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Code Issues Releases Wiki Activity

nbd: reduce the nbd_index_mutex scope

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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: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20210811124428.2368491-7-hch@lst.de
[axboe: fix whitespace]
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Christoph Hellwig 2021-08-11 14:44:28 +02:00 committed by Jens Axboe
parent 6177b56c96
commit 6e4df4c648
1 changed files with 29 additions and 28 deletions
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57
drivers/block/nbd.c
View file

@ -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;
@ -1849,35 +1851,36 @@ 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)) {
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 until the nbd device is completely destroyed */
wait_for_completion(&destroy_complete);
goto again;
}
if (!refcount_inc_not_zero(&nbd->refs)) {
mutex_unlock(&nbd_index_mutex);
if (index == -1)
goto again;
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);
}
}
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_for_completion(&destroy_complete);
goto again;
}
if (!refcount_inc_not_zero(&nbd->refs)) {
mutex_unlock(&nbd_index_mutex);
if (index == -1)
goto again;
printk(KERN_ERR "nbd: device at index %d is going down\n",
index);
return -EINVAL;
}
mutex_unlock(&nbd_index_mutex);
mutex_lock(&nbd->config_lock);
if (refcount_read(&nbd->config_refs)) {
mutex_unlock(&nbd->config_lock);
@ -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;
}