of: __of_detach_node() - remove node from phandle cache

Non-overlay dynamic devicetree node removal may leave the node in
the phandle cache.  Subsequent calls to of_find_node_by_phandle()
will incorrectly find the stale entry.  Remove the node from the
cache.

Add paranoia checks in of_find_node_by_phandle() as a second level
of defense (do not return cached node if detached, do not add node
to cache if detached).

Fixes: 0b3ce78e90fc ("of: cache phandle nodes to reduce cost of of_find_node_by_phandle()")
Reported-by: Michael Bringmann <mwb@linux.vnet.ibm.com>
Cc: stable@vger.kernel.org # v4.17+
Signed-off-by: Frank Rowand <frank.rowand@sony.com>
Signed-off-by: Rob Herring <robh@kernel.org>

3 files changed, 37 insertions, 1 deletions

diff --git a/drivers/of/base.c b/drivers/of/base.c
index 4da1c688995b..5226e898476e 100644
--- a/drivers/of/base.c
+++ b/drivers/of/base.c
@@ -169,6 +169,28 @@ int of_free_phandle_cache(void)
 late_initcall_sync(of_free_phandle_cache);
 #endif
 
+/*
+ * Caller must hold devtree_lock.
+ */
+void __of_free_phandle_cache_entry(phandle handle)
+{
+        phandle masked_handle;
+        struct device_node *np;
+
+        if (!handle)
+                return;
+
+        masked_handle = handle & phandle_cache_mask;
+
+        if (phandle_cache) {
+                np = phandle_cache[masked_handle];
+                if (np && handle == np->phandle) {
+                        of_node_put(np);
+                        phandle_cache[masked_handle] = NULL;
+                }
+        }
+}
+
 void of_populate_phandle_cache(void)
 {
         unsigned long flags;
@@ -1214,11 +1236,18 @@ struct device_node *of_find_node_by_phandle(phandle handle)
                 if (phandle_cache[masked_handle] &&
                     handle == phandle_cache[masked_handle]->phandle)
                         np = phandle_cache[masked_handle];
+                if (np && of_node_check_flag(np, OF_DETACHED)) {
+                        WARN_ON(1); /* did not uncache np on node removal */
+                        of_node_put(np);
+                        phandle_cache[masked_handle] = NULL;
+                        np = NULL;
+                }
         }
 
         if (!np) {
                 for_each_of_allnodes(np)
-                        if (np->phandle == handle) {
+                        if (np->phandle == handle &&
+                            !of_node_check_flag(np, OF_DETACHED)) {
                                 if (phandle_cache) {
                                         /* will put when removed from cache */
                                         of_node_get(np);
diff --git a/drivers/of/dynamic.c b/drivers/of/dynamic.c
index b4e5b90cb314..a09c1c3cf831 100644
--- a/drivers/of/dynamic.c
+++ b/drivers/of/dynamic.c
@@ -277,6 +277,9 @@ void __of_detach_node(struct device_node *np)
         }
 
         of_node_set_flag(np, OF_DETACHED);
+
+        /* race with of_find_node_by_phandle() prevented by devtree_lock */
+        __of_free_phandle_cache_entry(np->phandle);
 }
 
 /**
diff --git a/drivers/of/of_private.h b/drivers/of/of_private.h
index 5d1567025358..24786818e32e 100644
--- a/drivers/of/of_private.h
+++ b/drivers/of/of_private.h
@@ -84,6 +84,10 @@ static inline void __of_detach_node_sysfs(struct device_node *np) {}
 int of_resolve_phandles(struct device_node *tree);
 #endif
 
+#if defined(CONFIG_OF_DYNAMIC)
+void __of_free_phandle_cache_entry(phandle handle);
+#endif
+
 #if defined(CONFIG_OF_OVERLAY)
 void of_overlay_mutex_lock(void);
 void of_overlay_mutex_unlock(void);