Re: [PATCH] xen/blkback: prevent repeated backend_changedinvocations

From: Jan Beulich
Date: Thu Dec 13 2012 - 10:02:07 EST


>>> On 11.12.12 at 21:50, Olaf Hering <olaf@xxxxxxxxx> wrote:
> backend_changed might be called multiple times, which will leak
> be->mode. Make sure it will be called only once. Remove some unneeded
> checks. Also the be->mode string was leaked, release the memory on
> device shutdown.

So I decided to make an attempt myself, retaining the current
behavior of allowing multiple calls, yet not having to sprinkle
around multiple kfree()-s for be->mode. Slightly re-structuring
the function made this pretty strait forward.

Jan

> Signed-off-by: Olaf Hering <olaf@xxxxxxxxx>
> ---
>
> incorporate all comments from Jan.
> fold the oneline change to xen_blkbk_remove into this change
> now its compile tested.
>
> drivers/block/xen-blkback/xenbus.c | 69 ++++++++++++++++++--------------------
> 1 file changed, 33 insertions(+), 36 deletions(-)
>
> diff --git a/drivers/block/xen-blkback/xenbus.c
> b/drivers/block/xen-blkback/xenbus.c
> index f58434c..5ca77c3 100644
> --- a/drivers/block/xen-blkback/xenbus.c
> +++ b/drivers/block/xen-blkback/xenbus.c
> @@ -28,6 +28,7 @@ struct backend_info {
> unsigned major;
> unsigned minor;
> char *mode;
> + unsigned alive;
> };
>
> static struct kmem_cache *xen_blkif_cachep;
> @@ -366,6 +367,7 @@ static int xen_blkbk_remove(struct xenbus_device *dev)
> be->blkif = NULL;
> }
>
> + kfree(be->mode);
> kfree(be);
> dev_set_drvdata(&dev->dev, NULL);
> return 0;
> @@ -501,10 +503,14 @@ static void backend_changed(struct xenbus_watch *watch,
> = container_of(watch, struct backend_info, backend_watch);
> struct xenbus_device *dev = be->dev;
> int cdrom = 0;
> - char *device_type;
> + char *device_type, *p;
> + long handle;
>
> DPRINTK("");
>
> + if (be->alive)
> + return;
> +
> err = xenbus_scanf(XBT_NIL, dev->nodename, "physical-device", "%x:%x",
> &major, &minor);
> if (XENBUS_EXIST_ERR(err)) {
> @@ -520,12 +526,7 @@ static void backend_changed(struct xenbus_watch *watch,
> return;
> }
>
> - if ((be->major || be->minor) &&
> - ((be->major != major) || (be->minor != minor))) {
> - pr_warn(DRV_PFX "changing physical device (from %x:%x to %x:%x) not
> supported.\n",
> - be->major, be->minor, major, minor);
> - return;
> - }
> + be->alive = 1;
>
> be->mode = xenbus_read(XBT_NIL, dev->nodename, "mode", NULL);
> if (IS_ERR(be->mode)) {
> @@ -541,39 +542,35 @@ static void backend_changed(struct xenbus_watch *watch,
> kfree(device_type);
> }
>
> - if (be->major == 0 && be->minor == 0) {
> - /* Front end dir is a number, which is used as the handle. */
> -
> - char *p = strrchr(dev->otherend, '/') + 1;
> - long handle;
> - err = strict_strtoul(p, 0, &handle);
> - if (err)
> - return;
> -
> - be->major = major;
> - be->minor = minor;
> + /* Front end dir is a number, which is used as the handle. */
> + p = strrchr(dev->otherend, '/') + 1;
> + err = strict_strtoul(p, 0, &handle);
> + if (err)
> + return;
>
> - err = xen_vbd_create(be->blkif, handle, major, minor,
> - (NULL == strchr(be->mode, 'w')), cdrom);
> - if (err) {
> - be->major = 0;
> - be->minor = 0;
> - xenbus_dev_fatal(dev, err, "creating vbd structure");
> - return;
> - }
> + be->major = major;
> + be->minor = minor;
>
> - err = xenvbd_sysfs_addif(dev);
> - if (err) {
> - xen_vbd_free(&be->blkif->vbd);
> - be->major = 0;
> - be->minor = 0;
> - xenbus_dev_fatal(dev, err, "creating sysfs entries");
> - return;
> - }
> + err = xen_vbd_create(be->blkif, handle, major, minor,
> + (NULL == strchr(be->mode, 'w')), cdrom);
> + if (err) {
> + be->major = 0;
> + be->minor = 0;
> + xenbus_dev_fatal(dev, err, "creating vbd structure");
> + return;
> + }
>
> - /* We're potentially connected now */
> - xen_update_blkif_status(be->blkif);
> + err = xenvbd_sysfs_addif(dev);
> + if (err) {
> + xen_vbd_free(&be->blkif->vbd);
> + be->major = 0;
> + be->minor = 0;
> + xenbus_dev_fatal(dev, err, "creating sysfs entries");
> + return;
> }
> +
> + /* We're potentially connected now */
> + xen_update_blkif_status(be->blkif);
> }
>
>
> --
> 1.8.0.1


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