fs: use RCU read side protection in d_validate

d_validate does a purely read lookup in the dentry hash, so use RCU read side
locking instead of dcache_lock.  Split out from a larget patch by
Nick Piggin <npiggin@suse.de>.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 12 insertions, 19 deletions

diff --git a/fs/dcache.c b/fs/dcache.c
index cc2b93802179..23702a9d4e6d 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1491,33 +1491,26 @@ 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 *dparent)
+int d_validate(struct dentry *dentry, struct dentry *parent)
 {
-        struct hlist_head *base;
-        struct hlist_node *lhp;
+        struct hlist_head *head = d_hash(parent, dentry->d_name.hash);
+        struct hlist_node *node;
+        struct dentry *d;
 
         /* Check whether the ptr might be valid at all.. */
         if (!kmem_ptr_validate(dentry_cache, dentry))
-                goto out;
-
-        if (dentry->d_parent != dparent)
-                goto out;
+                return 0;
+        if (dentry->d_parent != parent)
+                return 0;
 
-        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);
+        rcu_read_lock();
+        hlist_for_each_entry_rcu(d, node, head, d_hash) {
+                if (d == dentry) {
+                        dget(dentry);
                         return 1;
                 }
         }
-        spin_unlock(&dcache_lock);
-out:
+        rcu_read_unlock();
         return 0;
 }
 EXPORT_SYMBOL(d_validate);