Index: head/sys/kern/vfs_aio.c
===================================================================
--- head/sys/kern/vfs_aio.c
+++ head/sys/kern/vfs_aio.c
@@ -311,6 +311,7 @@
 static int	aio_qphysio(struct proc *p, struct kaiocb *job);
 static void	aio_daemon(void *param);
 static void	aio_bio_done_notify(struct proc *userp, struct kaiocb *job);
+static bool	aio_clear_cancel_function_locked(struct kaiocb *job);
 static int	aio_kick(struct proc *userp);
 static void	aio_kick_nowait(struct proc *userp);
 static void	aio_kick_helper(void *context, int pending);
@@ -919,7 +920,7 @@
 			if (--sjob->pending > 0)
 				continue;
 			TAILQ_REMOVE(&ki->kaio_syncqueue, sjob, list);
-			if (!aio_clear_cancel_function(sjob))
+			if (!aio_clear_cancel_function_locked(sjob))
 				continue;
 			TAILQ_INSERT_TAIL(&ki->kaio_syncready, sjob, list);
 			schedule_fsync = true;
@@ -967,40 +968,57 @@
 	return ((job->jobflags & KAIOCB_CLEARED) != 0);
 }
 
-bool
-aio_clear_cancel_function(struct kaiocb *job)
+static bool
+aio_clear_cancel_function_locked(struct kaiocb *job)
 {
-	struct kaioinfo *ki;
 
-	ki = job->userproc->p_aioinfo;
-	AIO_LOCK(ki);
+	AIO_LOCK_ASSERT(job->userproc->p_aioinfo, MA_OWNED);
 	MPASS(job->cancel_fn != NULL);
 	if (job->jobflags & KAIOCB_CANCELLING) {
 		job->jobflags |= KAIOCB_CLEARED;
-		AIO_UNLOCK(ki);
 		return (false);
 	}
 	job->cancel_fn = NULL;
-	AIO_UNLOCK(ki);
 	return (true);
 }
 
 bool
-aio_set_cancel_function(struct kaiocb *job, aio_cancel_fn_t *func)
+aio_clear_cancel_function(struct kaiocb *job)
 {
 	struct kaioinfo *ki;
+	bool ret;
 
 	ki = job->userproc->p_aioinfo;
 	AIO_LOCK(ki);
-	if (job->jobflags & KAIOCB_CANCELLED) {
-		AIO_UNLOCK(ki);
+	ret = aio_clear_cancel_function_locked(job);
+	AIO_UNLOCK(ki);
+	return (ret);
+}
+
+static bool
+aio_set_cancel_function_locked(struct kaiocb *job, aio_cancel_fn_t *func)
+{
+
+	AIO_LOCK_ASSERT(job->userproc->p_aioinfo, MA_OWNED);
+	if (job->jobflags & KAIOCB_CANCELLED)
 		return (false);
-	}
 	job->cancel_fn = func;
-	AIO_UNLOCK(ki);
 	return (true);
 }
 
+bool
+aio_set_cancel_function(struct kaiocb *job, aio_cancel_fn_t *func)
+{
+	struct kaioinfo *ki;
+	bool ret;
+
+	ki = job->userproc->p_aioinfo;
+	AIO_LOCK(ki);
+	ret = aio_set_cancel_function_locked(job, func);
+	AIO_UNLOCK(ki);
+	return (ret);
+}
+
 void
 aio_complete(struct kaiocb *job, long status, int error)
 {
@@ -1655,10 +1673,10 @@
 	struct kaioinfo *ki;
 
 	ki = job->userproc->p_aioinfo;
-	mtx_lock(&aio_job_mtx);
+	AIO_LOCK(ki);
 	if (!aio_cancel_cleared(job))
 		TAILQ_REMOVE(&ki->kaio_syncqueue, job, list);
-	mtx_unlock(&aio_job_mtx);
+	AIO_UNLOCK(ki);
 	aio_cancel(job);
 }
 
@@ -1718,7 +1736,8 @@
 			}
 		}
 		if (job->pending != 0) {
-			if (!aio_set_cancel_function(job, aio_cancel_sync)) {
+			if (!aio_set_cancel_function_locked(job,
+				aio_cancel_sync)) {
 				AIO_UNLOCK(ki);
 				aio_cancel(job);
 				return (0);
Index: head/tests/sys/aio/aio_test.c
===================================================================
--- head/tests/sys/aio/aio_test.c
+++ head/tests/sys/aio/aio_test.c
@@ -924,6 +924,88 @@
 	close(s[0]);
 }
 
+/*
+ * This test just performs a basic test of aio_fsync().
+ */
+ATF_TC_WITHOUT_HEAD(aio_fsync_test);
+ATF_TC_BODY(aio_fsync_test, tc)
+{
+	struct aiocb synccb, *iocbp;
+	struct {
+		struct aiocb iocb;
+		bool done;
+		char *buffer;
+	} buffers[16];
+	struct stat sb;
+	char pathname[PATH_MAX];
+	ssize_t rval;
+	unsigned i;
+	int fd;
+
+	ATF_REQUIRE_KERNEL_MODULE("aio");
+	ATF_REQUIRE_UNSAFE_AIO();
+
+	strcpy(pathname, PATH_TEMPLATE);
+	fd = mkstemp(pathname);
+	ATF_REQUIRE_MSG(fd != -1, "mkstemp failed: %s", strerror(errno));
+	unlink(pathname);
+
+	ATF_REQUIRE(fstat(fd, &sb) == 0);
+	ATF_REQUIRE(sb.st_blksize != 0);
+	ATF_REQUIRE(ftruncate(fd, sb.st_blksize * nitems(buffers)) == 0);
+
+	/*
+	 * Queue several asynchronous write requests.  Hopefully this
+	 * forces the aio_fsync() request to be deferred.  There is no
+	 * reliable way to guarantee that however.
+	 */
+	srandomdev();
+	for (i = 0; i < nitems(buffers); i++) {
+		buffers[i].done = false;
+		memset(&buffers[i].iocb, 0, sizeof(buffers[i].iocb));
+		buffers[i].buffer = malloc(sb.st_blksize);
+		aio_fill_buffer(buffers[i].buffer, sb.st_blksize, random());
+		buffers[i].iocb.aio_fildes = fd;
+		buffers[i].iocb.aio_buf = buffers[i].buffer;
+		buffers[i].iocb.aio_nbytes = sb.st_blksize;
+		buffers[i].iocb.aio_offset = sb.st_blksize * i;
+		ATF_REQUIRE(aio_write(&buffers[i].iocb) == 0);
+	}
+
+	/* Queue the aio_fsync request. */
+	memset(&synccb, 0, sizeof(synccb));
+	synccb.aio_fildes = fd;
+	ATF_REQUIRE(aio_fsync(O_SYNC, &synccb) == 0);
+
+	/* Wait for requests to complete. */
+	for (;;) {
+	next:
+		rval = aio_waitcomplete(&iocbp, NULL);
+		ATF_REQUIRE(iocbp != NULL);
+		if (iocbp == &synccb) {
+			ATF_REQUIRE(rval == 0);
+			break;
+		}
+
+		for (i = 0; i < nitems(buffers); i++) {
+			if (iocbp == &buffers[i].iocb) {
+				ATF_REQUIRE(buffers[i].done == false);
+				ATF_REQUIRE(rval == sb.st_blksize);
+				buffers[i].done = true;
+				goto next;
+			}
+		}
+
+		ATF_REQUIRE_MSG(false, "unmatched AIO request");
+	}
+
+	for (i = 0; i < nitems(buffers); i++)
+		ATF_REQUIRE_MSG(buffers[i].done,
+		    "AIO request %u did not complete", i);
+
+	close(fd);
+}
+
 ATF_TP_ADD_TCS(tp)
 {
 
@@ -937,6 +1019,7 @@
 	ATF_TP_ADD_TC(tp, aio_socket_two_reads);
 	ATF_TP_ADD_TC(tp, aio_socket_blocking_short_write);
 	ATF_TP_ADD_TC(tp, aio_socket_short_write_cancel);
+	ATF_TP_ADD_TC(tp, aio_fsync_test);
 
 	return (atf_no_error());
 }