push kernel lock down in ifioctl()

[Klemens Nanni]

Not all interface ioctls need the kernel lock, but they all grab it.

Here's a mechanical diff splitting the single lock/unlock around
ifioctl() into individual lock/unlock dances inside ifioctl().

>From there we can unlock individual ioctls piece by piece.

Survives regress on sparc64 and didn't blow up on my amd64 notebook yet.

Feedback? Objection? OK?


Index: net/if.c
===================================================================
RCS file: /cvs/src/sys/net/if.c,v
retrieving revision 1.665
diff -u -p -r1.665 if.c
--- net/if.c    8 Sep 2022 10:22:06 -0000       1.665
+++ net/if.c    7 Nov 2022 15:13:01 -0000
@@ -1942,19 +1942,25 @@ ifioctl(struct socket *so, u_long cmd, c
        case SIOCIFCREATE:
                if ((error = suser(p)) != 0)
                        return (error);
+               KERNEL_LOCK();
                error = if_clone_create(ifr->ifr_name, 0);
+               KERNEL_UNLOCK();
                return (error);
        case SIOCIFDESTROY:
                if ((error = suser(p)) != 0)
                        return (error);
+               KERNEL_LOCK();
                error = if_clone_destroy(ifr->ifr_name);
+               KERNEL_UNLOCK();
                return (error);
        case SIOCSIFGATTR:
                if ((error = suser(p)) != 0)
                        return (error);
+               KERNEL_LOCK();
                NET_LOCK();
                error = if_setgroupattribs(data);
                NET_UNLOCK();
+               KERNEL_UNLOCK();
                return (error);
        case SIOCGIFCONF:
        case SIOCIFGCLONERS:
@@ -1973,12 +1979,19 @@ ifioctl(struct socket *so, u_long cmd, c
        case SIOCGIFRDOMAIN:
        case SIOCGIFGROUP:
        case SIOCGIFLLPRIO:
-               return (ifioctl_get(cmd, data));
+               KERNEL_LOCK();
+               error = ifioctl_get(cmd, data);
+               KERNEL_UNLOCK();
+               return (error);
        }
 
+       KERNEL_LOCK();
+
        ifp = if_unit(ifr->ifr_name);
-       if (ifp == NULL)
+       if (ifp == NULL) {
+               KERNEL_UNLOCK();
                return (ENXIO);
+       }
        oif_flags = ifp->if_flags;
        oif_xflags = ifp->if_xflags;
 
@@ -2396,6 +2409,8 @@ forceup:
 
        if (((oif_flags ^ ifp->if_flags) & IFF_UP) != 0)
                getmicrotime(&ifp->if_lastchange);
+
+       KERNEL_UNLOCK();
 
        if_put(ifp);