struct dentry *__d_lookup_rcu(const struct dentry *parent,
				const struct qstr *name,
				unsigned *seqp)
{
	u64 hashlen = name->hash_len;
	const unsigned char *str = name->name;
	struct hlist_bl_head *b = d_hash(hashlen_hash(hashlen));
	struct hlist_bl_node *node;
	struct dentry *dentry;

	/*
	 * Note: There is significant duplication with __d_lookup_rcu which is
	 * required to prevent single threaded performance regressions
	 * especially on architectures where smp_rmb (in seqcounts) are costly.
	 * Keep the two functions in sync.
	 */

	/*
	 * The hash list is protected using RCU.
	 *
	 * Carefully use d_seq when comparing a candidate dentry, to avoid
	 * races with d_move().
	 *
	 * It is possible that concurrent renames can mess up our list
	 * walk here and result in missing our dentry, resulting in the
	 * false-negative result. d_lookup() protects against concurrent
	 * renames using rename_lock seqlock.
	 *
	 * See Documentation/filesystems/path-lookup.txt for more details.
	 */
	hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {
		unsigned seq;

seqretry:
		/*
		 * The dentry sequence count protects us from concurrent
		 * renames, and thus protects parent and name fields.
		 *
		 * The caller must perform a seqcount check in order
		 * to do anything useful with the returned dentry.
		 *
		 * NOTE! We do a "raw" seqcount_begin here. That means that
		 * we don't wait for the sequence count to stabilize if it
		 * is in the middle of a sequence change. If we do the slow
		 * dentry compare, we will do seqretries until it is stable,
		 * and if we end up with a successful lookup, we actually
		 * want to exit RCU lookup anyway.
		 *
		 * Note that raw_seqcount_begin still *does* smp_rmb(), so
		 * we are still guaranteed NUL-termination of ->d_name.name.
		 */
		seq = raw_seqcount_begin(&dentry->d_seq);
		if (dentry->d_parent != parent)
			continue;
		if (d_unhashed(dentry))
			continue;

		if (unlikely(parent->d_flags & DCACHE_OP_COMPARE)) {
			int tlen;
			const char *tname;
			if (dentry->d_name.hash != hashlen_hash(hashlen))
				continue;
			tlen = dentry->d_name.len;
			tname = dentry->d_name.name;
			/* we want a consistent (name,len) pair */
			if (read_seqcount_retry(&dentry->d_seq, seq)) {
				cpu_relax();
				goto seqretry;
			}
			if (parent->d_op->d_compare(dentry,
						    tlen, tname, name) != 0)
				continue;
		} else {
			if (dentry->d_name.hash_len != hashlen)
				continue;
			if (dentry_cmp(dentry, str, hashlen_len(hashlen)) != 0)
				continue;
		}
		*seqp = seq;
		return dentry;
	}
	return NULL;
}

The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.