52b993b4c4
commit 78b1a52e05c9db11d293342e8d6d8a230a04b4e7 upstream. While ccw_io_helper() seems like intended to be exclusive in a sense that it is supposed to facilitate I/O for at most one thread at any given time, there is actually nothing ensuring that threads won't pile up at vcdev->wait_q. If they do, all threads get woken up and see the status that belongs to some other request than their own. This can lead to bugs. For an example see: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1788432 This race normally does not cause any problems. The operations provided by struct virtio_config_ops are usually invoked in a well defined sequence, normally don't fail, and are normally used quite infrequent too. Yet, if some of the these operations are directly triggered via sysfs attributes, like in the case described by the referenced bug, userspace is given an opportunity to force races by increasing the frequency of the given operations. Let us fix the problem by ensuring, that for each device, we finish processing the previous request before starting with a new one. Signed-off-by: Halil Pasic <pasic@linux.ibm.com> Reported-by: Colin Ian King <colin.king@canonical.com> Cc: stable@vger.kernel.org Message-Id: <20180925121309.58524-3-pasic@linux.ibm.com> Signed-off-by: Cornelia Huck <cohuck@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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.