On Tue, Sep 10, 2013 at 11:25:44AM -0700, Linus Torvalds wrote: > nd->flags &= ~LOOKUP_RCU; > if (!(nd->flags & LOOKUP_ROOT)) > nd->root.mnt = NULL; > unlock_rcu_walk(); > > and my unlazy_walk() essentially terminated the walk _without_ > clearing that nd->root.mnt thing (it did clear the LOOKUP_RCU bit and > unlock_rcy_walk(). So then later, we'd end up doing an extra > path_put(). Explaining a zero d_lockref.count. > > The whole damn root.mnt behavior with !LOOKUP_ROOT is a mystery and > needs more comments. But the attached trivial patch should do the > missing portion of terminate_walk(). > > Al, can you walk us through the rules for what "root.mnt == NULL" > really means? It's basically used as a flag for whether we've gotten > the root pointer or not. But it's pretty damn esoteric.
LOOKUP_ROOT: the caller has set nd->root and we shouldn't touch that at all. !LOOKUP_ROOT: we set nd->root the first time we need / (in the very beginning if it's an absolute pathname, on the first absolute symlink otherwise). In non-RCU mode we hold a reference to it; in RCU mode we do not. As the result, leaving RCU mode should either grab a reference to the damn thing (if we intend to go on) or zero it out. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
