On Mon, Feb 24, 2025 at 09:20:40PM +0000, Al Viro wrote: > Do that before new dentry is visible anywhere. It does create > a new possible state for dentries present in ->d_children/->d_sib - > DCACHE_PAR_LOOKUP present, negative, unhashed, not in in-lookup > hash chains, refcount positive. Those are going to be skipped > by all tree-walkers (both d_walk() callbacks in fs/dcache.c and > explicit loops over children/sibling lists elsewhere) and > dput() is fine with those. > > NOTE: dropping the final reference to a "normal" in-lookup dentry > (in in-lookup hash) is a bug - somebody must've forgotten to > call d_lookup_done() on it and bad things will happen. With those > it's OK; if/when we get around to making __dentry_kill() complain > about such breakage, remember that predicate to check should > *not* be just d_in_lookup(victim) but rather a combination of that > with hlist_bl_unhashed(&victim->d_u.d_in_lookup_hash). Might > be worth to consider later... > > Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx> > --- Reviewed-by: Christian Brauner <brauner@xxxxxxxxxx> > fs/dcache.c | 10 +++++++--- > 1 file changed, 7 insertions(+), 3 deletions(-) > > diff --git a/fs/dcache.c b/fs/dcache.c > index 29db27228d97..9ad7cbb5a6b0 100644 > --- a/fs/dcache.c > +++ b/fs/dcache.c > @@ -2518,13 +2518,19 @@ struct dentry *d_alloc_parallel(struct dentry *parent, > unsigned int hash = name->hash; > struct hlist_bl_head *b = in_lookup_hash(parent, hash); > struct hlist_bl_node *node; > - struct dentry *new = d_alloc(parent, name); > + struct dentry *new = __d_alloc(parent->d_sb, name); > struct dentry *dentry; > unsigned seq, r_seq, d_seq; > > if (unlikely(!new)) > return ERR_PTR(-ENOMEM); This is minor but it would be clearer if the __d_alloc() call was placed directly above the error handling. > > + new->d_flags |= DCACHE_PAR_LOOKUP; > + spin_lock(&parent->d_lock); > + new->d_parent = dget_dlock(parent); > + hlist_add_head(&new->d_sib, &parent->d_children); > + spin_unlock(&parent->d_lock); > + > retry: > rcu_read_lock(); > seq = smp_load_acquire(&parent->d_inode->i_dir_seq); > @@ -2608,8 +2614,6 @@ struct dentry *d_alloc_parallel(struct dentry *parent, > return dentry; > } > rcu_read_unlock(); > - /* we can't take ->d_lock here; it's OK, though. */ > - new->d_flags |= DCACHE_PAR_LOOKUP; > new->d_wait = wq; > hlist_bl_add_head(&new->d_u.d_in_lookup_hash, b); > hlist_bl_unlock(b); > -- > 2.39.5 >
