Commit 6e4df4c6 authored by Christoph Hellwig's avatar Christoph Hellwig Committed by Jens Axboe
Browse files

nbd: reduce the nbd_index_mutex scope 



nbd_index_mutex is currently held over add_disk and inside ->open, which
leads to lock order reversals.  Refactor the device creation code path
so that nbd_dev_add is called without nbd_index_mutex lock held and
only takes it for the IDR insertation.

Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20210811124428.2368491-7-hch@lst.de


[axboe: fix whitespace]
Reviewed-by: default avatarJosef Bacik <josef@toxicpanda.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 6177b56c

drivers/block/nbd.c

+28 −27
Original line number Diff line number Diff line
@@ -1683,7 +1683,7 @@ static const struct blk_mq_ops nbd_mq_ops = { 
	.timeout	= nbd_xmit_timeout,

};



static struct nbd_device *nbd_dev_add(int index)

static struct nbd_device *nbd_dev_add(int index, unsigned int refs)

{

	struct nbd_device *nbd;

	struct gendisk *disk;
@@ -1709,6 +1709,7 @@ static struct nbd_device *nbd_dev_add(int index) 
	if (err)

		goto out_free_nbd;



	mutex_lock(&nbd_index_mutex);

	if (index >= 0) {

		err = idr_alloc(&nbd_index_idr, nbd, index, index + 1,

				GFP_KERNEL);
@@ -1719,6 +1720,7 @@ static struct nbd_device *nbd_dev_add(int index) 
		if (err >= 0)

			index = err;

	}

	mutex_unlock(&nbd_index_mutex);

	if (err < 0)

		goto out_free_tags;

	nbd->index = index;
@@ -1745,7 +1747,7 @@ static struct nbd_device *nbd_dev_add(int index) 


	mutex_init(&nbd->config_lock);

	refcount_set(&nbd->config_refs, 0);

	refcount_set(&nbd->refs, 1);

	refcount_set(&nbd->refs, refs);

	INIT_LIST_HEAD(&nbd->list);

	disk->major = NBD_MAJOR;

	disk->first_minor = index << part_shift;
@@ -1849,21 +1851,13 @@ static int nbd_genl_connect(struct sk_buff *skb, struct genl_info *info) 
		nbd = idr_find(&nbd_index_idr, index);

	}



	if (!nbd) {

		nbd = nbd_dev_add(index);

		if (IS_ERR(nbd)) {

			mutex_unlock(&nbd_index_mutex);

			pr_err("nbd: failed to add new device\n");

			return PTR_ERR(nbd);

		}

	}



	if (nbd) {

		if (test_bit(NBD_DESTROY_ON_DISCONNECT, &nbd->flags) &&

		    test_bit(NBD_DISCONNECT_REQUESTED, &nbd->flags)) {

			nbd->destroy_complete = &destroy_complete;

			mutex_unlock(&nbd_index_mutex);



		/* Wait untill the the nbd stuff is totally destroyed */

			/* wait until the nbd device is completely destroyed */

			wait_for_completion(&destroy_complete);

			goto again;

		}
@@ -1872,11 +1866,20 @@ static int nbd_genl_connect(struct sk_buff *skb, struct genl_info *info) 
			mutex_unlock(&nbd_index_mutex);

			if (index == -1)

				goto again;

		printk(KERN_ERR "nbd: device at index %d is going down\n",

			pr_err("nbd: device at index %d is going down\n",

				index);

			return -EINVAL;

		}

		mutex_unlock(&nbd_index_mutex);

	} else {

		mutex_unlock(&nbd_index_mutex);



		nbd = nbd_dev_add(index, 2);

		if (IS_ERR(nbd)) {

			pr_err("nbd: failed to add new device\n");

			return PTR_ERR(nbd);

		}

	}



	mutex_lock(&nbd->config_lock);

	if (refcount_read(&nbd->config_refs)) {
@@ -2432,10 +2435,8 @@ static int __init nbd_init(void) 
	}

	nbd_dbg_init();



	mutex_lock(&nbd_index_mutex);

	for (i = 0; i < nbds_max; i++)

		nbd_dev_add(i);

	mutex_unlock(&nbd_index_mutex);

		nbd_dev_add(i, 1);

	return 0;

}