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SubjectRe: [PATCH] xen/blkback: prevent repeated backend_changed invocations
On Thu, Dec 13, 2012 at 03:02:11PM +0000, Jan Beulich wrote:
> >>> On 11.12.12 at 21:50, Olaf Hering <olaf@aepfle.de> 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.

<nods> Would it be possible to post a patch?

>
> Jan
>
> > Signed-off-by: Olaf Hering <olaf@aepfle.de>
> > ---
> >
> > 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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