nbd: reset NBD to NULL when restarting in nbd_genl_connect

When nbd_genl_connect restarts to wait for a disconnecting device, nbd
needs to be reset to NULL.  Do that by facoring out a helper to find
an unused device.

Fixes: 6177b56c96ff ("nbd: refactor device search and allocation in nbd_genl_connect")
Reported-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Reported-by: Hillf Danton <hdanton@sina.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20210825163108.50713-3-hch@lst.de
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 0c1389d..938ca7f 100644 (file)
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -1781,6 +1781,20 @@ out:
        return ERR_PTR(err);
 }
 
+static struct nbd_device *nbd_find_unused(void)
+{
+       struct nbd_device *nbd;
+       int id;
+
+       lockdep_assert_held(&nbd_index_mutex);
+
+       idr_for_each_entry(&nbd_index_idr, nbd, id)
+               if (!refcount_read(&nbd->config_refs))
+                       return nbd;
+
+       return NULL;
+}
+
 /* Netlink interface. */
 static const struct nla_policy nbd_attr_policy[NBD_ATTR_MAX + 1] = {
        [NBD_ATTR_INDEX]                =       { .type = NLA_U32 },
@@ -1828,7 +1842,7 @@ static int nbd_genl_size_set(struct genl_info *info, struct nbd_device *nbd)
 static int nbd_genl_connect(struct sk_buff *skb, struct genl_info *info)
 {
        DECLARE_COMPLETION_ONSTACK(destroy_complete);
-       struct nbd_device *nbd = NULL;
+       struct nbd_device *nbd;
        struct nbd_config *config;
        int index = -1;
        int ret;
@@ -1849,20 +1863,10 @@ static int nbd_genl_connect(struct sk_buff *skb, struct genl_info *info)
        }
 again:
        mutex_lock(&nbd_index_mutex);
-       if (index == -1) {
-               struct nbd_device *tmp;
-               int id;
-
-               idr_for_each_entry(&nbd_index_idr, tmp, id) {
-                       if (!refcount_read(&tmp->config_refs)) {
-                               nbd = tmp;
-                               break;
-                       }
-               }
-       } else {
+       if (index == -1)
+               nbd = nbd_find_unused();
+       else
                nbd = idr_find(&nbd_index_idr, index);
-       }
-
        if (nbd) {
                if (test_bit(NBD_DESTROY_ON_DISCONNECT, &nbd->flags) &&
                    test_bit(NBD_DISCONNECT_REQUESTED, &nbd->flags)) {