powerpc/pseries: Verify CPU doesn't exist before adding

When DLPAR adding a CPU we should verify that the CPU does not already
exist. Failure to do so can generate a kernel oops;

[    9.465585] kernel BUG at arch/powerpc/platforms/pseries/dlpar.c:382!
[    9.465796] Oops: Exception in kernel mode, sig: 5 [#1]

This oops can be generated by causing a probe to be performed on a cpu
by writing to the sysfs cpu probe file (/sys/devices/system/cpu/probe).
This patch adds a check for the existence of cpu prior to probing the cpu
so userspace doing the wrong thing won't trigger a BUG_ON().

Signed-off-by: Nathan Fontenot <nfont@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/arch/powerpc/platforms/pseries/dlpar.c b/arch/powerpc/platforms/pseries/dlpar.c
index f244dcb..fe6320d 100644 (file)
--- a/arch/powerpc/platforms/pseries/dlpar.c
+++ b/arch/powerpc/platforms/pseries/dlpar.c
@@ -381,6 +381,32 @@ out:
 
 }
 
+static bool dlpar_cpu_exists(struct device_node *parent, u32 drc_index)
+{
+       struct device_node *child = NULL;
+       u32 my_drc_index;
+       bool found;
+       int rc;
+
+       /* Assume cpu doesn't exist */
+       found = false;
+
+       for_each_child_of_node(parent, child) {
+               rc = of_property_read_u32(child, "ibm,my-drc-index",
+                                         &my_drc_index);
+               if (rc)
+                       continue;
+
+               if (my_drc_index == drc_index) {
+                       of_node_put(child);
+                       found = true;
+                       break;
+               }
+       }
+
+       return found;
+}
+
 static ssize_t dlpar_cpu_probe(const char *buf, size_t count)
 {
        struct device_node *dn, *parent;
@@ -391,14 +417,23 @@ static ssize_t dlpar_cpu_probe(const char *buf, size_t count)
        if (rc)
                return -EINVAL;
 
-       rc = dlpar_acquire_drc(drc_index);
-       if (rc)
-               return -EINVAL;
-
        parent = of_find_node_by_path("/cpus");
        if (!parent)
                return -ENODEV;
 
+       if (dlpar_cpu_exists(parent, drc_index)) {
+               of_node_put(parent);
+               printk(KERN_WARNING "CPU with drc index %x already exists\n",
+                      drc_index);
+               return -EINVAL;
+       }
+
+       rc = dlpar_acquire_drc(drc_index);
+       if (rc) {
+               of_node_put(parent);
+               return -EINVAL;
+       }
+
        dn = dlpar_configure_connector(cpu_to_be32(drc_index), parent);
        of_node_put(parent);
        if (!dn) {