Small bug with offline cpus

[Maxime Villard]

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