Re: [PATCH v2 1/5] vfio: ccw: fix cleanup if cp_prefetch fails

Cornelia Huck
2018-04-23T11:40:54Z

On Mon, 23 Apr 2018 13:01:09 +0200
Dong Jia Shi <bjsdjshi@linux.vnet.ibm.com> wrote:

> From: Halil Pasic <pasic@linux.vnet.ibm.com>
>
> If the translation of a channel program fails, we may end up attempting
> to clean up (free, unpin) stuff that never got translated (and allocated,
> pinned) in the first place.
>
> By adjusting the lengths of the chains accordingly (so the element that
> failed, and all subsequent elements are excluded) cleanup activities
> based on false assumptions can be avoided.
>
> Let's make sure cp_free works properly after cp_prefetch returns with an
> error by setting ch_len of a ccw chain to the number of the translated
> CCWs on that chain.

Should that be cc:stable? This problem has been there probably since we
introduced vfio-ccw, no?

>
> Acked-by: Pierre Morel <pmorel@linux.vnet.ibm.com>
> Reviewed-by: Dong Jia Shi <bjsdjshi@linux.vnet.ibm.com>
> Signed-off-by: Halil Pasic <pasic@linux.vnet.ibm.com>
> Signed-off-by: Dong Jia Shi <bjsdjshi@linux.vnet.ibm.com>
> ---
> drivers/s390/cio/vfio_ccw_cp.c | 13 ++++++++++++-
> 1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/s390/cio/vfio_ccw_cp.c b/drivers/s390/cio/vfio_ccw_cp.c
> index 2c7550797ec2..62d66e195304 100644
> --- a/drivers/s390/cio/vfio_ccw_cp.c
> +++ b/drivers/s390/cio/vfio_ccw_cp.c
> @@ -715,6 +715,10 @@ void cp_free(struct channel_program *cp)
> * and stores the result to ccwchain list. @cp must have been
> * initialized by a previous call with cp_init(). Otherwise, undefined
> * behavior occurs.
> + * For each chain composing the channel program:
> + * - On entry ch_len holds the count of CCW to be translated.
> + * - On exit ch_len is adjusted to the count of successfully translated CCW.
> + * This allows cp_free to find in ch_len the count of CCW to free in a chain.

s/CCW/CCWs/ (x3)?

Can change on applying.

> *
> * The S/390 CCW Translation APIS (prefixed by 'cp_') are introduced
> * as helpers to do ccw chain translation inside the kernel. Basically
> @@ -749,11 +753,18 @@ int cp_prefetch(struct channel_program *cp)
> for (idx = 0; idx < len; idx++) {
> ret = ccwchain_fetch_one(chain, idx, cp);
> if (ret)
> - return ret;
> + goto out_err;
> }
> }
>
> return 0;
> +out_err:
> + /* Only cleanup the chain elements that were actually translated. */
> + chain->ch_len = idx;
> + list_for_each_entry_continue(chain, &cp->ccwchain_list, next) {
> + chain->ch_len = 0;
> + }
> + return ret;
> }
>
> /**

Else, looks good.