iommufd: Break the loop on failure in iommufd_fault_fops_read()

commit 172fc8b upstream.

On a copy_to_user() failure inside the inner list_for_each_entry, only the
inner loop breaks; the outer while re-fetches the just-restored fault group
and retries the failing copy_to_user() forever, spinning the reader at 100%
CPU with fault->mutex held.

Check rc after the inner loop and break the outer while as well.

Fixes: 07838f7 ("iommufd: Add iommufd fault object")
Link: https://patch.msgid.link/r/336a9b6e44fe66a24199d3be777c405c85c98622.1780343944.git.nicolinc@nvidia.com
Cc: stable@vger.kernel.org
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
Reviewed-by: Pranjal Shrivastava <praan@google.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: nicolinc

drivers/iommu/iommufd/eventq.c

@@ -168,6 +168,8 @@ static ssize_t iommufd_fault_fops_read(struct file *filep, char __user *buf,
 			}
 			done += fault_size;
 		}
+		if (rc)
+			break;
 	}
 	mutex_unlock(&fault->mutex);