iget/iget5: don't bother with ->i_lock until we find a match

Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

Documentation/filesystems/porting

@@ -455,3 +455,11 @@ in your dentry operations instead.
 	vfs_follow_link has been removed.  Filesystems must use nd_set_link
 	from ->follow_link for normal symlinks, or nd_jump_link for magic
 	/proc/<pid> style links.
+--
+[mandatory]
+	iget5_locked()/ilookup5()/ilookup5_nowait() test() callback used to be
+	called with both ->i_lock and inode_hash_lock held; the former is *not*
+	taken anymore, so verify that your callbacks do not rely on it (none
+	of the in-tree instances did).  inode_hash_lock is still held,
+	of course, so they are still serialized wrt removal from inode hash,
+	as well as wrt set() callback of iget5_locked().

drivers/staging/lustre/lustre/llite/namei.c

@@ -83,7 +83,7 @@ int ll_unlock(__u32 mode, struct lustre_handle *lockh)
 }
 
 
-/* called from iget5_locked->find_inode() under inode_lock spinlock */
+/* called from iget5_locked->find_inode() under inode_hash_lock spinlock */
 static int ll_test_inode(struct inode *inode, void *opaque)
 {
 	struct ll_inode_info *lli = ll_i2info(inode);

fs/inode.c

@@ -773,15 +773,11 @@ static struct inode *find_inode(struct super_block *sb,
 
 repeat:
 	hlist_for_each_entry(inode, head, i_hash) {
-		spin_lock(&inode->i_lock);
-		if (inode->i_sb != sb) {
-			spin_unlock(&inode->i_lock);
+		if (inode->i_sb != sb)
 			continue;
-		}
-		if (!test(inode, data)) {
-			spin_unlock(&inode->i_lock);
+		if (!test(inode, data))
 			continue;
-		}
+		spin_lock(&inode->i_lock);
 		if (inode->i_state & (I_FREEING|I_WILL_FREE)) {
 			__wait_on_freeing_inode(inode);
 			goto repeat;
@@ -804,15 +800,11 @@ static struct inode *find_inode_fast(struct super_block *sb,
 
 repeat:
 	hlist_for_each_entry(inode, head, i_hash) {
-		spin_lock(&inode->i_lock);
-		if (inode->i_ino != ino) {
-			spin_unlock(&inode->i_lock);
+		if (inode->i_ino != ino)
 			continue;
-		}
-		if (inode->i_sb != sb) {
-			spin_unlock(&inode->i_lock);
+		if (inode->i_sb != sb)
 			continue;
-		}
+		spin_lock(&inode->i_lock);
 		if (inode->i_state & (I_FREEING|I_WILL_FREE)) {
 			__wait_on_freeing_inode(inode);
 			goto repeat;

fs/ntfs/inode.c

@@ -55,7 +55,7 @@
  *
  * Return 1 if the attributes match and 0 if not.
  *
- * NOTE: This function runs with the inode->i_lock spin lock held so it is not
+ * NOTE: This function runs with the inode_hash_lock spin lock held so it is not
  * allowed to sleep.
  */
 int ntfs_test_inode(struct inode *vi, ntfs_attr *na)