RDMA/device: Fix a race between mad_client and cm_client init

The mad_client will be initialized in enable_device_and_get(), while the
devices_rwsem will be downgraded to a read semaphore. There is a window
that leads to the failed initialization for cm_client, since it can not
get matched mad port from ib_mad_port_list, and the matched mad port will
be added to the list after that.

    mad_client    |                       cm_client
------------------|--------------------------------------------------------
ib_register_device|
enable_device_and_get
down_write(&devices_rwsem)
xa_set_mark(&devices, DEVICE_REGISTERED)
downgrade_write(&devices_rwsem)
                  |
                  |ib_cm_init
                  |ib_register_client(&cm_client)
                  |down_read(&devices_rwsem)
                  |xa_for_each_marked (&devices, DEVICE_REGISTERED)
                  |add_client_context
                  |cm_add_one
                  |ib_register_mad_agent
                  |ib_get_mad_port
                  |__ib_get_mad_port
                  |list_for_each_entry(entry, &ib_mad_port_list, port_list)
                  |return NULL
                  |up_read(&devices_rwsem)
                  |
add_client_context|
ib_mad_init_device|
ib_mad_port_open  |
list_add_tail(&port_priv->port_list, &ib_mad_port_list)
up_read(&devices_rwsem)
                  |

Fix it by using down_write(&devices_rwsem) in ib_register_client().

Fixes: d0899892edd0 ("RDMA/device: Provide APIs from the core code to help unregistration")
Link: https://lore.kernel.org/r/20240203035313.98991-1-lishifeng@sangfor.com.cn
Suggested-by: Jason Gunthorpe <jgg@ziepe.ca>
Signed-off-by: Shifeng Li <lishifeng@sangfor.com.cn>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

diff --git a/drivers/infiniband/core/device.c b/drivers/infiniband/core/device.c
index 67bcea7..07cb6c5 100644 (file)
--- a/drivers/infiniband/core/device.c
+++ b/drivers/infiniband/core/device.c
@@ -1730,7 +1730,7 @@ static int assign_client_id(struct ib_client *client)
 {
        int ret;
 
-       down_write(&clients_rwsem);
+       lockdep_assert_held(&clients_rwsem);
        /*
         * The add/remove callbacks must be called in FIFO/LIFO order. To
         * achieve this we assign client_ids so they are sorted in
@@ -1739,14 +1739,11 @@ static int assign_client_id(struct ib_client *client)
        client->client_id = highest_client_id;
        ret = xa_insert(&clients, client->client_id, client, GFP_KERNEL);
        if (ret)
-               goto out;
+               return ret;
 
        highest_client_id++;
        xa_set_mark(&clients, client->client_id, CLIENT_REGISTERED);
-
-out:
-       up_write(&clients_rwsem);
-       return ret;
+       return 0;
 }
 
 static void remove_client_id(struct ib_client *client)
@@ -1776,25 +1773,35 @@ int ib_register_client(struct ib_client *client)
 {
        struct ib_device *device;
        unsigned long index;
+       bool need_unreg = false;
        int ret;
 
        refcount_set(&client->uses, 1);
        init_completion(&client->uses_zero);
+
+       /*
+        * The devices_rwsem is held in write mode to ensure that a racing
+        * ib_register_device() sees a consisent view of clients and devices.
+        */
+       down_write(&devices_rwsem);
+       down_write(&clients_rwsem);
        ret = assign_client_id(client);
        if (ret)
-               return ret;
+               goto out;
 
-       down_read(&devices_rwsem);
+       need_unreg = true;
        xa_for_each_marked (&devices, index, device, DEVICE_REGISTERED) {
                ret = add_client_context(device, client);
-               if (ret) {
-                       up_read(&devices_rwsem);
-                       ib_unregister_client(client);
-                       return ret;
-               }
+               if (ret)
+                       goto out;
        }
-       up_read(&devices_rwsem);
-       return 0;
+       ret = 0;
+out:
+       up_write(&clients_rwsem);
+       up_write(&devices_rwsem);
+       if (need_unreg && ret)
+               ib_unregister_client(client);
+       return ret;
 }
 EXPORT_SYMBOL(ib_register_client);