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[204.195.22.127]) by smtp.gmail.com with ESMTPSA id c88-v6sm30723525pfe.132.2018.08.14.09.35.17 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 14 Aug 2018 09:35:17 -0700 (PDT) Date: Tue, 14 Aug 2018 09:35:14 -0700 From: Stephen Hemminger To: "Michael Kelley (EOSG)" Cc: KY Srinivasan , "gregkh@linuxfoundation.org" , "linux-kernel@vger.kernel.org" , "devel@linuxdriverproject.org" , "olaf@aepfle.de" , "apw@canonical.com" , "jasowang@redhat.com" , Stephen Hemminger , "vkuznets@redhat.com" Subject: Re: [PATCH 2/5] vmbus: add driver_override support Message-ID: <20180814093514.7febc8d5@xeon-e3> In-Reply-To: References: <20180810230520.2055-1-kys@linuxonhyperv.com> <20180810230611.2114-1-kys@linuxonhyperv.com> <20180810230611.2114-2-kys@linuxonhyperv.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 13 Aug 2018 19:30:50 +0000 "Michael Kelley (EOSG)" wrote: > > +/* > > + * Return a matching hv_vmbus_device_id pointer. > > + * If there is no match, return NULL. > > + */ > > +static const struct hv_vmbus_device_id *hv_vmbus_get_id(struct hv_driver *drv, > > + struct hv_device *dev) > > +{ > > + const uuid_le *guid = &dev->dev_type; > > + const struct hv_vmbus_device_id *id; > > > > - return NULL; > > + /* When driver_override is set, only bind to the matching driver */ > > + if (dev->driver_override && strcmp(dev->driver_override, drv->name)) > > + return NULL; > > This function needs to be covered by the device lock, so that > dev->driver_override can't be set to NULL and the memory freed > during the above 'if' statement. When called from vmbus_probe(), > the device lock is held, so it's good. But when called from > vmbus_match(), the device lock may not be held: consider the path > __driver_attach() -> driver_match_device() -> vmbus_match(). The function hv_vmbus_get_id is called from that path. i.e. __device_attach -> driver-match_device -> vmbus_match. and __device_attach always does: device_lock(dev); The code in driver _override_store uses the same device_lock when storing the new value. This is same locking as is done in pci-sysfs.c