powerpc/pseries: Correct rtas_data_buf locking in dlpar code

The dlpar code can cause a deadlock to occur when making the RTAS
configure-connector call.  This occurs because we make kmalloc calls,
which can block, while parsing the rtas_data_buf and holding the
rtas_data_buf_lock.  This an cause issues if someone else attempts
to grab the rtas_data_bug_lock.

This patch alleviates this issue by copying the contents of the rtas_data_buf
to a local buffer before parsing.  This allows us to only hold the
rtas_data_buf_lock around the RTAS configure-connector calls.

Signed-off-by: Nathan Fontenot <nfont@austin.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 29 insertions, 13 deletions

diff --git a/arch/powerpc/platforms/pseries/dlpar.c b/arch/powerpc/platforms/pseries/dlpar.c
index 227c1c3d585e..72d8054fa739 100644
--- a/arch/powerpc/platforms/pseries/dlpar.c
+++ b/arch/powerpc/platforms/pseries/dlpar.c
@@ -129,20 +129,35 @@ struct device_node *dlpar_configure_connector(u32 drc_index)
         struct property *property;
         struct property *last_property = NULL;
         struct cc_workarea *ccwa;
+        char *data_buf;
         int cc_token;
-        int rc;
+        int rc = -1;
 
         cc_token = rtas_token("ibm,configure-connector");
         if (cc_token == RTAS_UNKNOWN_SERVICE)
                 return NULL;
 
-        spin_lock(&rtas_data_buf_lock);
-        ccwa = (struct cc_workarea *)&rtas_data_buf[0];
+        data_buf = kzalloc(RTAS_DATA_BUF_SIZE, GFP_KERNEL);
+        if (!data_buf)
+                return NULL;
+
+        ccwa = (struct cc_workarea *)&data_buf[0];
         ccwa->drc_index = drc_index;
         ccwa->zero = 0;
 
-        rc = rtas_call(cc_token, 2, 1, NULL, rtas_data_buf, NULL);
-        while (rc) {
+        do {
+                /* Since we release the rtas_data_buf lock between configure
+                 * connector calls we want to re-populate the rtas_data_buffer
+                 * with the contents of the previous call.
+                 */
+                spin_lock(&rtas_data_buf_lock);
+
+                memcpy(rtas_data_buf, data_buf, RTAS_DATA_BUF_SIZE);
+                rc = rtas_call(cc_token, 2, 1, NULL, rtas_data_buf, NULL);
+                memcpy(data_buf, rtas_data_buf, RTAS_DATA_BUF_SIZE);
+
+                spin_unlock(&rtas_data_buf_lock);
+
                 switch (rc) {
                 case NEXT_SIBLING:
                         dn = dlpar_parse_cc_node(ccwa);
@@ -197,18 +212,19 @@ struct device_node *dlpar_configure_connector(u32 drc_index)
                                "returned from configure-connector\n", rc);
                         goto cc_error;
                 }
+        } while (rc);
 
-                rc = rtas_call(cc_token, 2, 1, NULL, rtas_data_buf, NULL);
+cc_error:
+        kfree(data_buf);
+
+        if (rc) {
+                if (first_dn)
+                        dlpar_free_cc_nodes(first_dn);
+
+                return NULL;
         }
 
-        spin_unlock(&rtas_data_buf_lock);
         return first_dn;
-
-cc_error:
-        if (first_dn)
-                dlpar_free_cc_nodes(first_dn);
-        spin_unlock(&rtas_data_buf_lock);
-        return NULL;
 }
 
 static struct device_node *derive_parent(const char *path)