Re: [PATCH 2/4] virtio_blk: Less function calls in init_vq() after error detection

Christian Borntraeger
2016-09-13T12:54:58Z

On 09/13/2016 02:13 PM, SF Markus Elfring wrote:
> From: Markus Elfring <elfring@users.sourceforge.net>
> Date: Tue, 13 Sep 2016 13:20:44 +0200
>
> The kfree() function was called in up to three cases
> by the init_vq() function during error handling even if
> the passed variable contained a null pointer.
>
> * Split a condition check for memory allocation failures.
>
> * Adjust jump targets according to the Linux coding style convention.
>
> Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
> ---
> drivers/block/virtio_blk.c | 22 +++++++++++++++++-----
> 1 file changed, 17 insertions(+), 5 deletions(-)

Can't you see from this diffstat that the patch actually seems to makes
the code more complex?
In addition, please have a look at commit 347a529398e8e723338cca5d8a8ae2d9e7e93448
virtio_blk: Fix a slient kernel panic

which did the opposite of your patch. And in fact it fixed a bug. Quite obviously
multiple labels are harder to read and harder to get right. For error handling with
just kfree one label is just the right thing to.

>
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 6553eb7..d28dbcf 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -395,11 +395,21 @@ static int init_vq(struct virtio_blk *vblk)
> return -ENOMEM;
>
> names = kmalloc_array(num_vqs, sizeof(*names), GFP_KERNEL);
> + if (!names) {
> + err = -ENOMEM;
> + goto free_vblk_vqs;
> + }
> +
> callbacks = kmalloc_array(num_vqs, sizeof(*callbacks), GFP_KERNEL);
> + if (!callbacks) {
> + err = -ENOMEM;
> + goto free_names;
> + }
> +
> vqs = kmalloc_array(num_vqs, sizeof(*vqs), GFP_KERNEL);
> - if (!names || !callbacks || !vqs) {
> + if (!vqs) {
> err = -ENOMEM;
> - goto out;
> + goto free_callbacks;
> }
>
> for (i = 0; i < num_vqs; i++) {
> @@ -411,19 +421,21 @@ static int init_vq(struct virtio_blk *vblk)
> /* Discover virtqueues and write information to configuration. */
> err = vdev->config->find_vqs(vdev, num_vqs, vqs, callbacks, names);
> if (err)
> - goto out;
> + goto free_vqs;
>
> for (i = 0; i < num_vqs; i++) {
> spin_lock_init(&vblk->vqs[i].lock);
> vblk->vqs[i].vq = vqs[i];
> }
> vblk->num_vqs = num_vqs;
> -
> -out:
> + free_vqs:
> kfree(vqs);
> + free_callbacks:
> kfree(callbacks);
> + free_names:
> kfree(names);
> if (err)
> + free_vblk_vqs:
> kfree(vblk->vqs);
> return err;
> }
>