From 16e8d96ddae3122fb70a5e36beb47ccd64f6246c Mon Sep 17 00:00:00 2001
From: imp <imp@FreeBSD.org>
Date: Wed, 21 Mar 2018 14:46:54 +0000
Subject: [PATCH] Remove Giant from init creation and vfs_mountroot.

Sponsored by: Netflix
Discussed with: kib@, mckusick@
Differential Review: https://reviews.freebsd.org/D14712
---
 sys/kern/init_main.c     |  5 -----
 sys/kern/kern_shutdown.c |  7 ++-----
 sys/kern/vfs_mountroot.c | 12 ++----------
 3 files changed, 4 insertions(+), 20 deletions(-)

diff --git a/sys/kern/init_main.c b/sys/kern/init_main.c
index ac856d10fab9..3c11fcd365f0 100644
--- a/sys/kern/init_main.c
+++ b/sys/kern/init_main.c
@@ -703,10 +703,6 @@ start_init(void *dummy)
 	struct thread *td;
 	struct proc *p;
 
-	mtx_lock(&Giant);
-
-	GIANT_REQUIRED;
-
 	TSENTER();	/* Here so we don't overlap with mi_startup. */
 
 	td = curthread;
@@ -801,7 +797,6 @@ start_init(void *dummy)
 		 * to user mode as init!
 		 */
 		if ((error = sys_execve(td, &args)) == EJUSTRETURN) {
-			mtx_unlock(&Giant);
 			TSEXIT();
 			return;
 		}
diff --git a/sys/kern/kern_shutdown.c b/sys/kern/kern_shutdown.c
index 71d4484782fe..e5ea9644ad3f 100644
--- a/sys/kern/kern_shutdown.c
+++ b/sys/kern/kern_shutdown.c
@@ -268,13 +268,10 @@ sys_reboot(struct thread *td, struct reboot_args *uap)
 	if (error == 0)
 		error = priv_check(td, PRIV_REBOOT);
 	if (error == 0) {
-		if (uap->opt & RB_REROOT) {
+		if (uap->opt & RB_REROOT)
 			error = kern_reroot();
-		} else {
-			mtx_lock(&Giant);
+		else
 			kern_reboot(uap->opt);
-			mtx_unlock(&Giant);
-		}
 	}
 	return (error);
 }
diff --git a/sys/kern/vfs_mountroot.c b/sys/kern/vfs_mountroot.c
index 3c50d0f5e606..0b41cb7a7e44 100644
--- a/sys/kern/vfs_mountroot.c
+++ b/sys/kern/vfs_mountroot.c
@@ -579,9 +579,7 @@ parse_dir_md(char **conf)
 
 	if (root_mount_mddev != -1) {
 		mdio->md_unit = root_mount_mddev;
-		DROP_GIANT();
 		error = kern_ioctl(td, fd, MDIOCDETACH, (void *)mdio);
-		PICKUP_GIANT();
 		/* Ignore errors. We don't care. */
 		root_mount_mddev = -1;
 	}
@@ -590,9 +588,7 @@ parse_dir_md(char **conf)
 	mdio->md_options = MD_AUTOUNIT | MD_READONLY;
 	mdio->md_mediasize = sb.st_size;
 	mdio->md_unit = 0;
-	DROP_GIANT();
 	error = kern_ioctl(td, fd, MDIOCATTACH, (void *)mdio);
-	PICKUP_GIANT();
 	if (error)
 		goto out;
 
@@ -601,9 +597,7 @@ parse_dir_md(char **conf)
 		mdio->md_file = NULL;
 		mdio->md_options = 0;
 		mdio->md_mediasize = 0;
-		DROP_GIANT();
 		error = kern_ioctl(td, fd, MDIOCDETACH, (void *)mdio);
-		PICKUP_GIANT();
 		/* Ignore errors. We don't care. */
 		error = ERANGE;
 		goto out;
@@ -960,9 +954,7 @@ vfs_mountroot_wait(void)
 
 	curfail = 0;
 	while (1) {
-		DROP_GIANT();
 		g_waitidle();
-		PICKUP_GIANT();
 		mtx_lock(&root_holds_mtx);
 		if (LIST_EMPTY(&root_holds)) {
 			mtx_unlock(&root_holds_mtx);
@@ -1004,9 +996,7 @@ vfs_mountroot_wait_if_neccessary(const char *fs, const char *dev)
 	 * Note that we must wait for GEOM to finish reconfiguring itself,
 	 * eg for geom_part(4) to finish tasting.
 	 */
-	DROP_GIANT();
 	g_waitidle();
-	PICKUP_GIANT();
 	if (parse_mount_dev_present(dev))
 		return (0);
 
@@ -1038,6 +1028,8 @@ vfs_mountroot(void)
 	time_t timebase;
 	int error;
 	
+	mtx_assert(&Giant, MA_NOTOWNED);
+
 	TSENTER();
 
 	td = curthread;