IB/uverbs: Avoid a crash on device hot remove

Wait until all users have closed their device context before allowing
device unregistration to complete.  This prevents a crash caused by
referring to stale data structures.

A better solution would be to have a way to revoke contexts rather
than waiting for userspace to close the context, but that's a much
bigger change that will have to wait.  For now let's at least avoid
the crash.

Signed-off-by: Jack Morgenstein <jackm@mellanox.co.il>
Signed-off-by: Michael S. Tsirkin <mst@mellanox.co.il>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

1 files changed, 7 insertions, 1 deletions

diff --git a/drivers/infiniband/core/uverbs_main.c b/drivers/infiniband/core/uverbs_main.c
index e725cccc7cde..4e16314e8e6d 100644
--- a/drivers/infiniband/core/uverbs_main.c
+++ b/drivers/infiniband/core/uverbs_main.c
@@ -122,7 +122,7 @@ static void ib_uverbs_release_dev(struct kref *ref)
         struct ib_uverbs_device *dev =
                 container_of(ref, struct ib_uverbs_device, ref);
 
-        kfree(dev);
+        complete(&dev->comp);
 }
 
 void ib_uverbs_release_ucq(struct ib_uverbs_file *file,
@@ -740,6 +740,7 @@ static void ib_uverbs_add_one(struct ib_device *device)
                 return;
 
         kref_init(&uverbs_dev->ref);
+        init_completion(&uverbs_dev->comp);
 
         spin_lock(&map_lock);
         uverbs_dev->devnum = find_first_zero_bit(dev_map, IB_UVERBS_MAX_DEVICES);
@@ -793,6 +794,8 @@ err_cdev:
 
 err:
         kref_put(&uverbs_dev->ref, ib_uverbs_release_dev);
+        wait_for_completion(&uverbs_dev->comp);
+        kfree(uverbs_dev);
         return;
 }
 
@@ -812,7 +815,10 @@ static void ib_uverbs_remove_one(struct ib_device *device)
         spin_unlock(&map_lock);
 
         clear_bit(uverbs_dev->devnum, dev_map);
+
         kref_put(&uverbs_dev->ref, ib_uverbs_release_dev);
+        wait_for_completion(&uverbs_dev->comp);
+        kfree(uverbs_dev);
 }
 
 static int uverbs_event_get_sb(struct file_system_type *fs_type, int flags,