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Commit a734eb45 authored by Nick Piggin's avatar Nick Piggin
Browse files

fs: dcache reduce d_parent locking 



Use RCU to simplify locking in dget_parent.

Signed-off-by: default avatarNick Piggin <npiggin@kernel.dk>
parent dc0474be

fs/dcache.c

+12 −9
Original line number Diff line number Diff line
@@ -446,24 +446,27 @@ struct dentry *dget_parent(struct dentry *dentry) 
	struct dentry *ret;



repeat:

	spin_lock(&dentry->d_lock);

	/*

	 * Don't need rcu_dereference because we re-check it was correct under

	 * the lock.

	 */

	rcu_read_lock();

	ret = dentry->d_parent;

	if (!ret)

		goto out;

	if (dentry == ret) {

		ret->d_count++;

	if (!ret) {

		rcu_read_unlock();

		goto out;

	}

	if (!spin_trylock(&ret->d_lock)) {

		spin_unlock(&dentry->d_lock);

		cpu_relax();

	spin_lock(&ret->d_lock);

	if (unlikely(ret != dentry->d_parent)) {

		spin_unlock(&ret->d_lock);

		rcu_read_unlock();

		goto repeat;

	}

	rcu_read_unlock();

	BUG_ON(!ret->d_count);

	ret->d_count++;

	spin_unlock(&ret->d_lock);

out:

	spin_unlock(&dentry->d_lock);

	return ret;

}

EXPORT_SYMBOL(dget_parent);