Re: [Xen-devel] [PATCH] xen/blkback: prevent repeated backend_changed invocations

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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



_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel