Revert "fs: use RCU read side protection in d_validate"

This reverts commit 3825bdb7ed920845961f32f364454bee5f469abb.

You cannot dget() a dentry without having a reference, or holding
a lock that guarantees it remains valid.

Signed-off-by: Nick Piggin <npiggin@kernel.dk>

1 files changed, 19 insertions, 12 deletions

diff --git a/fs/dcache.c b/fs/dcache.c
index 23702a9d4e6d..cc2b93802179 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1491,26 +1491,33 @@ out:
  * This is used by ncpfs in its readdir implementation.
  * Zero is returned in the dentry is invalid.
  */
-int d_validate(struct dentry *dentry, struct dentry *parent)
+ 
+int d_validate(struct dentry *dentry, struct dentry *dparent)
 {
-        struct hlist_head *head = d_hash(parent, dentry->d_name.hash);
-        struct hlist_node *node;
-        struct dentry *d;
+        struct hlist_head *base;
+        struct hlist_node *lhp;
 
         /* Check whether the ptr might be valid at all.. */
         if (!kmem_ptr_validate(dentry_cache, dentry))
-                return 0;
-        if (dentry->d_parent != parent)
-                return 0;
+                goto out;
 
-        rcu_read_lock();
-        hlist_for_each_entry_rcu(d, node, head, d_hash) {
-                if (d == dentry) {
-                        dget(dentry);
+        if (dentry->d_parent != dparent)
+                goto out;
+
+        spin_lock(&dcache_lock);
+        base = d_hash(dparent, dentry->d_name.hash);
+        hlist_for_each(lhp,base) { 
+                /* hlist_for_each_entry_rcu() not required for d_hash list
+                 * as it is parsed under dcache_lock
+                 */
+                if (dentry == hlist_entry(lhp, struct dentry, d_hash)) {
+                        __dget_locked(dentry);
+                        spin_unlock(&dcache_lock);
                         return 1;
                 }
         }
-        rcu_read_unlock();
+        spin_unlock(&dcache_lock);
+out:
         return 0;
 }
 EXPORT_SYMBOL(d_validate);