From mboxrd@z Thu Jan 1 00:00:00 1970 From: Juan Quintela Subject: Re: [PATCH 3/3] vhost: fix get_user_pages_fast error handling Date: Tue, 23 Feb 2010 20:56:56 +0100 Message-ID: References: <82ba8c97ce55dd4bf9972ad755961cd14e6a0938.1266943453.git.mst@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Rusty Russell , kvm@vger.kernel.org, virtualization@lists.osdl.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, David Miller , markmc@redhat.com, gleb@redhat.com, herbert.xu@redhat.com, dlaor@redhat.com, avi@redhat.com To: "Michael S. Tsirkin" Return-path: In-Reply-To: <82ba8c97ce55dd4bf9972ad755961cd14e6a0938.1266943453.git.mst@redhat.com> (Michael S. Tsirkin's message of "Tue, 23 Feb 2010 18:57:58 +0200") Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org "Michael S. Tsirkin" wrote: > get_user_pages_fast returns number of pages on success, negative value > on failure, but never 0. Fix vhost code to match this logic. It can return 0 if you ask for 0 pages :) >>From the comment: * Returns number of pages pinned. This may be fewer than the number * requested. If nr_pages is 0 or negative, returns 0. If no pages * were pinned, returns -errno. */ I agree that code was wrong, but the BUG_ON() is not neccessary IMHO. The important bit is the change in the comparison. Reviewed-by: Juan Quintela > Signed-off-by: Michael S. Tsirkin > --- > drivers/vhost/vhost.c | 3 ++- > 1 files changed, 2 insertions(+), 1 deletions(-) > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > index d4f8fdf..d003504 100644 > --- a/drivers/vhost/vhost.c > +++ b/drivers/vhost/vhost.c > @@ -646,8 +646,9 @@ static int set_bit_to_user(int nr, void __user *addr) > int bit = nr + (log % PAGE_SIZE) * 8; > int r; > r = get_user_pages_fast(log, 1, 1, &page); > - if (r) > + if (r < 0) > return r; > + BUG_ON(r != 1); > base = kmap_atomic(page, KM_USER0); > set_bit(bit, base); > kunmap_atomic(base, KM_USER0);