Small bug with offline cpus

[Maxime Villard <max%m00nbsd.net@localhost>]

Hi,
a bug I must have spotted some weeks ago: the kernel decrements the
number of offline cpus even when trying to shutting down one fails.
How to reproduce:

	# schedctl -p SOME_RANDOM_PROC_PID -A 0
	# sysctl hw.ncpuonline
	# cpuctl offline 0     (it fails)
	# sysctl hw.ncpuonline (one cpu missing)

If you cpuctl too much, the value goes negative. This is not a harmful
bug.

Index: kern_cpu.c
===================================================================
RCS file: /cvsroot/src/sys/kern/kern_cpu.c,v
retrieving revision 1.70
diff -u -r1.70 kern_cpu.c
--- kern_cpu.c	20 Aug 2015 09:45:45 -0000	1.70
+++ kern_cpu.c	28 Aug 2015 08:51:36 -0000
@@ -444,7 +444,6 @@
 		if ((spc->spc_flags & SPCF_OFFLINE) == 0)
 			return 0;
 		func = (xcfunc_t)cpu_xc_online;
-		ncpuonline++;
 	} else {
 		if ((spc->spc_flags & SPCF_OFFLINE) != 0)
 			return 0;
@@ -463,16 +462,19 @@
 		if (nonline == 1)
 			return EBUSY;
 		func = (xcfunc_t)cpu_xc_offline;
-		ncpuonline--;
 	}
 
 	where = xc_unicast(0, func, ci, NULL, ci);
 	xc_wait(where);
 	if (online) {
 		KASSERT((spc->spc_flags & SPCF_OFFLINE) == 0);
-	} else if ((spc->spc_flags & SPCF_OFFLINE) == 0) {
-		/* If was not set offline, then it is busy */
-		return EBUSY;
+		ncpuonline++;
+	} else {
+		if ((spc->spc_flags & SPCF_OFFLINE) == 0) {
+			/* If was not set offline, then it is busy */
+			return EBUSY;
+		}
+		ncpuonline--;
 	}
 
 	spc->spc_lastmod = time_second;


Ok?

Maxime