On Mon, Nov 12, 2012 at 03:34:53PM -0800, Andrew Morton wrote: > On Mon, 12 Nov 2012 21:50:40 +0800 > Wei Yongjun <weiyj.lk@xxxxxxxxx> wrote: > > > From: Wei Yongjun <yongjun_wei@xxxxxxxxxxxxxxxxx> > > > > Add the missing unlock before return from function fill_balloon() > > in the error handling case. > > > > Introduced by 9864a8(virtio_balloon: introduce migration primitives > > to balloon pages) > > > > dpatch engine is used to auto generate this patch. > > (https://github.com/weiyj/dpatch) > > > > Signed-off-by: Wei Yongjun <yongjun_wei@xxxxxxxxxxxxxxxxx> > > --- > > drivers/virtio/virtio_balloon.c | 4 +++- > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c > > index f70151b..72e8dcb 100644 > > --- a/drivers/virtio/virtio_balloon.c > > +++ b/drivers/virtio/virtio_balloon.c > > @@ -152,8 +152,10 @@ static void fill_balloon(struct virtio_balloon *vb, size_t num) > > } > > > > /* Didn't get any? Oh well. */ > > - if (vb->num_pfns == 0) > > + if (vb->num_pfns == 0) { > > + mutex_unlock(&vb->balloon_lock); > > return; > > + } > > > > tell_host(vb, vb->inflate_vq); > > mutex_unlock(&vb->balloon_lock); > > Well. Why did this bug occur in the first place? Because > fill_balloon() has multiple return points and one of those was > overlooked when adding new locking. > > This (and the addition of memory leaks) is quite common. It is part of > the reason why so much kernel code uses goto's to avoid multiple return > points. A maintainability thing. > > And we can fix this shortcoming in fill_balloon() without even needing a > goto: > > --- a/drivers/virtio/virtio_balloon.c~virtio_balloon-introduce-migration-primitives-to-balloon-pages-fix-fix > +++ a/drivers/virtio/virtio_balloon.c > @@ -151,13 +151,9 @@ static void fill_balloon(struct virtio_b > totalram_pages--; > } > > - /* Didn't get any? Oh well. */ > - if (vb->num_pfns == 0) { > - mutex_unlock(&vb->balloon_lock); > - return; > - } > - > - tell_host(vb, vb->inflate_vq); > + /* Did we get any? */ > + if (vb->num_pfns != 0) > + tell_host(vb, vb->inflate_vq); > mutex_unlock(&vb->balloon_lock); > } > Your fix is far better, as it simplifies the code without loosing that test -- which only evaluates as true, if we fail to allocate a page right after getting into the loop -- /me thinks driver folks place it there to not bother tell_host() and the virt_queues if no pageframe is present at that pfns array. _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
