		}
 		if (!state) {
 			printf("vgetrandom_get_state failed!\n");
 			exit(KSFT_FAIL);
 		}
 	}
-	return grnd_ctx.fn(buf, len, flags, state, grnd_ctx.params.size_of_opaque_state);
+	return vgrnd.fn(buf, len, flags, state, vgrnd.params.size_of_opaque_state);
 }
 
 enum { TRIALS = 25000000, THREADS = 256 };
@@ -265,6 +250,8 @@ static void usage(const char *argv0)
 
 int main(int argc, char *argv[])
 {
+	vgetrandom_init();
+
 	if (argc == 1) {
 		kselftest();
 		return 0;