consolidate nameidata_..._drop_rcu()

Merge these into a single function (unlazy_walk(nd, dentry)),
kill ..._maybe variants

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

1 files changed, 46 insertions, 105 deletions

diff --git a/fs/namei.c b/fs/namei.c
index 54fc993e3027..1039cbae0c12 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -391,79 +391,28 @@ void path_put(struct path *path)
 }
 EXPORT_SYMBOL(path_put);
 
-/**
- * nameidata_drop_rcu - drop this nameidata out of rcu-walk
- * @nd: nameidata pathwalk data to drop
- * Returns: 0 on success, -ECHILD on failure
- *
+/*
  * Path walking has 2 modes, rcu-walk and ref-walk (see
- * Documentation/filesystems/path-lookup.txt). __drop_rcu* functions attempt
- * to drop out of rcu-walk mode and take normal reference counts on dentries
- * and vfsmounts to transition to rcu-walk mode. __drop_rcu* functions take
- * refcounts at the last known good point before rcu-walk got stuck, so
- * ref-walk may continue from there. If this is not successful (eg. a seqcount
- * has changed), then failure is returned and path walk restarts from the
- * beginning in ref-walk mode.
- *
- * nameidata_drop_rcu attempts to drop the current nd->path and nd->root into
- * ref-walk. Must be called from rcu-walk context.
+ * Documentation/filesystems/path-lookup.txt).  In situations when we can't
+ * continue in RCU mode, we attempt to drop out of rcu-walk mode and grab
+ * normal reference counts on dentries and vfsmounts to transition to rcu-walk
+ * mode.  Refcounts are grabbed at the last known good point before rcu-walk
+ * got stuck, so ref-walk may continue from there. If this is not successful
+ * (eg. a seqcount has changed), then failure is returned and it's up to caller
+ * to restart the path walk from the beginning in ref-walk mode.
  */
-static int nameidata_drop_rcu(struct nameidata *nd)
-{
-        struct fs_struct *fs = current->fs;
-        struct dentry *dentry = nd->path.dentry;
-        int want_root = 0;
-
-        BUG_ON(!(nd->flags & LOOKUP_RCU));
-        if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT)) {
-                want_root = 1;
-                spin_lock(&fs->lock);
-                if (nd->root.mnt != fs->root.mnt ||
-                                nd->root.dentry != fs->root.dentry)
-                        goto err_root;
-        }
-        spin_lock(&dentry->d_lock);
-        if (!__d_rcu_to_refcount(dentry, nd->seq))
-                goto err;
-        BUG_ON(nd->inode != dentry->d_inode);
-        spin_unlock(&dentry->d_lock);
-        if (want_root) {
-                path_get(&nd->root);
-                spin_unlock(&fs->lock);
-        }
-        mntget(nd->path.mnt);
-
-        rcu_read_unlock();
-        br_read_unlock(vfsmount_lock);
-        nd->flags &= ~LOOKUP_RCU;
-        return 0;
-err:
-        spin_unlock(&dentry->d_lock);
-err_root:
-        if (want_root)
-                spin_unlock(&fs->lock);
-        return -ECHILD;
-}
-
-/* Try to drop out of rcu-walk mode if we were in it, otherwise do nothing.  */
-static inline int nameidata_drop_rcu_maybe(struct nameidata *nd)
-{
-        if (nd->flags & LOOKUP_RCU)
-                return nameidata_drop_rcu(nd);
-        return 0;
-}
 
 /**
- * nameidata_dentry_drop_rcu - drop nameidata and dentry out of rcu-walk
- * @nd: nameidata pathwalk data to drop
- * @dentry: dentry to drop
+ * unlazy_walk - try to switch to ref-walk mode.
+ * @nd: nameidata pathwalk data
+ * @dentry: child of nd->path.dentry or NULL
  * Returns: 0 on success, -ECHILD on failure
  *
- * nameidata_dentry_drop_rcu attempts to drop the current nd->path and nd->root,
- * and dentry into ref-walk. @dentry must be a path found by a do_lookup call on
- * @nd. Must be called from rcu-walk context.
+ * unlazy_walk attempts to legitimize the current nd->path, nd->root and dentry
+ * for ref-walk mode.  @dentry must be a path found by a do_lookup call on
+ * @nd or NULL.  Must be called from rcu-walk context.
  */
-static int nameidata_dentry_drop_rcu(struct nameidata *nd, struct dentry *dentry)
+static int unlazy_walk(struct nameidata *nd, struct dentry *dentry)
 {
         struct fs_struct *fs = current->fs;
         struct dentry *parent = nd->path.dentry;
@@ -478,18 +427,25 @@ static int nameidata_dentry_drop_rcu(struct nameidata *nd, struct dentry *dentry
                         goto err_root;
         }
         spin_lock(&parent->d_lock);
-        spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
-        if (!__d_rcu_to_refcount(dentry, nd->seq))
-                goto err;
-        /*
-         * If the sequence check on the child dentry passed, then the child has
-         * not been removed from its parent. This means the parent dentry must
-         * be valid and able to take a reference at this point.
-         */
-        BUG_ON(!IS_ROOT(dentry) && dentry->d_parent != parent);
-        BUG_ON(!parent->d_count);
-        parent->d_count++;
-        spin_unlock(&dentry->d_lock);
+        if (!dentry) {
+                if (!__d_rcu_to_refcount(parent, nd->seq))
+                        goto err_parent;
+                BUG_ON(nd->inode != parent->d_inode);
+        } else {
+                spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
+                if (!__d_rcu_to_refcount(dentry, nd->seq))
+                        goto err_child;
+                /*
+                 * If the sequence check on the child dentry passed, then
+                 * the child has not been removed from its parent. This
+                 * means the parent dentry must be valid and able to take
+                 * a reference at this point.
+                 */
+                BUG_ON(!IS_ROOT(dentry) && dentry->d_parent != parent);
+                BUG_ON(!parent->d_count);
+                parent->d_count++;
+                spin_unlock(&dentry->d_lock);
+        }
         spin_unlock(&parent->d_lock);
         if (want_root) {
                 path_get(&nd->root);
@@ -501,8 +457,10 @@ static int nameidata_dentry_drop_rcu(struct nameidata *nd, struct dentry *dentry
         br_read_unlock(vfsmount_lock);
         nd->flags &= ~LOOKUP_RCU;
         return 0;
-err:
+
+err_child:
         spin_unlock(&dentry->d_lock);
+err_parent:
         spin_unlock(&parent->d_lock);
 err_root:
         if (want_root)
@@ -510,22 +468,6 @@ err_root:
         return -ECHILD;
 }
 
-/* Try to drop out of rcu-walk mode if we were in it, otherwise do nothing.  */
-static inline int nameidata_dentry_drop_rcu_maybe(struct nameidata *nd, struct dentry *dentry)
-{
-        if (nd->flags & LOOKUP_RCU) {
-                if (unlikely(nameidata_dentry_drop_rcu(nd, dentry))) {
-                        nd->flags &= ~LOOKUP_RCU;
-                        if (!(nd->flags & LOOKUP_ROOT))
-                                nd->root.mnt = NULL;
-                        rcu_read_unlock();
-                        br_read_unlock(vfsmount_lock);
-                        return -ECHILD;
-                }
-        }
-        return 0;
-}
-
 /**
  * nameidata_drop_rcu_last - drop nameidata ending path walk out of rcu-walk
  * @nd: nameidata pathwalk data to drop
@@ -1241,13 +1183,8 @@ static int do_lookup(struct nameidata *nd, struct qstr *name,
                 if (likely(__follow_mount_rcu(nd, path, inode, false)))
                         return 0;
 unlazy:
-                if (dentry) {
-                        if (nameidata_dentry_drop_rcu(nd, dentry))
-                                return -ECHILD;
-                } else {
-                        if (nameidata_drop_rcu(nd))
-                                return -ECHILD;
-                }
+                if (unlazy_walk(nd, dentry))
+                        return -ECHILD;
         } else {
                 dentry = __d_lookup(parent, name);
         }
@@ -1303,7 +1240,7 @@ static inline int may_lookup(struct nameidata *nd)
                 int err = exec_permission(nd->inode, IPERM_FLAG_RCU);
                 if (err != -ECHILD)
                         return err;
-                if (nameidata_drop_rcu(nd))
+                if (unlazy_walk(nd, NULL))
                         return -ECHILD;
         }
         return exec_permission(nd->inode, 0);
@@ -1357,8 +1294,12 @@ static inline int walk_component(struct nameidata *nd, struct path *path,
                 return -ENOENT;
         }
         if (unlikely(inode->i_op->follow_link) && follow) {
-                if (nameidata_dentry_drop_rcu_maybe(nd, path->dentry))
-                        return -ECHILD;
+                if (nd->flags & LOOKUP_RCU) {
+                        if (unlikely(unlazy_walk(nd, path->dentry))) {
+                                terminate_walk(nd);
+                                return -ECHILD;
+                        }
+                }
                 BUG_ON(inode != path->dentry->d_inode);
                 return 1;
         }