Re: [PATCH v6 17/25] rnbd: client: main functionality

Bart Van Assche
2020-01-02T23:55:13Z

On 12/30/19 2:29 AM, Jack Wang wrote:
> +MODULE_DESCRIPTION("InfiniBand Network Block Device Client");

InfiniBand or RDMA?

> +static int rnbd_clt_set_dev_attr(struct rnbd_clt_dev *dev,
> + const struct rnbd_msg_open_rsp *rsp)
> +{
> + struct rnbd_clt_session *sess = dev->sess;
> +
> + if (unlikely(!rsp->logical_block_size))
> + return -EINVAL;
> +
> + dev->device_id = le32_to_cpu(rsp->device_id);
> + dev->nsectors = le64_to_cpu(rsp->nsectors);
> + dev->logical_block_size = le16_to_cpu(rsp->logical_block_size);
> + dev->physical_block_size = le16_to_cpu(rsp->physical_block_size);
> + dev->max_write_same_sectors = le32_to_cpu(rsp->max_write_same_sectors);
> + dev->max_discard_sectors = le32_to_cpu(rsp->max_discard_sectors);
> + dev->discard_granularity = le32_to_cpu(rsp->discard_granularity);
> + dev->discard_alignment = le32_to_cpu(rsp->discard_alignment);
> + dev->secure_discard = le16_to_cpu(rsp->secure_discard);
> + dev->rotational = rsp->rotational;
> +
> + dev->max_hw_sectors = sess->max_io_size / dev->logical_block_size;

The above statement looks suspicious to me. The unit of the second
argument of blk_queue_max_hw_sectors() is 512 bytes. Since
dev->max_hw_sectors is passed as the second argument to
blk_queue_max_hw_sectors() I think it should also have 512 bytes as unit
instead of the logical block size.

> +static int rnbd_clt_change_capacity(struct rnbd_clt_dev *dev,
> + size_t new_nsectors)
> +{
> + int err = 0;
> +
> + rnbd_clt_info(dev, "Device size changed from %zu to %zu sectors\n",
> + dev->nsectors, new_nsectors);
> + dev->nsectors = new_nsectors;
> + set_capacity(dev->gd,
> + dev->nsectors * (dev->logical_block_size /
> + SECTOR_SIZE));
> + err = revalidate_disk(dev->gd);
> + if (err)
> + rnbd_clt_err(dev,
> + "Failed to change device size from %zu to %zu, err: %d\n",
> + dev->nsectors, new_nsectors, err);
> + return err;
> +}

Please document the unit of nsectors in struct rnbd_clt_dev. Please also
document the unit of the 'new_nsectors' argument.

The set_capacity() call can only be correct if the unit of dev->nsectors
is one logical block. Is that really the case?

> +static void msg_io_conf(void *priv, int errno)
> +{
> + struct rnbd_iu *iu = priv;
> + struct rnbd_clt_dev *dev = iu->dev;
> + struct request *rq = iu->rq;
> +
> + iu->status = errno ? BLK_STS_IOERR : BLK_STS_OK;
> +
> + blk_mq_complete_request(rq);
> +
> + if (errno)
> + rnbd_clt_info_rl(dev, "%s I/O failed with err: %d\n",
> + rq_data_dir(rq) == READ ? "read" : "write",
> + errno);
> +}

Accessing 'rq' after having called blk_mq_complete_request() may trigger
a use-after-free. Please don't do that.

> +static void wait_for_rtrs_disconnection(struct rnbd_clt_session *sess)
> +__releases(&sess_lock)
> +__acquires(&sess_lock)

Please indent __releases() and __acquires() annotations.

> +{
> + DEFINE_WAIT_FUNC(wait, autoremove_wake_function);
> +
> + prepare_to_wait(&sess->rtrs_waitq, &wait, TASK_UNINTERRUPTIBLE);
> + if (IS_ERR_OR_NULL(sess->rtrs)) {
> + finish_wait(&sess->rtrs_waitq, &wait);
> + return;
> + }
> + mutex_unlock(&sess_lock);
> + /* After unlock session can be freed, so careful */
> + schedule();
> + mutex_lock(&sess_lock);
> +}

How can a function that calls schedule() and that is not surrounded by a
loop be correct? What if e.g. schedule() finishes due to a spurious wakeup?

> +static struct rnbd_clt_session *__find_and_get_sess(const char *sessname)
> +__releases(&sess_lock)
> +__acquires(&sess_lock)
> +{
> + struct rnbd_clt_session *sess;
> + int err;
> +
> +again:
> + list_for_each_entry(sess, &sess_list, list) {
> + if (strcmp(sessname, sess->sessname))
> + continue;
> +
> + if (unlikely(sess->rtrs_ready && IS_ERR_OR_NULL(sess->rtrs)))
> + /*
> + * No RTRS connection, session is dying.
> + */
> + continue;
> +
> + if (likely(rnbd_clt_get_sess(sess))) {
> + /*
> + * Alive session is found, wait for RTRS connection.
> + */
> + mutex_unlock(&sess_lock);
> + err = wait_for_rtrs_connection(sess);
> + if (unlikely(err))
> + rnbd_clt_put_sess(sess);
> + mutex_lock(&sess_lock);
> +
> + if (unlikely(err))
> + /* Session is dying, repeat the loop */
> + goto again;
> +
> + return sess;
> + }
> + /*
> + * Ref is 0, session is dying, wait for RTRS disconnect
> + * in order to avoid session names clashes.
> + */
> + wait_for_rtrs_disconnection(sess);
> + /*
> + * RTRS is disconnected and soon session will be freed,
> + * so repeat a loop.
> + */
> + goto again;
> + }
> +
> + return NULL;
> +}

Since wait_for_rtrs_disconnection() unlocks sess_lock, can the
list_for_each_entry() above trigger a use-after-free of sess->next?

> +static size_t rnbd_clt_get_sg_size(struct scatterlist *sglist, u32 len)
> +{
> + struct scatterlist *sg;
> + size_t tsize = 0;
> + int i;
> +
> + for_each_sg(sglist, sg, len, i)
> + tsize += sg->length;
> + return tsize;
> +}

Please follow the example of other block drivers and use blk_rq_bytes()
instead of iterating over the sg-list.

> +static int setup_mq_tags(struct rnbd_clt_session *sess)
> +{
> + struct blk_mq_tag_set *tags = &sess->tag_set;
> +
> + memset(tags, 0, sizeof(*tags));
> + tags->ops = &rnbd_mq_ops;
> + tags->queue_depth = sess->queue_depth;
> + tags->numa_node = NUMA_NO_NODE;
> + tags->flags = BLK_MQ_F_SHOULD_MERGE |
> + BLK_MQ_F_TAG_SHARED;
> + tags->cmd_size = sizeof(struct rnbd_iu);
> + tags->nr_hw_queues = num_online_cpus();
> +
> + return blk_mq_alloc_tag_set(tags);
> +}

Please change the name of the "tags" pointer into "tag_set".

> +static int index_to_minor(int index)
> +{
> + return index << RNBD_PART_BITS;
> +}
> +
> +static int minor_to_index(int minor)
> +{
> + return minor >> RNBD_PART_BITS;
> +}

Is it useful to introduce functions that encapsulate a single shift
operation?

> + blk_queue_virt_boundary(dev->queue, 4095);

The virt_boundary parameter must match the RDMA memory registration page
size. Please introduce a symbolic constant for the RDMA memory
registration page size such that these two parameters stay in sync in
case anyone would want to change the memory registration page size.

> +static void rnbd_clt_setup_gen_disk(struct rnbd_clt_dev *dev, int idx)
> +{
> + dev->gd->major = rnbd_client_major;
> + dev->gd->first_minor = index_to_minor(idx);
> + dev->gd->fops = &rnbd_client_ops;
> + dev->gd->queue = dev->queue;
> + dev->gd->private_data = dev;
> + snprintf(dev->gd->disk_name, sizeof(dev->gd->disk_name), "rnbd%d",
> + idx);
> + pr_debug("disk_name=%s, capacity=%zu\n",
> + dev->gd->disk_name,
> + dev->nsectors * (dev->logical_block_size / SECTOR_SIZE)
> + );
> +
> + set_capacity(dev->gd, dev->nsectors * (dev->logical_block_size /
> + SECTOR_SIZE));

Again, what is the unit of dev->nsectors?

> +static void rnbd_clt_add_gen_disk(struct rnbd_clt_dev *dev)
> +{
> + add_disk(dev->gd);
> +}

Is it useful to introduce this wrapper around add_disk()?

Thanks,

Bart.