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Commit 3825bdb7 authored by Christoph Hellwig's avatar Christoph Hellwig Committed by Al Viro
Browse files

fs: use RCU read side protection in d_validate 



d_validate does a purely read lookup in the dentry hash, so use RCU read side
locking instead of dcache_lock.  Split out from a larget patch by
Nick Piggin <npiggin@suse.de>.

Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent a4633357

fs/dcache.c

+12 −19
Original line number Diff line number Diff line
@@ -1491,33 +1491,26 @@ struct dentry *d_hash_and_lookup(struct dentry *dir, struct qstr *name) 
 * This is used by ncpfs in its readdir implementation.

 * Zero is returned in the dentry is invalid.

 */

 

int d_validate(struct dentry *dentry, struct dentry *dparent)

int d_validate(struct dentry *dentry, struct dentry *parent)

{

	struct hlist_head *base;

	struct hlist_node *lhp;

	struct hlist_head *head = d_hash(parent, dentry->d_name.hash);

	struct hlist_node *node;

	struct dentry *d;



	/* Check whether the ptr might be valid at all.. */

	if (!kmem_ptr_validate(dentry_cache, dentry))

		goto out;



	if (dentry->d_parent != dparent)

		goto out;

		return 0;

	if (dentry->d_parent != parent)

		return 0;



	spin_lock(&dcache_lock);

	base = d_hash(dparent, dentry->d_name.hash);

	hlist_for_each(lhp,base) { 

		/* hlist_for_each_entry_rcu() not required for d_hash list

		 * as it is parsed under dcache_lock

		 */

		if (dentry == hlist_entry(lhp, struct dentry, d_hash)) {

			__dget_locked(dentry);

			spin_unlock(&dcache_lock);

	rcu_read_lock();

	hlist_for_each_entry_rcu(d, node, head, d_hash) {

		if (d == dentry) {

			dget(dentry);

			return 1;

		}

	}

	spin_unlock(&dcache_lock);

out:

	rcu_read_unlock();

	return 0;

}

EXPORT_SYMBOL(d_validate);