Re: Q: spin_unlock(dentry) after lock_parent(dentry)

["J. R. Okajima" <hooanon05g@gmail.com>]

Al Viro:
> Nope.  You are misreading it.  Note that in *all* cases the parent is
> locked.  And NULL is returned exactly in the case when that parent is
	:::

Thanks.
Please allow me another question.

In the case of concurrent dentry_kill() and shrink_dentry_list(),
dentry_kill() kills the dentry and calls list_del(&dentry->d_u.d_child).
lock_parent() (called by shrink_dentry_list()) doesn't check d_child
nor DCACHE_DENTRY_KILLED. So shrink_dentry_list() may get a parent of a
dead dentry and tries traversing via d_parent.
Is it correct to track d_parent after list_del(&dentry->d_u.d_child)?
Should lock_parent() consider DCACHE_DENTRY_KILLED too?

--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -533,7 +533,8 @@ failed:
 static inline struct dentry *lock_parent(struct dentry *dentry)
 {
 	struct dentry *parent = dentry->d_parent;
-	if (IS_ROOT(dentry))
+	if (IS_ROOT(dentry)
+	    || (dentry->d_flags & DCACHE_DENTRY_KILLED))
 		return NULL;
 	if (likely(spin_trylock(&parent->d_lock)))
 		return parent;


J. R. Okajima