diff options
| -rw-r--r-- | fs/namei.c | 151 |
1 files changed, 46 insertions, 105 deletions
diff --git a/fs/namei.c b/fs/namei.c index 54fc993e302..1039cbae0c1 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; } |