[PATCH] Re: 2.5.11 breakage

	OK, here comes.  Patch below is an attempt to do the fastwalk
stuff in right way and so far it seems to be working.

 - dentry leak is plugged
 - locked/unlocked state of nameidata doesn't depend on history - it
   depends only on point in code.
 - LOOKUP_LOCKED is gone.
 - following mounts and .. doesn't drop dcache_lock
 - light-weight permission check distinguishes between "don't know" and
   "permission denied", so we don't call full-blown permission() unless
   we have to.
 - code that changes root/pwd holds dcache_lock _and_ write lock on
   current->fs->lock.  I.e. if we hold dcache_lock we can safely
   access our ->fs->{root,pwd}{,mnt}
 - __d_lookup() does not increment refcount; callers do dget_locked()
   if they need it (behaviour of d_lookup() didn't change, obviously).
 - link_path_walk() logics had been (somewhat) cleaned up.

fs/dcache.c

@@ -849,6 +849,8 @@ struct dentry * d_lookup(struct dentry * parent, struct qstr * name)
 	struct dentry * dentry;
 	spin_lock(&dcache_lock);
 	dentry = __d_lookup(parent,name);
+	if (dentry)
+		__dget_locked(dentry);
 	spin_unlock(&dcache_lock);
 	return dentry;
 }
@@ -881,7 +883,6 @@ struct dentry * __d_lookup(struct dentry * parent, struct qstr * name)
 			if (memcmp(dentry->d_name.name, str, len))
 				continue;
 		}
-		__dget_locked(dentry);
 		dentry->d_vfs_flags |= DCACHE_REFERENCED;
 		return dentry;
 	}

include/linux/fs.h

@@ -654,6 +654,8 @@ struct nameidata {
 	struct qstr last;
 	unsigned int flags;
 	int last_type;
+	struct dentry *old_dentry;
+	struct vfsmount *old_mnt;
 };
 
 #define DQUOT_USR_ENABLED	0x01		/* User diskquotas enabled */
@@ -1395,7 +1397,6 @@ extern ino_t find_inode_number(struct dentry *, struct qstr *);
 #define LOOKUP_CONTINUE		(4)
 #define LOOKUP_PARENT		(16)
 #define LOOKUP_NOALT		(32)
-#define LOOKUP_LOCKED		(64)
 
 /*
  * Type of the last component on LOOKUP_PARENT

include/linux/fs_struct.h

@@ -35,10 +35,12 @@ static inline void set_fs_root(struct fs_struct *fs,
 	struct dentry *old_root;
 	struct vfsmount *old_rootmnt;
 	write_lock(&fs->lock);
+	spin_lock(&dcache_lock);
 	old_root = fs->root;
 	old_rootmnt = fs->rootmnt;
 	fs->rootmnt = mntget(mnt);
 	fs->root = dget(dentry);
+	spin_unlock(&dcache_lock);
 	write_unlock(&fs->lock);
 	if (old_root) {
 		dput(old_root);
@@ -58,10 +60,12 @@ static inline void set_fs_pwd(struct fs_struct *fs,
 	struct dentry *old_pwd;
 	struct vfsmount *old_pwdmnt;
 	write_lock(&fs->lock);
+	spin_lock(&dcache_lock);
 	old_pwd = fs->pwd;
 	old_pwdmnt = fs->pwdmnt;
 	fs->pwdmnt = mntget(mnt);
 	fs->pwd = dget(dentry);
+	spin_unlock(&dcache_lock);
 	write_unlock(&fs->lock);
 	if (old_pwd) {
 		dput(old_pwd);