Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754004Ab2KMMsI (ORCPT ); Tue, 13 Nov 2012 07:48:08 -0500 Received: from mx1.redhat.com ([209.132.183.28]:6621 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753250Ab2KMMsG (ORCPT ); Tue, 13 Nov 2012 07:48:06 -0500 Date: Tue, 13 Nov 2012 10:47:48 -0200 From: Rafael Aquini To: Andrew Morton Cc: Wei Yongjun , rusty@rustcorp.com.au, mst@redhat.com, yongjun_wei@trendmicro.com.cn, virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH -next] virtio: balloon: fix missing unlock on error in fill_balloon() Message-ID: <20121113124748.GA1636@optiplex.redhat.com> References: <20121112153453.fa3edc3d.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20121112153453.fa3edc3d.akpm@linux-foundation.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2770 Lines: 79 On Mon, Nov 12, 2012 at 03:34:53PM -0800, Andrew Morton wrote: > On Mon, 12 Nov 2012 21:50:40 +0800 > Wei Yongjun wrote: > > > From: Wei Yongjun > > > > 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 > > --- > > 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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/