Use _Noreturn (C11) properlyHEADmaster

A function that returns with no value is a different thing from a
function that doesn't return at all.  Those are two orthogonal
concepts, commonly confused.

pthread_create(3) expects a pointer to a start routine that has a
very precise prototype:

    void *(*start_routine)(void *);

However, other thread functions, such as kernel ones, expect:

    void (*start_routine)(void *);

Providing a different one is incorrect, and has only been working
because the ABIs happen to produce a compatible function.

We should use '_Noreturn void', since it's the natural type, and
then provide a '_Noreturn void *' wrapper for pthread functions.

For consistency, replace most cases of __NORETURN or
__attribute__((noreturn)) by _Noreturn.  _Noreturn is understood
by -std=gnu89, so it should be safe to use everywhere.

Link: <https://github.com/openzfs/zfs/pull/13110#discussion_r808450136>
Link: <https://software.codidact.com/posts/285972>
Co-developed-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Signed-off-by: Alejandro Colomar <alx.manpages@gmail.com>
Cc: Brian Behlendorf <behlendorf1@llnl.gov>

31 files changed, 77 insertions, 91 deletions

diff --git a/cmd/raidz_test/raidz_test.c b/cmd/raidz_test/raidz_test.c
index a7459d8e2..8bb38f2f7 100644
--- a/cmd/raidz_test/raidz_test.c
+++ b/cmd/raidz_test/raidz_test.c
@@ -840,7 +840,7 @@ static kcondvar_t sem_cv;
 static int max_free_slots;
 static int free_slots;
 
-static void
+static _Noreturn void
 sweep_thread(void *arg)
 {
 	int err = 0;
diff --git a/cmd/zgenhostid/zgenhostid.c b/cmd/zgenhostid/zgenhostid.c
index 853931c6a..6c8f7c612 100644
--- a/cmd/zgenhostid/zgenhostid.c
+++ b/cmd/zgenhostid/zgenhostid.c
@@ -36,7 +36,7 @@
 #include <time.h>
 #include <unistd.h>
 
-static __attribute__((noreturn)) void
+static _Noreturn void
 usage(void)
 {
 	(void) fprintf(stderr,
diff --git a/cmd/zhack/zhack.c b/cmd/zhack/zhack.c
index 73ce888c0..92d20d753 100644
--- a/cmd/zhack/zhack.c
+++ b/cmd/zhack/zhack.c
@@ -57,7 +57,7 @@ static importargs_t g_importargs;
 static char *g_pool;
 static boolean_t g_readonly;
 
-static __attribute__((noreturn)) void
+static _Noreturn void
 usage(void)
 {
 	(void) fprintf(stderr,
@@ -87,7 +87,7 @@ usage(void)
 }
 
 
-static __attribute__((noreturn)) __attribute__((format(printf, 3, 4))) void
+static __attribute__((format(printf, 3, 4))) _Noreturn void
 fatal(spa_t *spa, void *tag, const char *fmt, ...)
 {
 	va_list ap;
diff --git a/cmd/ztest/ztest.c b/cmd/ztest/ztest.c
index 73ed70471..292493584 100644
--- a/cmd/ztest/ztest.c
+++ b/cmd/ztest/ztest.c
@@ -558,7 +558,7 @@ enum ztest_object {
 	ZTEST_OBJECTS
 };
 
-static void usage(boolean_t) __NORETURN;
+static _Noreturn void usage(boolean_t);
 static int ztest_scrub_impl(spa_t *spa);
 
 /*
@@ -622,7 +622,7 @@ static void sig_handler(int signo)
 
 char *fatal_msg;
 
-static __attribute__((noreturn)) __attribute__((format(printf, 2, 3))) void
+static __attribute__((format(printf, 2, 3))) _Noreturn void
 fatal(int do_perror, char *message, ...)
 {
 	va_list args;
@@ -6993,7 +6993,7 @@ ztest_resume(spa_t *spa)
 	(void) zio_resume(spa);
 }
 
-static void
+static _Noreturn void
 ztest_resume_thread(void *arg)
 {
 	spa_t *spa = arg;
@@ -7019,7 +7019,7 @@ ztest_resume_thread(void *arg)
 	thread_exit();
 }
 
-static void
+static _Noreturn void
 ztest_deadman_thread(void *arg)
 {
 	ztest_shared_t *zs = arg;
@@ -7097,7 +7097,7 @@ ztest_execute(int test, ztest_info_t *zi, uint64_t id)
 		    (double)functime / NANOSEC, zi->zi_funcname);
 }
 
-static void
+static _Noreturn void
 ztest_thread(void *arg)
 {
 	int rand;
diff --git a/config/always-compiler-options.m4 b/config/always-compiler-options.m4
index 9a0e83905..8cfd27535 100644
--- a/config/always-compiler-options.m4
+++ b/config/always-compiler-options.m4
@@ -182,32 +182,6 @@ AC_DEFUN([ZFS_AC_CONFIG_ALWAYS_CC_NO_CLOBBERED], [
 ])
 
 dnl #
-dnl # Check if cc supports -Wno-cast-function-type option.
-dnl #
-dnl # We actually invoke it with the --cast-function-type option
-dnl # and infer the 'no-' version does or doesn't exist based upon
-dnl # the results.  This is required because when checking any of
-dnl # no- prefixed options gcc always returns success.
-dnl #
-AC_DEFUN([ZFS_AC_CONFIG_ALWAYS_CC_NO_CAST_FUNCTION_TYPE], [
-	AC_MSG_CHECKING([whether $CC supports -Wno-cast-function-type])
-
-	saved_flags="$CFLAGS"
-	CFLAGS="$CFLAGS -Werror -Wcast-function-type"
-
-	AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [])], [
-		NO_CAST_FUNCTION_TYPE=-Wno-cast-function-type
-		AC_MSG_RESULT([yes])
-	], [
-		NO_CAST_FUNCTION_TYPE=
-		AC_MSG_RESULT([no])
-	])
-
-	CFLAGS="$saved_flags"
-	AC_SUBST([NO_CAST_FUNCTION_TYPE])
-])
-
-dnl #
 dnl # Check if cc supports -Wimplicit-fallthrough option.
 dnl #
 AC_DEFUN([ZFS_AC_CONFIG_ALWAYS_CC_IMPLICIT_FALLTHROUGH], [
diff --git a/config/zfs-build.m4 b/config/zfs-build.m4
index 42e57cdf7..d516f3d29 100644
--- a/config/zfs-build.m4
+++ b/config/zfs-build.m4
@@ -210,7 +210,6 @@ AC_DEFUN([ZFS_AC_CONFIG_ALWAYS], [
 	AC_SUBST(CPU_COUNT)
 
 	ZFS_AC_CONFIG_ALWAYS_CC_NO_CLOBBERED
-	ZFS_AC_CONFIG_ALWAYS_CC_NO_CAST_FUNCTION_TYPE
 	ZFS_AC_CONFIG_ALWAYS_CC_IMPLICIT_FALLTHROUGH
 	ZFS_AC_CONFIG_ALWAYS_CC_FRAME_LARGER_THAN
 	ZFS_AC_CONFIG_ALWAYS_CC_NO_FORMAT_TRUNCATION
diff --git a/include/libuutil.h b/include/libuutil.h
index cadc20d2d..043152ac2 100644
--- a/include/libuutil.h
+++ b/include/libuutil.h
@@ -85,14 +85,14 @@ extern void uu_warn(const char *, ...)
     __attribute__((format(printf, 1, 2)));
 extern void uu_vwarn(const char *, va_list)
     __attribute__((format(printf, 1, 0)));
-extern void uu_die(const char *, ...)
-    __attribute__((format(printf, 1, 2))) __NORETURN;
-extern void uu_vdie(const char *, va_list)
-    __attribute__((format(printf, 1, 0))) __NORETURN;
-extern void uu_xdie(int, const char *, ...)
-    __attribute__((format(printf, 2, 3))) __NORETURN;
-extern void uu_vxdie(int, const char *, va_list)
-    __attribute__((format(printf, 2, 0))) __NORETURN;
+extern _Noreturn void uu_die(const char *, ...)
+    __attribute__((format(printf, 1, 2)));
+extern _Noreturn void uu_vdie(const char *, va_list)
+    __attribute__((format(printf, 1, 0)));
+extern _Noreturn void uu_xdie(int, const char *, ...)
+    __attribute__((format(printf, 2, 3)));
+extern _Noreturn void uu_vxdie(int, const char *, va_list)
+    __attribute__((format(printf, 2, 0)));
 
 /*
  * Exit status functions (not to be used directly)
diff --git a/include/os/linux/spl/sys/thread.h b/include/os/linux/spl/sys/thread.h
index 6248866a9..c723b599a 100644
--- a/include/os/linux/spl/sys/thread.h
+++ b/include/os/linux/spl/sys/thread.h
@@ -62,7 +62,7 @@ typedef void (*thread_func_t)(void *);
 extern kthread_t *__thread_create(caddr_t stk, size_t  stksize,
     thread_func_t func, const char *name, void *args, size_t len, proc_t *pp,
     int state, pri_t pri);
-extern void __thread_exit(void);
+extern _Noreturn void __thread_exit(void);
 extern struct task_struct *spl_kthread_create(int (*func)(void *),
     void *data, const char namefmt[], ...);
 
diff --git a/include/sys/zfs_context.h b/include/sys/zfs_context.h
index 6d1fd83df..9d99388be 100644
--- a/include/sys/zfs_context.h
+++ b/include/sys/zfs_context.h
@@ -153,8 +153,8 @@ extern void dprintf_setup(int *argc, char **argv);
 
 extern void cmn_err(int, const char *, ...);
 extern void vcmn_err(int, const char *, va_list);
-extern void panic(const char *, ...)  __NORETURN;
-extern void vpanic(const char *, va_list)  __NORETURN;
+extern _Noreturn void panic(const char *, ...);
+extern _Noreturn void vpanic(const char *, va_list);
 
 #define	fm_panic	panic
 
diff --git a/lib/libspl/include/sys/feature_tests.h b/lib/libspl/include/sys/feature_tests.h
index be0721b50..877e0a15a 100644
--- a/lib/libspl/include/sys/feature_tests.h
+++ b/lib/libspl/include/sys/feature_tests.h
@@ -28,7 +28,6 @@
 #define	_SYS_FEATURE_TESTS_H
 
 #define	____cacheline_aligned
-#define	__NORETURN		__attribute__((__noreturn__))
 
 #if !defined(zfs_fallthrough) && !defined(_LIBCPP_VERSION)
 #if defined(HAVE_IMPLICIT_FALLTHROUGH)
diff --git a/lib/libuutil/uu_pname.c b/lib/libuutil/uu_pname.c
index 43c9e7756..b6c9f2cc0 100644
--- a/lib/libuutil/uu_pname.c
+++ b/lib/libuutil/uu_pname.c
@@ -40,8 +40,8 @@
 
 static const char *pname;
 
-static void
-uu_die_internal(int status, const char *format, va_list alist) __NORETURN;
+static _Noreturn void
+uu_die_internal(int status, const char *format, va_list alist);
 
 int uu_exit_ok_value = EXIT_SUCCESS;
 int uu_exit_fatal_value = EXIT_FAILURE;
@@ -110,7 +110,7 @@ uu_warn(const char *format, ...)
 	va_end(alist);
 }
 
-static __attribute__((format(printf, 2, 0))) __NORETURN void
+static __attribute__((format(printf, 2, 0))) _Noreturn void
 uu_die_internal(int status, const char *format, va_list alist)
 {
 	uu_warn_internal(errno, format, alist);
diff --git a/lib/libzpool/Makefile.am b/lib/libzpool/Makefile.am
index 60ffbb7ee..e60a906a5 100644
--- a/lib/libzpool/Makefile.am
+++ b/lib/libzpool/Makefile.am
@@ -24,11 +24,6 @@ AM_CFLAGS += $(ZLIB_CFLAGS)
 
 AM_CFLAGS += -DLIB_ZPOOL_BUILD
 
-# For the void (*)(void *) -> void *(*)(void *) cast in zk_thread_create()
-# See https://github.com/openzfs/zfs/pull/13110#discussion_r808450136
-kernel.$(OBJEXT): CFLAGS += $(NO_CAST_FUNCTION_TYPE)
-kernel.l$(OBJEXT): CFLAGS += $(NO_CAST_FUNCTION_TYPE)
-
 lib_LTLIBRARIES = libzpool.la
 
 USER_C = \
diff --git a/lib/libzpool/kernel.c b/lib/libzpool/kernel.c
index 8a588e5a9..6b29d6d39 100644
--- a/lib/libzpool/kernel.c
+++ b/lib/libzpool/kernel.c
@@ -75,12 +75,28 @@ struct proc p0;
 #define	TS_STACK_MIN	MAX(PTHREAD_STACK_MIN, 32768)
 #define	TS_STACK_MAX	(256 * 1024)
 
+struct zk_thread_wrapper {
+	void (*func)(void *);
+	void *arg;
+};
+
+static void *
+zk_thread_wrapper(void *arg)
+{
+	struct zk_thread_wrapper ztw;
+	memcpy(&ztw, arg, sizeof (ztw));
+	free(arg);
+	ztw.func(ztw.arg);
+	return (NULL);
+}
+
 kthread_t *
 zk_thread_create(void (*func)(void *), void *arg, size_t stksize, int state)
 {
 	pthread_attr_t attr;
 	pthread_t tid;
 	char *stkstr;
+	struct zk_thread_wrapper *ztw;
 	int detachstate = PTHREAD_CREATE_DETACHED;
 
 	VERIFY0(pthread_attr_init(&attr));
@@ -117,7 +133,10 @@ zk_thread_create(void (*func)(void *), void *arg, size_t stksize, int state)
 	VERIFY0(pthread_attr_setstacksize(&attr, stksize));
 	VERIFY0(pthread_attr_setguardsize(&attr, PAGESIZE));
 
-	VERIFY0(pthread_create(&tid, &attr, (void *(*)(void *))func, arg));
+	VERIFY(ztw = malloc(sizeof (*ztw)));
+	ztw->func = func;
+	ztw->arg = arg;
+	VERIFY0(pthread_create(&tid, &attr, zk_thread_wrapper, ztw));
 	VERIFY0(pthread_attr_destroy(&attr));
 
 	return ((void *)(uintptr_t)tid);
diff --git a/lib/libzpool/taskq.c b/lib/libzpool/taskq.c
index 8a6113091..146044bb8 100644
--- a/lib/libzpool/taskq.c
+++ b/lib/libzpool/taskq.c
@@ -211,7 +211,7 @@ taskq_wait_outstanding(taskq_t *tq, taskqid_t id)
 	taskq_wait(tq);
 }
 
-static void
+static _Noreturn void
 taskq_thread(void *arg)
 {
 	taskq_t *tq = arg;
diff --git a/module/lua/ldo.c b/module/lua/ldo.c
index 01e5d6fd3..2ee9f665d 100644
--- a/module/lua/ldo.c
+++ b/module/lua/ldo.c
@@ -91,7 +91,7 @@ static intptr_t stack_remaining(void) {
 typedef	struct _label_t { long long unsigned val[JMP_BUF_CNT]; } label_t;
 
 int setjmp(label_t *) __attribute__ ((__nothrow__));
-extern void longjmp(label_t *) __attribute__((__noreturn__));
+extern _Noreturn void longjmp(label_t *);
 
 #define LUAI_THROW(L,c)		longjmp(&(c)->b)
 #define LUAI_TRY(L,c,a)		if (setjmp(&(c)->b) == 0) { a }
diff --git a/module/os/linux/spl/spl-thread.c b/module/os/linux/spl/spl-thread.c
index 16d2ca1b1..ed766f1cf 100644
--- a/module/os/linux/spl/spl-thread.c
+++ b/module/os/linux/spl/spl-thread.c
@@ -62,7 +62,7 @@ thread_generic_wrapper(void *arg)
 	return (0);
 }
 
-void
+_Noreturn void
 __thread_exit(void)
 {
 	tsd_exit();
diff --git a/module/zfs/arc.c b/module/zfs/arc.c
index 7ca37c176..744df2423 100644
--- a/module/zfs/arc.c
+++ b/module/zfs/arc.c
@@ -928,7 +928,7 @@ static unsigned long l2arc_rebuild_blocks_min_l2size = 1024 * 1024 * 1024;
 
 /* L2ARC persistence rebuild control routines. */
 void l2arc_rebuild_vdev(vdev_t *vd, boolean_t reopen);
-static void l2arc_dev_rebuild_thread(void *arg);
+static _Noreturn void l2arc_dev_rebuild_thread(void *arg);
 static int l2arc_rebuild(l2arc_dev_t *dev);
 
 /* L2ARC persistence read I/O routines. */
@@ -9706,7 +9706,7 @@ l2arc_hdr_limit_reached(void)
  * This thread feeds the L2ARC at regular intervals.  This is the beating
  * heart of the L2ARC.
  */
-static void
+static _Noreturn void
 l2arc_feed_thread(void *unused)
 {
 	(void) unused;
@@ -10145,7 +10145,7 @@ l2arc_spa_rebuild_start(spa_t *spa)
 /*
  * Main entry point for L2ARC rebuilding.
  */
-static void
+static _Noreturn void
 l2arc_dev_rebuild_thread(void *arg)
 {
 	l2arc_dev_t *dev = arg;
diff --git a/module/zfs/dbuf.c b/module/zfs/dbuf.c
index 26f0d72b2..cb2b7e5a1 100644
--- a/module/zfs/dbuf.c
+++ b/module/zfs/dbuf.c
@@ -778,7 +778,7 @@ dbuf_evict_one(void)
  * of the dbuf cache is at or below the maximum size. Once the dbuf is aged
  * out of the cache it is destroyed and becomes eligible for arc eviction.
  */
-static void
+static _Noreturn void
 dbuf_evict_thread(void *unused)
 {
 	(void) unused;
diff --git a/module/zfs/dmu_recv.c b/module/zfs/dmu_recv.c
index b507d37c7..b34c1bc69 100644
--- a/module/zfs/dmu_recv.c
+++ b/module/zfs/dmu_recv.c
@@ -2802,7 +2802,7 @@ receive_process_record(struct receive_writer_arg *rwa,
  * dmu_recv_stream's worker thread; pull records off the queue, and then call
  * receive_process_record  When we're done, signal the main thread and exit.
  */
-static void
+static _Noreturn void
 receive_writer_thread(void *arg)
 {
 	struct receive_writer_arg *rwa = arg;
diff --git a/module/zfs/dmu_redact.c b/module/zfs/dmu_redact.c
index 46f498289..ab2b5f23e 100644
--- a/module/zfs/dmu_redact.c
+++ b/module/zfs/dmu_redact.c
@@ -351,7 +351,7 @@ redact_cb(spa_t *spa, zilog_t *zilog, const blkptr_t *bp,
 	return (0);
 }
 
-static void
+static _Noreturn void
 redact_traverse_thread(void *arg)
 {
 	struct redact_thread_arg *rt_arg = arg;
@@ -837,7 +837,7 @@ struct redact_merge_thread_arg {
 	int error_code;
 };
 
-static void
+static _Noreturn void
 redact_merge_thread(void *arg)
 {
 	struct redact_merge_thread_arg *rmta = arg;
diff --git a/module/zfs/dmu_send.c b/module/zfs/dmu_send.c
index b388a3c11..021dffefa 100644
--- a/module/zfs/dmu_send.c
+++ b/module/zfs/dmu_send.c
@@ -1234,7 +1234,7 @@ redact_list_cb(redact_block_phys_t *rb, void *arg)
  * error code of the thread in case something goes wrong, and pushes the End of
  * Stream record when the traverse_dataset call has finished.
  */
-static void
+static _Noreturn void
 send_traverse_thread(void *arg)
 {
 	struct send_thread_arg *st_arg = arg;
@@ -1324,7 +1324,7 @@ get_next_range(bqueue_t *bq, struct send_range *prev)
 	return (next);
 }
 
-static void
+static _Noreturn void
 redact_list_thread(void *arg)
 {
 	struct redact_list_thread_arg *rlt_arg = arg;
@@ -1519,7 +1519,7 @@ find_next_range(struct send_range **ranges, bqueue_t **qs, uint64_t *out_mask)
  * data from the redact_list_thread and use that to determine which blocks
  * should be redacted.
  */
-static void
+static _Noreturn void
 send_merge_thread(void *arg)
 {
 	struct send_merge_thread_arg *smt_arg = arg;
@@ -1744,7 +1744,7 @@ enqueue_range(struct send_reader_thread_arg *srta, bqueue_t *q, dnode_t *dn,
  * some indirect blocks can be discarded because they're not holes. Second,
  * it issues prefetches for the data we need to send.
  */
-static void
+static _Noreturn void
 send_reader_thread(void *arg)
 {
 	struct send_reader_thread_arg *srta = arg;
diff --git a/module/zfs/mmp.c b/module/zfs/mmp.c
index abdce3a32..f8ba21695 100644
--- a/module/zfs/mmp.c
+++ b/module/zfs/mmp.c
@@ -187,7 +187,7 @@ uint_t zfs_multihost_import_intervals = MMP_DEFAULT_IMPORT_INTERVALS;
 uint_t zfs_multihost_fail_intervals = MMP_DEFAULT_FAIL_INTERVALS;
 
 static void *const mmp_tag = "mmp_write_uberblock";
-static void mmp_thread(void *arg);
+static _Noreturn void mmp_thread(void *arg);
 
 void
 mmp_init(spa_t *spa)
@@ -217,7 +217,7 @@ mmp_thread_enter(mmp_thread_t *mmp, callb_cpr_t *cpr)
 	mutex_enter(&mmp->mmp_thread_lock);
 }
 
-static void
+static _Noreturn void
 mmp_thread_exit(mmp_thread_t *mmp, kthread_t **mpp, callb_cpr_t *cpr)
 {
 	ASSERT(*mpp != NULL);
@@ -537,7 +537,7 @@ mmp_write_uberblock(spa_t *spa)
 	zio_nowait(zio);
 }
 
-static void
+static _Noreturn void
 mmp_thread(void *arg)
 {
 	spa_t *spa = (spa_t *)arg;
diff --git a/module/zfs/spa.c b/module/zfs/spa.c
index 881a7c94e..744bcb434 100644
--- a/module/zfs/spa.c
+++ b/module/zfs/spa.c
@@ -8139,7 +8139,7 @@ spa_async_autoexpand(spa_t *spa, vdev_t *vd)
 	spa_event_notify(vd->vdev_spa, vd, NULL, ESC_ZFS_VDEV_AUTOEXPAND);
 }
 
-static void
+static _Noreturn void
 spa_async_thread(void *arg)
 {
 	spa_t *spa = (spa_t *)arg;
diff --git a/module/zfs/txg.c b/module/zfs/txg.c
index 9655efdc4..7908183ca 100644
--- a/module/zfs/txg.c
+++ b/module/zfs/txg.c
@@ -108,8 +108,8 @@
  * now transition to the syncing state.
  */
 
-static void txg_sync_thread(void *arg);
-static void txg_quiesce_thread(void *arg);
+static _Noreturn void txg_sync_thread(void *arg);
+static _Noreturn void txg_quiesce_thread(void *arg);
 
 int zfs_txg_timeout = 5;	/* max seconds worth of delta per txg */
 
@@ -514,7 +514,7 @@ txg_has_quiesced_to_sync(dsl_pool_t *dp)
 	return (tx->tx_quiesced_txg != 0);
 }
 
-static void
+static _Noreturn void
 txg_sync_thread(void *arg)
 {
 	dsl_pool_t *dp = arg;
@@ -605,7 +605,7 @@ txg_sync_thread(void *arg)
 	}
 }
 
-static void
+static _Noreturn void
 txg_quiesce_thread(void *arg)
 {
 	dsl_pool_t *dp = arg;
diff --git a/module/zfs/vdev_initialize.c b/module/zfs/vdev_initialize.c
index ce1385d5a..6c4528e93 100644
--- a/module/zfs/vdev_initialize.c
+++ b/module/zfs/vdev_initialize.c
@@ -488,7 +488,7 @@ vdev_initialize_range_add(void *arg, uint64_t start, uint64_t size)
 	vdev_xlate_walk(vd, &logical_rs, vdev_initialize_xlate_range_add, arg);
 }
 
-static void
+static _Noreturn void
 vdev_initialize_thread(void *arg)
 {
 	vdev_t *vd = arg;
diff --git a/module/zfs/vdev_rebuild.c b/module/zfs/vdev_rebuild.c
index a6866a8b2..510463b1f 100644
--- a/module/zfs/vdev_rebuild.c
+++ b/module/zfs/vdev_rebuild.c
@@ -133,7 +133,7 @@ static int zfs_rebuild_scrub_enabled = 1;
 /*
  * For vdev_rebuild_initiate_sync() and vdev_rebuild_reset_sync().
  */
-static void vdev_rebuild_thread(void *arg);
+static _Noreturn void vdev_rebuild_thread(void *arg);
 
 /*
  * Clear the per-vdev rebuild bytes value for a vdev tree.
@@ -736,7 +736,7 @@ vdev_rebuild_load(vdev_t *vd)
  * Each scan thread is responsible for rebuilding a top-level vdev.  The
  * rebuild progress in tracked on-disk in VDEV_TOP_ZAP_VDEV_REBUILD_PHYS.
  */
-static void
+static _Noreturn void
 vdev_rebuild_thread(void *arg)
 {
 	vdev_t *vd = arg;
diff --git a/module/zfs/vdev_removal.c b/module/zfs/vdev_removal.c
index 64be84edd..6887b2f52 100644
--- a/module/zfs/vdev_removal.c
+++ b/module/zfs/vdev_removal.c
@@ -140,7 +140,7 @@ int zfs_removal_suspend_progress = 0;
 
 #define	VDEV_REMOVAL_ZAP_OBJS	"lzap"
 
-static void spa_vdev_remove_thread(void *arg);
+static _Noreturn void spa_vdev_remove_thread(void *arg);
 static int spa_vdev_remove_cancel_impl(spa_t *spa);
 
 static void
@@ -1589,7 +1589,7 @@ spa_remove_max_segment(spa_t *spa)
  * TXG have completed (see spa_txg_zio) and writes the new mappings to disk
  * (see vdev_mapping_sync()).
  */
-static void
+static _Noreturn void
 spa_vdev_remove_thread(void *arg)
 {
 	spa_t *spa = arg;
diff --git a/module/zfs/vdev_trim.c b/module/zfs/vdev_trim.c
index 39aee3786..77f27406e 100644
--- a/module/zfs/vdev_trim.c
+++ b/module/zfs/vdev_trim.c
@@ -834,7 +834,7 @@ vdev_trim_range_add(void *arg, uint64_t start, uint64_t size)
  * by its ms_allocatable.  While a metaslab is undergoing trimming it is
  * not eligible for new allocations.
  */
-static void
+static _Noreturn void
 vdev_trim_thread(void *arg)
 {
 	vdev_t *vd = arg;
@@ -1175,7 +1175,7 @@ vdev_trim_range_verify(void *arg, uint64_t start, uint64_t size)
  * N.B. This behavior is different from a manual TRIM where a thread
  * is created for each leaf vdev, instead of each top-level vdev.
  */
-static void
+static _Noreturn void
 vdev_autotrim_thread(void *arg)
 {
 	vdev_t *vd = arg;
@@ -1514,7 +1514,7 @@ vdev_autotrim_restart(spa_t *spa)
 		vdev_autotrim(spa);
 }
 
-static void
+static _Noreturn void
 vdev_trim_l2arc_thread(void *arg)
 {
 	vdev_t		*vd = arg;
diff --git a/module/zfs/zthr.c b/module/zfs/zthr.c
index 52ddffae7..2cb600a71 100644
--- a/module/zfs/zthr.c
+++ b/module/zfs/zthr.c
@@ -231,7 +231,7 @@ struct zthr {
 	const char	*zthr_name;
 };
 
-static void
+static _Noreturn void
 zthr_procedure(void *arg)
 {
 	zthr_t *t = arg;
diff --git a/tests/zfs-tests/cmd/mkbusy/mkbusy.c b/tests/zfs-tests/cmd/mkbusy/mkbusy.c
index 50a4f90a2..c32f1ecdc 100644
--- a/tests/zfs-tests/cmd/mkbusy/mkbusy.c
+++ b/tests/zfs-tests/cmd/mkbusy/mkbusy.c
@@ -31,14 +31,14 @@
 #include <string.h>
 
 
-static __attribute__((noreturn)) void
+static _Noreturn void
 usage(char *progname)
 {
 	(void) fprintf(stderr, "Usage: %s <dirname|filename>\n", progname);
 	exit(1);
 }
 
-static __attribute__((noreturn)) void
+static _Noreturn void
 fail(char *err)
 {
 	perror(err);
diff --git a/tests/zfs-tests/cmd/mkfile/mkfile.c b/tests/zfs-tests/cmd/mkfile/mkfile.c
index 673cbf9e0..f59a01efa 100644
--- a/tests/zfs-tests/cmd/mkfile/mkfile.c
+++ b/tests/zfs-tests/cmd/mkfile/mkfile.c
@@ -44,7 +44,7 @@
 
 #define	FILE_MODE	(S_ISVTX + S_IRUSR + S_IWUSR)
 
-static void usage(void) __attribute__((noreturn));
+static _Noreturn void usage(void);
 
 int
 main(int argc, char **argv)