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d_alloc_parallel(): set DCACHE_PAR_LOOKUP earlier

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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 considering later...

Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2025-02-24 10:36:46 -05:00
parent 691fb82ca6
commit e95db51c81
1 changed files with 7 additions and 3 deletions
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10
fs/dcache.c
View file

@ -2546,13 +2546,19 @@ 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);
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);
@ -2636,8 +2642,6 @@ retry:
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);