From mboxrd@z Thu Jan 1 00:00:00 1970 From: Cornelia Huck Subject: Re: [PATCH v2] virtio_blk: Fix a slient kernel panic Date: Mon, 18 Jul 2016 18:25:34 +0200 Message-ID: <20160718182534.7b0bdfe9.cornelia.huck@de.ibm.com> References: <1468850489-40157-1-git-send-email-mnghuan@gmail.com> <20160718172128.5b8c10b1.cornelia.huck@de.ibm.com> <20160718160421.GA20047@huangminfeis-MacBook-Pro.local> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20160718160421.GA20047@huangminfeis-MacBook-Pro.local> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Minfei Huang Cc: Minfei Huang , virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, fanc.fnst@cn.fujitsu.com, mst@redhat.com List-Id: virtualization@lists.linuxfoundation.org On Tue, 19 Jul 2016 00:18:32 +0800 Minfei Huang wrote: > On 07/18/16 at 05:21P, Cornelia Huck wrote: > > On Mon, 18 Jul 2016 22:01:29 +0800 > > Minfei Huang wrote: > > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c > > > index 42758b5..d920512 100644 > > > --- a/drivers/block/virtio_blk.c > > > +++ b/drivers/block/virtio_blk.c > > > @@ -381,9 +381,9 @@ static int init_vq(struct virtio_blk *vblk) > > > { > > > int err = 0; > > > int i; > > > - vq_callback_t **callbacks; > > > - const char **names; > > > - struct virtqueue **vqs; > > > + vq_callback_t **callbacks = NULL; > > > + const char **names = NULL; > > > + struct virtqueue **vqs = NULL; > > > > If you init the variables to NULL anyway... > > Hi, Cornelia. > > Thanks for reviewing this patch. > > Seems there is no need to init these variables to NULL. I will remove > them laster. Fine with me. > > > > > > unsigned short num_vqs; > > > struct virtio_device *vdev = vblk->vdev; > > > > > > @@ -394,22 +394,16 @@ static int init_vq(struct virtio_blk *vblk) > > > num_vqs = 1; > > > > > > > ...just do > > > > err = -ENOMEM; > > > > here and... > > > > > vblk->vqs = kmalloc(sizeof(*vblk->vqs) * num_vqs, GFP_KERNEL); > > > - if (!vblk->vqs) { > > > - err = -ENOMEM; > > > - goto out; > > > - } > > > + if (!vblk->vqs) > > > + return -ENOMEM; > > > > > > names = kmalloc(sizeof(*names) * num_vqs, GFP_KERNEL); > > > - if (!names) > > > - goto err_names; > > > - > > > callbacks = kmalloc(sizeof(*callbacks) * num_vqs, GFP_KERNEL); > > > - if (!callbacks) > > > - goto err_callbacks; > > > - > > > vqs = kmalloc(sizeof(*vqs) * num_vqs, GFP_KERNEL); > > > - if (!vqs) > > > - goto err_vqs; > > > + if (!names || !callbacks || !vqs) { > > > + err = -ENOMEM; > > > + goto out; > > > + } > > > > ...you could use the > > > > foo = kmalloc(...); > > if (!foo) > > goto out; > > > > sequence in any case. This avoids trying again and again if e.g. the > > names allocation already failed. > > For this implementation, I have referred others which calls > vdev->config->find_vqs as well. Yes, this continues trying to allocate > memory, although memory allocation failed before. It might not be the best idea, though; although it should hopefully be a not-so-common occurrence. > > > > > Alternatively, you should be fine if you don't init the variables to > > NULL: The code is now either taking an early exit or setting all of the > > variables anyway. > > > > It's a big change if we refactor the helper ->find_vqs, since other > devices also call it. Actually, I was referring to not initializing the variables to NULL in this function and keeping the rest of your changes: IOW, just what you suggested above :)