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When a netfront device is set up it registers a netdev fairly early on, before it has set up the queues and is actually usable. A userspace tool like NetworkManager will immediately try to open it and access its state as soon as it appears. The bug can be reproduced by hotplugging VIFs until the VM runs out of grant refs. It registers the netdev but fails to set up any queues (since there are no more grant refs). In the meantime, NetworkManager opens the device and the kernel crashes trying to access the queues (of which there are none). Fix this in two ways: * For initial setup, register the netdev much later, after the queues are setup. This avoids the race entirely. * During a suspend/resume cycle, the frontend reconnects to the backend and the queues are recreated. It is possible (though highly unlikely) to race with something opening the device and accessing the queues after they have been destroyed but before they have been recreated. Extend the region covered by the rtnl semaphore to protect against this race. There is a possibility that we fail to recreate the queues so check for this in the open function. Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com> Signed-off-by: Juergen Gross <jgross@suse.com>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.